Dwayne P. Weary
Manager, Mission Analysis and Systems Engineering Office
Lunar and Mars Exploration Program Office
David I. Kaplan
Architecture Analysis Lead
Lunar and Mars Exploration Program Office
Many persons performed analyses and wrote segments of this document. The key points-of-contact on the NASA team in various disciplines included:
Any comments or questions regarding this document may be addressed to:
--David Kaplan
2.0 ARCHITECTURE REFERENCE DESCRIPTION
4.0 ISSUES/ALTERNATIVES/STUDIES
APPENDIX A: MISSION TRAJECTORY DATA
APPENDIX B: STRAWMAN SCIENCE PAYLOAD DATA
The Lunar and Mars Exploration Program Office (LMEPO) at the Johnson Space Center has led the architecture analysis effort and was responsible for coordinating and integrating the inputs received from the participating NASA Centers. The four Architecture White Papers contain a first-order assessment of the technical and strategic details required to implement the four Synthesis Group architectures. The purpose of the analysis effort has been to develop a thorough understanding of the implications of pursuing the architecture objectives outlined by the Synthesis Group and to provide complete descriptions of implementations that are consistent with those objectives. The analysis effort was intentionally constrained to examine the unaltered objectives and strategies presented in the Synthesis Group architectures. Thus, the Architecture White Papers present only a possible implementation of one of the Synthesis Group architectures. There has been no attempt to determine or present an optimal implementation, nor does the implementation presented in each White Paper represent a recommended approach on the part of NASA.
The Synthesis Group architecture descriptions contained a number of specific and detailed mission- and system-level recommendations in addition to the higher-level architecture goals and strategies. These recommendations were followed, whenever possible, in conducting the analysis of the architectures in order to be as consistent as possible with the intent of the Synthesis Group. The Architecture Analysis Ground Rules and Assumptions document (AAGRA ) Version 2.1, published by LMEPO, contains the study assumptions for each architecture and serves as technical guidance for analysis of the Synthesis Group architectures.
There will be four White Papers at the conclusion of the architecture analysis effort; one for each of the four recommended Synthesis Group architectures. This White Paper presents the results of the analysis for only the Mars Exploration Architecture. However, all the White Papers employ the same format and table of contents. Section 2 of each White Paper outlines the architecture objectives, the key milestones and accomplishments, the technology/advanced development and human support strategies, and the end-to-end mission description. Section 3 provides detailed descriptions of the various systems defined for the architecture implementation, the reasoning behind the selections of the systems employed, and an overview of how the particular system is operated during the various phases of development within an architecture. Section 4 of each White Paper lists possible issues with the Synthesis Group recommendations for the architecture, provides alternative strategies/implementations, and outlines additional analysis that may be needed before any recommendations can be made for a particular area.
In addition to the four White Papers, at the conclusion of the architecture analysis effort, a summary of the results and recommendations across all four architectures will be documented in a volume entitled "Architecture Analysis Summary and Recommendations." The purpose of this document is not to merely compile the various results and recommendations from the analysis of each architecture, but to determine how the results and recommendations for each architecture complement or contradict each other. These results will be used to define features that are common to all architectural goals as well as those features that are specific to particular architectural goals. In addition, these results will provide the foundation from which an Initial Operational Capability (IOC) can be determined for the Space Exploration Initiative (SEI).
The first and second missions to the Moon, occurring in 2005 and 2006, substantiate a human presence on an extraterrestrial surface. Precursor missions are not deemed necessary to successfully place a crew on the Moon; rather, Apollo-era data is used to negotiate an outpost location. Recall that the presence on the Moon is intended as risk abatement toward a Mars mission as opposed to exploring new lunar territory. The third lunar mission in 2007 extends the crew's surface duration, thus expanding the database on humans in a harsh, partial-gravity environment. The fourth and fifth lunar missions, both flown in 2009, provide the core opportunity for testing martian systems and operations. These two missions comprise the dress rehearsal, the key focus of lunar activities for the Mars Exploration architecture.
During the lunar preparatory phase of this architecture, precursor missions are flown to Mars to gather the data necessary for selecting Mars landing sites. A minimum set of robotic infrastructure is included, in keeping with the minimalist approach. Five years after the dress rehearsal, the first human mission to explore Mars is launched in 2014. The successful completion of this initial mission leads to a second Mars exploration mission in 2016 to a different and unique location.
General strategy for the Mars Exploration architecture is summarized by the following points:
The function of the Moon as a testing stage for human missions to Mars precludes the easy growth of surface facilities and thus human expansion. In addition, the austere accommodations provide just enough living space to accomplish given activities. The lunar outpost and rehearsal sites are subsequently abandoned once Mars systems and operations are evaluated; therefore, activities to help sustain a lunar settlement (such as adding habitation facilities and advancing life support systems) are not aligned with this strategy. Note that the crew size remains the same at six during the lunar missions. In this architecture, crew size is dependent on mission activities as opposed to expanding human presence. Furthermore, surface stay times begin at fourteen days and extend to 90 days with no intent for longer missions or consistently rotating crews.
The Mars portion of the Mars Exploration architecture focuses on the initial exploration of the planet by humans. The second piloted mission for a period of 600 days tests the human capability of staying on another planet for more than a year. At that point in the architecture, the total surface time on both the Moon and Mars (~300 days) does not approach the new 600-day limit. The architecture alludes to the human presence intent if follow-on missions are approved. The exploration phase allows for evaluation of the potential for long-term habitation by proving extended stay capabilities and the feasibility of in-situ resource utilization.
Lunar and martian science performed under these limitations primarily emphasizes the disciplines of geology and traverse geophysics, with some observations in astronomy and space physics. The major science accomplishments are in the areas of geologic reconnaissance and geophysics. The instrumentation for associated studies is limited in complexity, low in mass, and relatively easy to transport. Human EVAs provide geophysical traverses across varied terrains, enable human excursions in the field, and provide samples for Earth laboratories to investigate. Robotic rovers complement the human effort with simultaneous rudimentary traverse science and sample collection. Astronomy and space physics, while providing unprecedented data-sets to Earth, are nevertheless limited by the minimal accommodation of small automated instrument packages near the outposts. These disciplines of astronomy and space physics suffer due to their larger mass and operational requirements not supportable within the boundaries of this architecture. Similarly, experimental life sciences for human, plant and lower animal research take a low priority because time, crew availability and capability provided by the mission does not enable these type of studies.
The following discussion accounts the science strategy and accomplishments of each operational capability within the Mars Exploration architecture.
Lunar IOC The first fourteen-day mission contains no substantial science. Crew activities focus on preparing the outpost site and deploying the habitation facilities. Collection of large regolith samples is possible with the intent of Earth testing for potential resource utilization. The second fourteen-day mission allows minimal geologic exploration within a two kilometer radius about the selected outpost site, with the crew performing local exploration and deploying small instruments. The science emphasis is on reconnaisance geology and traverse geophysics. Scientific payloads require minimal crew support and outpost accommodations. The accomplishments of this phase are dominated by outpost emplacement activities.
Lunar NOC-1 The initial activity during this phase requires the crew to test and evaluate the pressurized rover on the Moon. The use of the pressurized rover extends the science capabilities from the outpost. The crew increases their time spent exploring (and testing rover systems) and decreases their time spent at the outpost. The pressurized excursions allow the crew to explore beyond two kilometers from the outpost, extending the range of deployment of small geophysical and astronomical instruments. A balance is established between traverse science, field work, and sample collection with instrument deployment. Although some sample examination is practiced on the Moon, the majority of the analyses is conducted on Earth.
Lunar NOC-2 The orbital dress rehearsal scheduled during this phase provides the opportunity for the "orbital crew to accomplish meaningful science using telerobotic systems on the lunar surface." The 120 days in lunar orbit allows practice of telescience and imaging/remote sensing observations which continue once the crew arrives at the dress rehearsal site. Although the dress rehearsal crew is concerned with Mars simulation operations, field work at the new site is possible. The site selection and the strategic investigations conducted are relevant to those planned for Mars. The crew accomplishes geotraverses, instrument deployment, and life science experimentation similar to activities planned on the Mars excursion. Sample returns from the lunar rehearsal site occur during and after simulating Mars operations via the secondary support crew.
Mars IOC The Earth-Mars transit affords the opportunity to conduct cruise science, including solar observations, astrophysics, experimental biomedicine, and discretionary science. While in Mars orbit the crew accomplishes investigations similar to those practiced in lunar orbit, including remote sensing, visual obserations, and telerobotic exploration. The first human mission to the martian surface focuses on scientific exploration around the landing site given a pressurized rover, a small suite of instruments, and a period of approximately 100 days. A balance is established between local exploration and pressurized excursions. Only basic analyses are possible at the martian outpost; the achievement is twofold: first hand observational science, and the return of substantial samples back to Earth. This phase also allows teleoperations of robotic rovers from the outpost in order to extend access, exploration and discovery to beyond the landing site.
Mars NOC Cruise science, en route to Mars and on return to Earth, continues during the second human transit. Orbital investigations similar to those conducted in Mars IOC provide additional data for mapping the martian surface. The second human landing expands the scientific domain by selection of a different site and an extended duration. The access to the martian surface and diversity of martian environments also increases. Anticipated scientific accomplishments are similar to Mars IOC with the additional potential to understand more complex scientific questions.
The general strategy for the Mars Exploration architecture does not emphasize space resource development. The function of the Moon as a testing stage for human missions to Mars precludes the investigation of resource utilization. The lunar outpost and rehearsal sites are abandoned once Mars systems and operations are evaluated; therefore, activities to help sustain a lunar program (such as producing propellant stock for landers) are not aligned with this strategy. The only effective use of resources on the Moon is the burial of the habitation facility in order to protect the crew from cosmic and solar radiation.
The major focus of the Mars missions is to explore new territory with humans. The first mission, due to surface duration limitations, affords little opportunity for human performance beyond initial exploration and science. The second mission, given a surface duration of 600 days, allows time for experimentation in addition to exploration. According to the Synthesis Group report, "an in situ resource demonstration unit is included in this mission to test the feasibility of producing fuels at Mars." Such a demonstration provides information for advancing human existence and extending the exploration capability on future Mars visits.
A portable life support system is necessary for activities outside the spacecraft or on excursions away from the habitat on planetary surfaces. This system should be simple and lightweight while still providing continuous life support for extended excursions.
A typical cargo mission to the Moon is initiated by the launch of two 150 mt-class ETO launch vehicles to a low Earth staging orbit. A 160 n.m., circular Earth orbit was chosen as the optimal location for the vehicle staging point. The two ETO launch elements rendezvous and dock together to complete the lunar transportation system stack. Once the docking operation is complete the vehicle systems are verified prior to Earth departure. The Lunar Transportation System is propulsively captured into a low altitude lunar orbit. Once in lunar orbit, the LEV separates from the LTV and descends to a precision landing at the desired landing site.
All of the transportation elements are expended in this architecture, as shown in Table 2.3-1. The cargo LTV remains in lunar orbit for a subsequent controlled deorbit to the lunar surface. Note that the impact of this vehicle with the surface can serve as a seismic disturbance for a geophysical network. The cargo LEV is expended on the surface of the Moon.
A typical piloted mission to the Moon is shown in Figure 2.3-1; it is also initiated by the launch of two 150 mt-class ETO launch vehicles to LEO. The two ETO launch elements rendezvous and dock together to complete the lunar transportation system stack. Crew transportation to LEO can be accomplished via the Shuttle or on the ETO launch system if man-rated. Once the docking operation is complete the vehicle systems are verified prior to Earth departure. The Lunar Transportation System is propulsively captured into a low-altitude lunar orbit. Once in lunar orbit, the LEV separates from the LTV and descends for a precision landing near the previously deployed cargo. The piloted LTV remains in lunar orbit during the crew surface mission. After the nominal surface mission, the crew is transported in the LEV back to LLO to rendezvous with the LTV. The piloted LEV remains in lunar orbit for a subsequent controlled deorbit to the lunar surface. Prior to arrival at Earth, the crew enters an Earth direct-entry capsule for either a water or land recovery. The piloted LTV flies by Earth and is expended in Earth-Moon space.
Lunar mission milestones are presented in Figure 2.3-2. This figure provides a general summary for the remainder of the discussion in section 2.3.2.
Two cargo missions (four 150 mt launches) are required to deliver the initial outpost infrastructure in early 2005. The cargo landers perform precision autonomous landings at the desired landing site. Many of the operations associated with the initial outpost emplacement and set-up are conducted remotely from Earth to minimize the initial crew's involvement. All operations which can not be performed remotely are conducted by the crew upon arrival.
Crew departure from LEO is not initiated until the lunar outpost systems have been verified from Earth. The objective of the first crew is to demonstrate the safe return to the Moon, and to complete the emplacement of the outpost elements. Six crew depart from LEO in early 2005 with five descending to the lunar surface for 14 days. Initial crew operations are conducted via extravehicular activity (EVA) or intravehicular activity (IVA) from within the LEV. A minimum of 3 days habitation (two days nominal with one day of contingency) within the LEV is provided for outpost set-up and checkout. Science is limited to activities which support outpost emplacement, with additional science as time allows.
Another five-member crew returns to the first landing site in early 2006 for another 14 Earth days, living in the habitat (with the sixth crew member remaining in lunar orbit). The objective of this second crew is to verify the operation of the outpost after the first crew's departure and to perform local science near the outpost. Science activities include reconnaissance geology and exploration, sample collection for Earth return, and deployment of small instruments. If an Apollo site is chosen, equipment left behind from that mission is examined to determine the effect of long-term exposure on the lunar surface. Certain elements are disassembled and brought back to Earth for analysis. The successful completion of this flight constitutes achieving the Initial Operational Capability.
The operational strategy for the mission, science, and support infrastructure is shown in Table 2.3-2. In addition, this table presents the evolution of the operations strategy from an Earth-based system to a more distributed system as the operational capabilities progress.
The initial crew activities focus on upgrading the lunar infrastructure for the extended surface missions including emplacing a nuclear power source needed to supply additional power for lunar night activities. Once upgrades of the facilities are complete, activities focus on science and the planned Mars simulation. During local EVA's with the unpressurized rover and longer pressurized-rover excursions, the crew makes observations, conducts geoscience experiments, and emplaces additional monitoring instruments. Reconnaissance missions from the outpost are conducted to select a nearby Mars rehearsal landing site on the Moon. The NOC-1 crew also begins verification of some of the dress rehearsal operations. Equipment is configured to permit continued remote operations and obtain further reliability data subsequent to the crew's departure.
The lunar simulation follows the same sequence as the forthcoming Mars mission, comprising two distinct segments. The first segment consists of cargo missions which pre-deploy the initial habitat and power systems for the surface crew. This cargo lands on the surface and is verified remotely prior to crew departure about one year later. During the second segment the crew lands on the surface and lives out of the pre-deployed outpost.
Several differences must be noted between the lunar and martian missions. First, the Moon is essentially void of an atmosphere and therefore radiation shielding is required to protect the crew from galactic cosmic radiation and solar flares. This shielding can be accomplished by designing the required protection into the habitation elements or by covering the habitats with a layer of lunar regolith. The lunar regolith option is preferred due to mission mass savings. In contrast, Mars has an atmosphere, although rather tenuous, adequate to provide moderate protection for lower altitude landing sites. Therefore, unloading and covering the habitats on Mars may not be required as it is on the Moon.
Second, the energy requirements (measured in terms of velocity change required or DV) needed for descent and ascent from the surfaces of the Moon and Mars are significantly different. These differences are given in Table 2.3-3 and result from the different mass of the two planets and the presence of an atmosphere on Mars. As noted, the atmosphere of Mars is relatively thin, but can provide significant advantages for descent via drag deceleration.
Third, the environment of the Moon is unique from that of Mars. The lunar diurnal period is approximately 655 hours long, whereas the martian diurnal period is approximately 24 hours. This greatly accentuates the differences between the surface systems particularly in terms of power, thermal control, fluid conditioning, and thermal cycling.
Due to these variances between the lunar and martian environments, the actual simulations may be limited to subsystems and operations, rather than complete end-to-end hardware tests. Tests are conducted where possible.
This Mars simulation is initiated with the launch of three cargo missions to the lunar surface in early 2008 (Figure 2.3-3). These flights carry a Mars-type surface outpost, similar to the one to be used for the planned Mars mission. This surface cargo is pre-deployed remotely from Earth, similar to the initial outpost emplacement.
These three cargo missions are followed by another cargo mission in mid 2008, for the delivery of the Mars Transfer Vehicle (MTV) habitation system to lunar orbit. This orbital transfer mission is required to place the MTV systems into orbit prior to departure of the crew. The MTV systems provide living quarters for the dress rehearsal crew similar to those to be used in the eventual Mars mission.
The crew portion of the Mars simulation begins in early 2009 with six crew members spending 120 days in lunar orbit and 30 days on the surface, followed by an immediate return to Earth. This combination simulation of zero gravity and one-sixth gravity provides vital information regarding the issue of human health and performance after long exposure to zero and partial gravity, and the effectiveness of countermeasures to long term exposure to zero gravity. In addition, the degree of autonomy required in systems and equipment is better assessed after understanding crew adaptability to a reduced gravity environment. While in orbit, the crew engages in additional science experiments including remote observations of the Moon and Earth and gains experience in teleoperations of a lunar surface rover predeployed in the cargo flight.
Once on the surface crew members adapt in facilities on the Moon, performing tasks similar to those required at Mars. They conduct a 30-day science program that simulates EVA activities and instrument deployment and operational techniques that will be used on Mars. These crew members also experience the psychological effects and isolation that will be experienced by crews traveling to and from Mars. Operational concepts are developed to make best use of the systems and crew on the planetary surfaces, as outlined in Table 2.3-2.
While the Mars simulation flight is in progress, a second mission is flown by another six-member crew in mid 2009. This crew descends and lands at the original site with no delay in lunar orbit . This mission is planned to have them present on the lunar surface when the orbiting rehearsal crew lands. Three of the crew members drive to the Mars rehearsal site in a rover and finalize emplacement of the outpost . These activities include covering the habitation elements with regolith for radiation protection, an operation not required at Mars. In addition, the support crew provides assistance if necessary to the Mars rehearsal crew after they land. This crew will assist in performing necessary life science experiments and protocols. They stay on the Moon after the rehearsal crew departs, verifying equipment operations up to a total mission duration of approximately 90 days. Additional science and exploration is also accomplished during this time, with pressurized and unpressurized expeditions.
The successful completion of this phase of lunar operations constitutes the Mars mission dress rehearsal. When successfully completed, the Mars mission can proceed with minimum risk. If redesigns are required that necessitate further testing on the Moon, there are opportunities to fly additional missions in 2010 and 2011 prior to launching the Mars cargo mission in 2012.
Analyses have shown that the higher degree of splitting, i.e., the more mass the cargo vehicle transports, the better the overall initial mass in LEO (IMLEO), but correspondingly the higher the level of risk and mission complexity. As can be seen in Figure 2.3-4, the difference in the total mission mass in LEO between the various split modes is about 10% (~200 tons). At this level of analysis, this mass differential is insignificant relative to the uncertainty in the numbers themselves. Therefore, the baseline decision for the Mars Exploration architecture is the All-up mode. (A final decision should be made only after further studies and assessments are performed.)
The mission by mission timeline for the Mars mission phase of the Mars Exploration architecture is shown in Figure 2.3-5. Heliocentric trajectory plots and mission ÆV budgets for each flight are provided in Appendix A.
Figure 2.3-5 Mars Exploration Architecture Mission Set
The outbound trajectories of these two mission types can be roughly matched for four of seven trans-Mars departure windows in the 15-year synodic cycle. This suggests several mission strategies for these opportunities. First, the same Mars transfer vehicle can be designed to accomplish either of the mission classes from a propulsive standpoint, with the excess performance available for the Long-Duration-Stay option utilized by reducing the transit times. This could allow the same vehicle design to perform a Short-Duration-Stay mission for the initial Mars expedition, followed by a series of longer surface stays. Second, if the fast-transit mission, with its associated long Mars stay-time represents the nominal mission, the return leg of the short-duration-stay mission can act as an "early return" abort if the landing must be abandoned after insertion into Mars orbit. (The alternative would be to wait ~600 days in Mars orbit until the fast-transit window opens.)
The nuclear propulsion choice appears to allow the flexibility in mission design that is required to accommodate an integrated mission approach coupled with a realistic abort strategy. For example, the total ÆV for these missions is on the order of 14 km/sec, a regime in which a nuclear thermal propulsion (NTP) vehicle begins to look very attractive. When one considers including an option for a realistic abort strategy, which is discussed next, the NTP vehicle appears to be enabling, assuming realistic values for initial mass in LEO.
In general, it is thought that for the challenging Mars mission, free-return aborts are not sufficient to provide for safe crew-return in the event of a propulsion system failure. A flawless injection onto the free-return trajectory is required. In addition, the abort capability is lost when the terminal Mars orbit targeting takes place. Therefore, this abort mode offers protection only during the ballistic trans-Mars coast. It is also difficult to justify an abort scenario in which protecting against mechanical failures necessitates placing the crew in a high-risk environment (i.e., longer exposure to radiation and zero-g). Finally, a low-probability event like an abort substantially drives vehicle designs with no gain in mission productivity, thus increasing the cost and complexity of the nominal mission. Because of these limitations, the recommended approach is to require redundant Mars transfer vehicle main propulsion capability (probably in the form of multiple engines, tanks, and propellant lines) along with a powered abort strategy which allows a faster return of the crew using the degraded propulsion capability.
The Mars excursion vehicle (MEV) is sized to allow the descent stage to function in either a piloted and cargo mode. Due to the uncertainties in the long-duration storage of cryogenic propellants, storable propellants are selected for use on both the ascent and descent stages of the MEV.
Power: Nuclear surface power (SP-100 class) is used from the start of surface activities. A backup photovoltaic power system is provided.
Surface Mobility: Extravehicular mobility units (EMUs) are provided for each crew member. The same suit is used for both the Moon and Mars, however, the portable life support systems are different. Unpressurized rovers are brought to the martian surfaces with the crews on the piloted landers. Pressurized rovers are also used in this architecture. To expand the exploration capability, a power cart and experiment/sample trailer are used with the pressurized rover. All rovers are powered by fuel cells. Finally, teleoperated vehicles are used for unloading, construction, and mining purposes.
Two site reconnaissance orbiters are launched to Mars in December, 1998. The Synthesis Group Report has stated that the capability of a communications orbiter is to be combined with each reconnaissance orbiter, if feasible. The feasibility of this combination is discussed in Section 3.1 with the detailed implementation of the spacecraft. A minimum energy trajectory profile was selected for these flights launching in December 1998; arrival at Mars occurs 287 days after launch. Upon arrival at Mars the reconnaissance spacecraft are placed into 300 km altitude, sun-synchronous orbits to begin the mapping phase of their mission. The nominal duration for this phase is 20 months. Due to spacecraft lifetime issues, (the first piloted flight arrives at Mars 16 years later) and communications rate limitations, separate, more capable communications orbiters are required to support the piloted phase of the Mars exploration. The implementation of these orbiters is also presented in Section 3.1.
Allowing sufficient time to reduce the data from this mapping phase overlaps with the next launch opportunity (2001). Therefore, the site characterization rovers are launched to Mars the following two opportunities (2003 and 2005). The spacecraft fly minimum energy trajectories, launching in June, 2003 and August, 2005, respectively. Upon arrival at Mars, the spacecraft are placed into a low altitude orbit, from which the rovers are de-orbited. The nominal lifetime for each rover mission on the surface is two years.
A summary of the operations strategy for the Mars precursor missions, as well as for Mars IOC and NOC, is presented in Table 2.3-4.
Three cargo landers are needed to deliver the required mass to the martian surface. A fully integrated cargo lander and its propulsion (TMI/MOC) stage can be launched intact on one 250 mt ETO flight, thereby eliminating the need for on-orbit-assembly. Thus, three separate cargo flights are launched independently to Mars (as opposed to three cargo landers all on one cargo vehicle). The cargo flights are launched during the 40-day window beginning in November, 2011 by the NTR system. Upon arrival at Mars, the NTR propulsively breaks the entire vehicle into an elliptic orbit from which the cargo MEV de-orbits. The MEV uses aeromaneuvering to reach the martian surface, and uses storable propellants for the final breaking maneuver.
Upon reaching the surface the cargo is autonomously deployed and set-up, and remotely tested to ensure the equipment is functional prior to the first piloted mission launch.
The first piloted flight launches during the next opportunity in 2014. This flight sends a crew of 6 to Mars for a nominal 90-day stay in the Mars system. The mission profile selected for this flight is of the Short-Duration-Stay class, having a 90-day stay-time, with an overall mission duration of 550 days and a "fast"outbound transit of 150 days. This mission scenario has a flyby abort with a flight time of slightly over 500 days as part of its features.
After reaching the surface, all six crew members live out of the lander for up to three days during the check out of the surface equipment sent on the previous cargo flight. The crew members then carry out scientific objectives, both laboratory science and local exploration of the outpost vicinity.
The second crew carries out an approximately 600-day surface stay at a different site than the initial outpost. Since the crew cannot use the existing surface assets from the IOC, the payload for this cargo mission also consists of a habitat, a pressurized rover, a nuclear power plant, a minimal photovoltaic emergency backup power system, an unloader/mover, scientific exploration equipment, and communications equipment. In addition, a two-year surface stay requires considerable supplies; thus, four cargo landers are required to deliver the necessary payload to the surface. The cargo landers are launched to Mars as separate flights as in the IOC.
The NOC six-member crew launches in 2016. The mission profile selected for this flight is of the Long-Duration-Stay class having a 120-day outbound transit, a 648-day stay, and a 90-day return transit, giving an overall total mission duration of 858 days. This mission scenario has a flyby abort that returns to Earth in slightly over one-year as part of its features.
After reaching the surface, all six crew members live out of the lander for up to three days during the check out of the surface equipment sent on the previous cargo flight. The crew members then carry out scientific objectives, both laboratory science and surface exploration. The long surface stay time enables extensive surface exploration in the vicinity of the outpost including geologic field work to interesting sites. A demonstration unit is delivered to conduct experiments in local resource utilization.
For the Mars portion of the architecture, options exist for infrastructure reconfiguration, abort strategies, and schedule flexibility. The precursor mission strategy calls for site reconnaissance orbiters which could be reconfigured as communications orbiters, depending on the orbital constraints. During the first human mission, IOC, an emergency option exists, that is to land the second cargo mission (departed in 2016) at the initial outpost site. The assets available in this cargo mission could be used to supplement the first crew if a longer stay is required. If an emergency situation does not exist, the second cargo mission may still land at the initial outpost site. Returning to the first site allows the next crew to use previous infrastructure, thus expanding the mission facilities or requiring less cargo in the 2016 opportunity.
Schedule flexibility is contained throughout the Mars portion of the Mars Exploration architecture. Following NOC, additional flights are available in 2018 and 2020. These mission opportunities include long stay times and are, consequently, dependent upon the success of the second piloted mission launched in 2016. Finally, the option always exists in this architecture to accelerate the program. The initial Mars mission, scheduled in 2014, could be earlier if the return to the Moon is moved prior to 2005 or the lunar testbed phase proceeds exceptionally well.
Additionally, where the Synthesis Group Report stated a specific implementation (such as the type and number of robotic, precursor missions), that implementation has been followed.
An implementation falls within a functional area and logically follows from the strategy employed within that functional area. Implementations are the very specific method (or tool) selected to accomplish a particular job within a functional area. Implementations lie at the bottom of the hierarchical chain, but are not necessarily restricted to systems or hardware.
Each of the implementations presented below in the functional areas include an overview, a system description, and an operational description. The overview states the reasons why the particular implementation was selected and how the implementation abides by the architecture reference strategy. The system description provides details of the elements supporting the lunar and martian segments of the implementation. The operational description provides a succinct description of the operational characteristics relating to the systems described.
The functional areas included in Section 3 are precursor/robotic missions; science; planetary surface systems; space transportation systems; Earth-to-orbit transportation systems; and telecommunications, information systems and navigation.
The first part of the strategy outlined by the Synthesis Group is to identify and image at least 12 sites from orbit in order to identify hazards that are of approximately one meter in size and to help better understand the terrain types and general surface conditions found on Mars. Additional data types would also be obtained for each of these sites to help discriminate which are of highest scientific interest. From this set of candidate sites, a primary and backup site will be selected based on the dual criteria of scientific interest and availability of a safe location to land and establish a surface base.
The second phase of the strategy is to deploy vehicles to the surface at the primary and backup sites. This vehicle would then perform a number of tasks and gather data that will be used in making a number of key decisions. The first of these tasks is to verify that the site selected based on orbital data does in fact satisfy the criteria for a safe landing and surface base location. The next task is to check the local environment for potential hazards, such as the presence of potentially toxic materials. The third task is to survey the immediate vicinity of the landing site to provide the necessary data to plan for the construction and setup of the surface base. Finally, this surface vehicle will support initial scientific investigations, such as general field work and sample analysis, to assist in planning for the tasks that will be performed by the human crews to follow. Mobility is an obvious necessity of this surface vehicle.
As a result, a number of orbital and surface missions are suggested in the Synthesis Group Report. In keeping with the strategy of minimizing systems and missions, this set is considered the minimum reasonable to support later human flights:
Mars Missions: Site Reconnaissance Orbiters (2) - both 1998 launch
A separate Mars Communications Orbiter (MCO) is launched in tandem with the MSRO. All data acquired by each of the MSRO's are transmitted to the MCO's for relay to the Earth. This allows the MSRO to continue mapping and transmitting data to Earth even if the Earth is not within its direct line of sight. The MCO is estimated to have a mass of approximately 2300 kilograms at launch.
The mission requirements of the MSRO and MCO lead to different orbital requirements at Mars and thus a separation of functions into two spacecraft types. The MSRO will be placed in a low altitude, sun-synchronous orbit while the MCO will be placed in an areosynchronous orbit. A Titan IV/Centaur (or comparable launch vehicle) with an injected mass capability of approximately 7000 kg (15,500 lbs) will be used to launch both vehicles on a single flight.
The MSRO is targeted for an operational mapping orbit that is sun-synchronous at about 4:00 p.m. local time near the equator with a near-polar inclination. This orbit is characterized by a one-day repeat cycle and an altitude of 299 kilometers. After the flight system has been operationally verified in orbit and due consideration given the martian dust storm season, the MSRO will proceed with its primary mission. During this phase, which lasts approximately 20 months, up to 50% of the martian surface will be mapped in the panchromatic, multispectral, and electromagnetic sounding modes at low to moderate spatial resolutions. Of major importance during this period, the two MSRO systems will acquire high resolution maps of at least 12 candidate landing sites for the planning of piloted missions. The combination of the MSRO/MCO systems can meet the Synthesis Group Report objectives to image 12 prospective human landing sites to scale size of about 1 meter.
The primary surface mission is projected to last two years. During the first year, a fairly autonomous rover initially surveys a 10 x 10-km area for surface trafficability, sub-surface obstacles, and elemental and mineral compositions. The site survey is conducted by traversing over the terrain, imaging the surface with stereo cameras and other instruments, sounding the subsurface with electromagnetic sounding (EMS) or radar, and physically probing the surface to about 2 meters with a drive tube to conduct soil tests and validate the EMS data. Within this 10 x 10-km area, the rover more intensively surveys nine 100 x 100-m sites for selection of locations for a power plant, a habitat, and a landing site for human missions. There is also time for sample selection, collection, and caching. During the second year, the rover could be used to explore regionally outside the 10 x 10-km area for useful resources and to collect and cache more samples. The rover could be either more or less autonomous in this phase, depending on how much interaction is desired.
An extended mission could last nearly two years, considering the planned four-year length of the rover's primary mission. During this period, a rover would continue to explore regionally. The rover would probably be used in a more autonomous mode in this phase to minimize interaction while the next rover is being supported in its primary mission.
This same pattern would be repeated for the second rover in the next launch opportunity (August 2005) landed at the selected back-up site.
Orbital science includes using humans as operators of instrument platforms, e.g., instrument cycling, repair, and manual contingency operation. In addition, humans as observers in orbit can provide direct visual observations of physical features occuring on the planet's surface. Further, humans in orbit can teleoperate instruments and rovers on the planet surface without the delay times incurred from teleoperations from Earth. In addition, a wide variety of remote sensing of the Earth, Moon, and Mars can be done from orbit.
Common Lunar Science Studies: The Synthesis Group Report summarizes five areas of lunar science that will be accomplished to some degree by each architecture. The Moon is to be used as a target of study, i.e., for geosciences and tenuous atmosphere. Additionally, the Moon will be used as an observatory platform from which telescopes and sensors can measure and record astronomical phenomena and particle fluxes. The lunar soil will be studied for its historical archive of solar and geologic information. The regolith will be studied for its building materials and energy potential.
Finally, excursions on the Moon will be used as a simulant for Mars terrains for geosciences field work, and experience in traversing and operating on a planetary surface.
Common Mars Science Studies: Surface Science: 30-100 days The Synthesis Group Report specifies that as surface capabilities are enhanced, the Mars surface will be characterized at progressively greater distances from the landing site, and in increasing detail. During the 30-100 day missions the site is characterized at 2, 50 and finally a maximum of 100 kilometers. Field studies are conducted by a combination of humans and robots. A pressurized rover capability enables more distant access for humans, increasing to 50 - 100 km. During the longer pressurized traverses a crew of 2-3 people explores key geologic sites, collects samples, deploys instruments, and does field work.
During this phase, there are small-scale resource-for-fuel feasibiltiy experiments.
Surface Science: 600 days With the advent of longer Mars stay-times the crew is able to conduct more thorough field work and revisit sites of scientific interest if necessary. A modest geochemical laboratory enables some rock/exobiology sample analyses including bulk examination, chemistry, mineralogy, and volatile concentrations.
Meteorological and environmental measurements are made, studying such parameters as seasonal climate variations and dust storms.
Long-term studies of complex scientific issues are initiated such as the search for life, the study of ancient climates and past physical processes which formed and molded the planet.
Exploratory observations are enhanced by robots deployed at diverse locations, which are then controlled from the Mars landing site or Mars orbit. There rovers can do field work, deploy instruments, and take and deliver samples for high grade and Earth return.
Scientific investigations build on data and advances catalyzed by previous Mars missions.
The second 14-day mission in 2006 delivers a small science payload and allows some time for reconnaissance exploration and scientific investigations near the landing site and local areas of interest within 2 km.
Science and exploration is divided between two teams. The first team consists of two crewmembers exploring using the unpressurized rover. Small instruments such as a geophysical station, small automated telescope, and space physics drop-off package are ferried and deployed near to the site, but away from launch/landing operations; these are carried on the unpressurized rover.
The second team of two explores the near-outpost on foot, sampling, observing and conducting a teleoperated rover from the outpost simultaneous to the human traverses.
The fifth crewmember remains in the habitat for mission safety, control/operations, and communications.
Doing as many EVA expeditions as possible, "minimum-requirements" geology traverses and sampling are emphasized, balanced with the equally important simple instrument deployment.
Science payloads and delivery schedule for this and other lunar IOC/NOC phases are listed in Figure 3.2-1. Two tables showing (1) science payload mass versus mission phase, and (2) science instruments delivered versus mission phase are presented in Figures 3.2-2 and 3.2-3, respectively. Detailed mass, volume, power, and data parameters for science payloads are listed in Appendix B.
Lunar NOC-1: During the 45-60 days of the Lunar NOC-1, the crew "evaluates the pressurized rover including the telerobotics...[and does] meaningful science in the process.." This is taken to mean that the crew evaluates the strategy of surface operations and exploration, using both a pressuirzed rover and teleoperated rover. At the same time, as much exploratory science is completed as possible.
The additional capability of pressurized exploration greatly enhances the potential science return by increasing time in the field and access to planetary environments. A typical two-week pressurized excursion is described:
Meanwhile, back at the outpost, concurrent science activities continue. Some basic sample analyses are done to high grade samples collected thus far. Science systems and operations are evaluated, as well as the exploration strategies and techniques. If necessary, upcoming excursions are redirected as new scientific data and input are continually integrated into the science plan.
Lunar NOC-2: Science activities during the Mars dress rehearsal are divided between the time spent in lunar orbit and the time spent on the surface. The long duration of the mission provides important life sciences data.
While in orbit, the crew is to accomplish meaningful science while gaining experience using remote sensing and telerobotic systems. Remote sensing and imaging of the Earth and Moon is accomplished with appropriate sensors on the MTV Hab Module. Sensing the lunar surface augments geochemical and topographic maps and provides more detailed science and resource data at sites of particular interest.
In order to conduct an authentic Mars simulation, a teleoperated rover capability is required on the lunar surface. To maximize access, it is suggested that a rover be deployed to a site that is geologically interesting but not intended for human exploration. This provides crew experience in teleoperations while collecting real surface geologic and geophysical data that would be otherwise unavailable. The alternative is to deliver the rover to the outpost on the 2008 cargo flight. Later this rover can be teleoperated from the landing site.
During the 30-day surface stay a science program is executed that closely approximates what the crew would do at Mars. An attempt is made to choose sites, strategic approaches and investigations that are relevant (at least operationally) to those to be done on Mars. The crew, equipped with a pressurized rover and exploration equipment, conducts pressurized and unpressurized traverses and deploys instruments as before. They collect samples, do traverse science, conduct active seismic experiments, and do a 10-meter drilling test. At the outpost, the crew conducts local traverses, deploys instruments, does basic sample analyses, and conducts plant/animal/human biomedical experiments in the small laboratory.
The "clean-up crew" that remains on the Moon for 90 days to monitor mission systems also continues to do meaningful science and pressurized rover trips after the first crew departs.
Again, specific science payloads and delivery schedule are shown in Figure 3.2-1.
Mars IOC: The Synthesis Group Report indicates that crewmembers will arrive at Mars and accomplish scientific exploration of the surface. Science activities are categorized in three phases: cruise science, orbital science, and surface science.
Cruise science is done during each human mission, and consists of experiments that will be carried out en route during the prolonged transit to and from Mars. The science payloads are confined to the MTV and are never deployed to the Mars surface. For this reason they are listed as a separate mass total (see Appendix B). Cruise science experiments include solar, particle and astrophysics, human biomedical research, sample analyses (return trip) and Principle Invesigator (PI) experiments.
Orbital science is conducted from Mars orbit primarily if the mission is aborted before landing. Actvities include telerobotic science, remote sensing, and human observations. To maximize the scientific return of such a failed mission would require the contingency measure of a teleoperatable rover that could be soft landed to the surface and operated from orbit.
Once on the Mars surface, the crew has 30 to 100 days to do outpost science and exploration. Activities are balanced between local exploration and 2-3 pressurized traverses. A geophysical monitoring station is deployed near the outpost which is also equipped to monitor meteorological phenomena. EVA's, both local to the outpost and during pressurized excursions, do reconnaisance geology , traverse geophysics, sampling, and search for traces of past life. Special attention is given to understanding the Mars geomorphology, erosional features, fate of past water systems, and depositional environments responsible for sedimentary patterns.
Active seismic experiments are conducted to unravel the subsurface structure and composition, and, for the first, time a drill spirals into the martian strata.
A modest analytical laboratory allows for examination and chemical analyses of sediments and rock samples. Sediments are likewise tested for organic content and volatiles.
A biomedical laboratory allows for experimental research on human response and performance on low gravity planetary surfaces.
Later in the mission, a collection of more advanced dedicated meteorological instruments are deployed in a facility that will include launching of weather balloons to test the chemistry, physics and structure of the martian atmosphere.
Additional basic research is accomplished through discretionary Principal Investigator (PI) science experiments which are deployed and operated on the surface.
Science payloads for Mars IOC/NOC are also shown in Figure 3.2-1. Two tables showing (1) science payload mass versus mission phase, and (2) science instruments delivered versus mission phase are presented in Figures 3.2-4 and 3.2-5, respectively. (The science instrument icon key for Figure 3.2-5 is given in Figure 3.2-3(b).) Detailed mass, volume, power, and data parameters for Mars science instruments are provided in Appendix B.
Mars NOC: Research conducted during Mars NOC is an elaboration and refinement of Mars IOC, and builds on the science framework of discoveries and hypotheses established as a result of the previous Mars IOC. The most complex scientific puzzles can now be tackled and pieced together. Elusive phenomena requiring long-term observing are monitored. Cruise science in-transit and orbital science are conducted as before.
On Mars, increased surface access combined with longer stay-time greatly enhances the science return. A diversity of environments can be visited and observed. More time is available for detailed geologic observations, real-time contemplation, experiential analogs and additional discoveries in the field. Very important return visits to strategic sites are now possible.
The past two years (that is, Earth years) of meteorological monitoring data provides a reliable base for further observations, and human crews will now experience and record first-hand the seasonal changes of another two-year weather cycle.
Multiple robots deployed at diverse locations can be controlled from the Mars landing site (and/or orbit) to conduct reconnaisance geology, collect and/or analyze samples, deploy simple instruments, and do traverse geophysics.
The Synthesis Group Report suggests a different landing site may be chosen for the Mars NOC outpost. This would additionally enhance the science return as a result of increased local exploratory opportunities in the vicinity of a different Mars environment.
Two separate outposts are also emplaced at Mars. The first supports a 90-day crew stay. The second, located at a different site in order to provide science data from an area geologically distinct from the first, supports a 600-day crew stay.
Lessons learned on the Moon are used in the development of Mars systems. Since the environments of the two worlds are radically different, the systems used will be different. Commonality is maintained in the form and function of the systems; for example, the habitats used on the Moon and Mars will employ pressure shells of the same dimension and will have much the same interior layouts, but will differ in their life support and thermal control systems.
Habitation: A single, integrated habitat which can support 5 crew for 14 days is provided. The habitat is a Space Station Freedom (SSF)-derived cylindrical module, with an airlock attached to one end and a docking adapter on the other end. Due to the down-mass limitations of the cargo lander, the module is two-thirds the length of a full SSF module, with length 8.2 meters and diameter 4.5 meters; its mass is 23 mt. Two such modules are needed to meet the crew requirements of the later lunar missions. (A single, fully integrated module for 6-crew missions of up to 90 days would weigh approximately 40 metric tons; this weight would exceed the capability of the lander.)
The pressure shell is essentially identical to that of a SSF module, with leveling legs and deployable regolith shielding retention devices. Internal systems of the habitat include life support, thermal control, power management and distribution, crew accommodations, limited health care equipment, science accommodations, and utilities distribution. The life support system is an advanced SSF regenerative system, with greater than 98% oxygen recovery, hygiene water processor, and non-expendable water polisher/bacteria barrier. Thermal control is provided by coatings, heat pumps, and composite reflux radiators with a two-phase non-toxic working fluid.
The airlock is a SSF-derived system which enables egress/ingress and also provides EVA suit storage, checkout, and recharge. The airlock system is composed of an equipment lock, a crew lock, an EVA dust-off porch, and adjustable legs for leveling. The airlock's life support and thermal control systems are tied into the habitat. The EVA dust-off porch is side-deployed, and a docking adapter for later use by the pressurized rover is attached on the end opposite the habitat (see Figure 3.3-1). Ideally, the airlock is delivered pre-attached to the habitat, in order to avoid the difficult operation of connecting the two in-situ.
Power: A photovoltaic array (PVA) with regenerative fuel cells (RFC) for nighttime power is used for IOC. The array consists of 150 m2 of sun-tracking panels. The cells are of amorphous silicon. The system provides 25 kW during the lunar day and 12.5 kW at night. It is sized to power the habitat and provide recharge power for the rover and unloader. During this phase, a minimal battery system is included in the habitat which would, in case of failure of the primary system, provide keep-alive power to the habitat until repairs or replacement could be performed, and also allow the crew ample time to vacate the outpost. The PVA/RFC system also provides standby power to the outpost during periods in which there is no crew on the surface.
Extravehicular Activity: Extravehicular Mobility Units (EMU) are provided for each crew member on the lunar surface. An EMU consists of a pressure suit, a Portable Life Support System (PLSS), and communications subsystem. The suits are of back-entry, hybrid (fabric and hard components), 5.85 psi design. The PLSS is a regenerable system which provides for 8 hours of EVA. EMU accessories include helmet-mounted video cameras and lighting systems.
Communications: Radio frequency equipment and associated electronics are integrated into the habitat. A deployable tower and dish antenna are located near the habitat (they might remain on an expended lander). The system provides UHF communications to and from the tower, satellite communications (Ka band) to Earth, S-band communications to the landers, a LORAN-type means for navigation of surface rovers and landers (within 12 km of the outpost), and internal habitat communications.
Surface Transportation: A six wheeled, unpressurized rover is provided. The rover can seat 4 suited astronauts, or can carry two together with a removable, self contained extended life support package. The segmented chassis is composed of a light weight tube framework, with independent drive on each wheel. Power is provided by regenerative fuel cells, which are recharged from the base's power system. Thermal control is provided by a heat pump with metallic reflux radiators, enabling the rover to operate anytime during the lunar day. The range of the rover is 50 km from the outpost, or 150 km total traverse.
A multipurpose construction vehicle is also provided. The Lunar Excursion Vehicle Payload Unloader (LEVPU) is a three-strut, cone-wheeled, teleoperated gantry crane. It is capable of unloading cargo from the lander, transporting cargo (up to and including an integrated habitat), and emplacing elements on the lunar surface. A set of implements and attachments designed for its 3-joint manipulator arm enable the LEVPU to perform various other tasks, including light excavation (e.g., boulder clearing, regolith smoothing, and/or trenching), and precision surface element alignment and attachment. The choice of a LEVPU plus attachments avoids the need to deliver several specialized construction vehicles. The LEVPU's primary structure consists of open web, aluminum alloy members with telescoping struts, and independently driven and controlled wheel assemblies. The power and thermal control subsystems are similar to those on the unpressurized rover.
Launch and Landing: A small verification unit for demonstrating the storage of cryogenic liquids on the lunar surface is emplaced and operated at the initial outpost. It operates autonomously with monitoring from Earth, and conducts tests of systems to control cryogen boiloff by the use of thermodynamic vents, vapor cooled shields, low conductivity supports, and refrigeration and reliquifaction equipment.
Science Accommodations: Limited crew time, power, and habitat volume is available for science activities. However, the LEVPU can deploy scientific instruments on the lunar surface, and the unpressurized rover can be used for geological traverses.
Other: In addition to the systems described above, a warning system for solar flares is also emplaced near the habitat. It consists of an autonomously controlled system for monitoring the particle and electromagnetic output of the sun. Threshold alarms are included which alert the crew when the incident solar radiation exceeds a predetermined value, so that they may take shelter until the flare subsides. This system is a backup to solar monitoring stations on the Earth and in space.
Consumables pallets are delivered on each crew flight. Consumables include food, life support expendables, clothing, hygiene supplies, and housekeeping items. The pallets provide power, monitoring, pressurization, and thermal control where required for the consumables.
Habitation: During this phase, a second habitat/airlock unit is emplaced. It is externally identical to the initial habitat and is connected to the adapter on the end of the habitat away from the airlock (see Figure 3.3-2). Its critical internal systems can operate independently of the initial habitat, providing separate pressurized volumes in case of difficulty in either habitat. It differs only in its internal outfitting: crew quarters, galley, etc., are located in the initial habitat, while the second habitat contains an expanded crew health care facility, scientific accommodations, and storage space for the consumables required during long term (30-90 day) missions. With the addition of this second habitat, and the emplacement of the requisite regolith shielding, the outpost can now support 6 person crews for up to 90 days.
Power: The power capability of the outpost is upgraded by the emplacement of a 100 kW nuclear power system. The system consists of an SP-100 reactor fitted with 4 Stirling engines (2 in use, 2 in reserve), providing 100 kW of electrical power continuously. It is designed for easy deployment, with little or no human intervention required. Limited shielding is provided on the reactor to enable short-duration proximity operations by humans. Additional shielding is provided by placing the reactor in a pre-excavated hole. The system is fully autonomous and employs fault detection, isolation, and recovery systems which result in a reliable, long-lived (nominal 15 year lifetime) unit. The existing PVA/RFC system is maintained as a backup.
Surface Transportation: A pressurized rover system is delivered for use in this and subsequent phases. The pressurized rover itself has limited capability (on the order of 50 km from the base), but with the addition of an auxiliary power cart and an experiment/sample trailer, this is extended to a range of 100 km from the base, for 2 crewmembers for up to 6 days. The rover has twin manipulator arms for geologic sample collection and IVA access to surface equipment. Power is provided by regenerative fuel cells; thermal control is provided by coatings and a 2-phase heat pump. The life support system is partially closed with storage of wastes for return to the base.
Science Accommodations: Expanded science accommodations are available in the second habitat. The pressurized rover extends the range of surface exploration.
Habitation: No extra habitation volume is added to the existing outpost. Emplacement of an appropriate Mars simulation requires replication of the existing linked-habitat outpost at another site on the lunar surface. Due to the size of the crew (6), and the duration of the simulation (30 days), both habitats are needed. The habitats are nearly identical to those delivered to the first outpost. They will, however, differ in the life support system used: the Mars simulation will utilize the same life support technology as will be used for the Mars mission. In this implementation, that is an advanced SSF regenerative system which incorporates waste processing in order to reduce consumables usage.
Power: PV/RFC and nuclear systems identical to those at the original outpost are used at the Mars simulation site. The operation of emplacing these systems also enhances the fidelity of the Mars simulation. It should be noted however that Martian power systems will differ greatly from lunar designs. For example, the PV array will be much larger, and the RFC system much smaller, at Mars. Thermal control for all systems will also be different at Mars. This means that the simulation is a test of operations, not of Mars hardware.
Communications: The communications system delivered to the outpost for IOC is duplicated at the Mars simulation site.
Surface Transportation: The simulation crew brings an unpressurized rover like the one described previously. They use the pressurized rover delivered to the base during NOC 1. The payload unloader from the initial outpost is also used at the simulation site, to reduce cargo requirements.
Figure 3.3-3 schematically depicts the layouts of the two lunar outposts.
Habitation: The need to support 6 crew for 90 days, together with the down-mass capability of the Mars landers, dictates that the martian habitat be delivered in two pieces. As in the lunar case, a single habitat capable of fulfilling the mission requirements would weigh approximately 40 metric tons, but this is divided into packages of 23 and 25 tons to accommodate the capabilities of the lander.
The habitats and airlocks are similar to those described in lunar NOC 1. A different thermal control system is used on Mars due to the different thermal environment, in particular, the cooler daytime temperatures. Differences in the life support system are discussed in Lunar NOC 2.
Current information indicates that radiation shielding, beyond that provided by the martian atmosphere, will not be required.
Power: A 100 kW nuclear system is used for primary power, with a 25 kW PV/RFC system as backup. The nuclear system is similar to the lunar system, but has a slightly different thermal control system. The PV/RFC system has a much larger photovoltaic array, due to the reduced solar flux at Mars, but also has a much smaller fuel cell system, because of the significantly shorter martian night.
Extravehicular Activity: EMU's are provided for each crew member. The martian EMU differs from the lunar model only in the PLSS. Due to the greater gravity of Mars, it may be necessary to use a mid-EVA, 4 hour recharge to reduce the mass of the PLSS.
Communications: The communications system is also similar to that employed on the Moon, but depends on an orbital relay network for continuous communications with Earth.
Surface Transportation: One pressurized and one unpressurized rover similar to the lunar models are used. A power cart and sample trailer are also delivered as in the lunar case, to extend the range of the pressurized rover.
Since the Mars lander design delivers the payloads closer to the surface than does the lunar lander, a downsized payload unloader is used. It is a four-legged gantry crane with systems otherwise similar to the LEVPU, but this smaller (shorter) device accommodates payloads delivered by the lander to within one meter of the surface. Like the LEVPU, it is delivered with a set of attachments which allow it to perform simple site improvements and manipulation tasks.
Other: A flare warning system identical to that used on the moon is also provided at the Mars outpost.
The Mars IOC outpost layout is shown in Figure 3.3-4.
Habitation: Since 1) the crew cannot use the existing surface infrastructure, and 2) the habitation and consumables storage requirements of a nearly 2-year mission are considerable, an additional hab/lab/storage module is required, beyond the two module system used in IOC. This module contains expanded crew habitation, science racks, and consumables storage. In this case, the three modules are connected in-line, with airlocks at both ends. (see Figure 3.3-5)
Power, Extravehicular Activity, Communications, and Surface Transportation: Power, EVA, communications, and surface transportation systems are identical to those used at the first Mars landing site.
Other: A Mars ISRU demonstration package is emplaced and operated. It combines demonstrations of technologies for extracting water from the martian atmosphere and regolith, and producing oxygen and methane from the atmosphere.
Local geological exploration is carried out near the outpost and via the unpressurized rover, as time permits. A geophysical monitoring station is deployed within walking distance of the outpost.
At the completion of the 14 day stay, the crew places the habitat in standby mode and departs.
The crew also supervises the excavation, by the payload unloader, of a hole of the proper dimensions for emplacement of the nuclear power supply during the next phase.
As did the first crew, this crew places the base on standby and departs in the lander near the end of the (14 day) lunar day. The completion of this mission, and the emplacement of a viable lunar outpost, marks the achievement of Lunar Initial Operating capability.
After occupying the base, the crew connects the nuclear power supply to the base power distribution system, then checks out and (remotely) activates the reactor.
The crew uses the pressurized rover to explore the vicinity of the base and select suitable candidate sites for the Mars simulation. Science operations are carried out as part of this activity as maintenance and contingency requirements permit.
Verification of an operational base which can support 6 crew for 60 days, and location of an appropriate Mars simulation site within a few kilometers of the base, marks the achievement of Lunar Next Operational Capability 1.
The simulation outpost is remotely monitored for approximately one year prior to the arrival of the simulation crew, to evaluate the feasibility of delivering systems to the surface of Mars two years before they will be depended upon by human explorers.
All operations are carried out while a support crew is occupying the first outpost. The support crew lends assistance as necessary to complete the simulation. At the end of their 30 day stay, the simulation crew may power down and safe the simulation outpost, or this may be left to the support crew.
The completion of the Mars simulation marks the achievement of Lunar Operational Capability 2. There is an opportunity for further tests of Mars systems and operations in 2010 and 2011, if necessary, before the first actual cargo is launched to Mars. What is done with the substantial assets of the two lunar outposts is a subject for further study.
The unloader prepares the outpost site, then emplaces all systems. This requires that the unloader operate with a high degree of autonomy, due to the round-trip communication delays between the Earth and Mars. Once all systems are located in their final positions, Earth ground control verifies their integrity to the degree possible, before committing a Mars crew to trans-Mars injection. The systems are monitored throughout the crew Mars transit, and if needed, contingency operations are planned for the crew to execute on arrival.
At the end of the surface stay, the crew places the outpost systems in low-power standby mode, then departs. Completion of this first human mission to Mars marks the achievement of Mars Initial Operating Capability.
The ISRU demonstration unit is also deployed by the unloader. It operates autonomously with supervision from Earth.
At the end of the 600 days, this outpost is also placed on low-power standby, and the crew departs Mars. The completion of a long-duration Mars surface stay marks the achievement of Mars NOC.
Lunar Cargo Capabilities: Figure 3.4-1 shows that the cargo capabilities range from approximately 21 mt on a piloted mission to 41 mt on a cargo-only mission.
Lunar Mission Initial Mass in Low Earth Orbit (IMLEO): The IMLEO's of the reference vehicle correspond to the cargo capabilities given. The IMLEO's for each HLLV launch are presented in Figure 3.4-2. For both cargo and piloted missions, the trans-lunar injection (TLI) stage is launched on the first HLLV, and the rest of the lunar vehicle is on the second HLLV launch. The TLI stage requires the full 150 mt capability of the launch vehicle; however, the remainder of the lunar vehicle, for both piloted and cargo missions, utilizes approximately 120 mt of the 150 mt launch capability of the second launch.
The TLI stage requires five RL10 derivative engines, makes use of an advanced integral cryogenic reaction control system for attitude control and stabilization, and utilizes aluminum-lithium and graphite-epoxy materials for the structures and tankage. The thermal control system is designed to provide boiloff management for up to 60 days in LEO. Advanced, man-rated, redundant avionics and communications capabilities are provided. Electrical power is supplied by batteries and fuel cells.
The LOI/TEI stage requires three RL10 derivative engines and utilizes common hardware and software design elements with the TLI stage to the extent practical.
The LEV requires five throttleable, RL10 derivative engines with an integral cryogenic RCS for control and stabilization. The structure and tankage makes use of Al-Li and Gr-Ep materials. The LEV and the LTV share common system designs for some elements, including the main engines, RCS thrusters, avionics, and communications. Four advanced fuel cells provide the electrical power for short duration missions. Landing legs and pads are provided for surface clearance and landing in unimproved areas. The thermal control system, utilizing a partial thermal tent, maintains the propellants during short mission stays on the lunar surface. For long durations on the lunar surface, surface system power and thermal conditioning are required.
Several key technologies for the LTS are inherent in this architecture, including cryo-fluid management, automated rendezvous & docking, advanced structural materials, throttable cryogenic engine, and automated precision landing.
Two ETO launches are required to perform each of the missions (cargo and piloted). The TLI stage is launched first, followed 30 days later by the launch of the rest of the LTS. The HLLV incorporates an integral kickstage that is used to circularize the HLLV payloads. In considering these long stays (30 days) in LEO, several operational implications need to be addressed. Orbital maintenance and station keeping, boiloff of cryogenic propellants, man-made orbital debris and micro-meteoroids impacts are the major concerns. With orbit maintenance and station keeping, concerns of propellant utilization become dependant on stay duration and the total number of maneuvers needed during stay. Boiloff of the cryogenic propellants is a factor in determining the size of the tanks and the thermal protection system used or the amount of propellant that must be transferred for resupply. Man-made orbital debris is a by-product of long duration stay in orbit, and proper effective ways to dispose of or deal with it must be considered. The longer the stay in orbit, the more exposure the vehicle and the crew undergo to such things as radiation and micro-meteoroids. The effects of these conditions must be accounted for in all aspects of the vehicle design and mission operations.
The five piloted missions all carry six crew members; however, the 2005 and 2006 missions leave one person in orbit while the other five descend to the lunar surface. This scenario requires two crew modules and increases the size, power and consumables required for each module since they are both inhabited. The lander will maintain itself for the first two weeks on the surface. After that, it is assumed that surface power and cryo refrigeration units will maintain the lander for the rest of the surface stay time. The longer stay times for the later missions will have some effect on the LOI/TEI stage since it is not sized for up to 90 days of boiloff; however, it can be assumed that enough about cryofluid management will have been learned that the LOI/TEI tanks can be easily modified, probably by changing the thermal protection system, to accommodate these missions.
The Mars piloted vehicle is shown in Figure 3.4-8. It uses nuclear thermal propulsion for all major maneuvers. The core configuration includes two NTP engines at 75,000 lb thrust each, a radiation shadow shield, an aft tank assembly, an interstage structure that includes expendable tank attachment and connect provisions, the Mars transfer crew habitat, power, thermal control, attitude control and communications utility services, and the Mars excursion vehicle. The core configuration is launched in two 30-meter-length sections on the 250 mt nominal payload capability HLLV. Additional hydrogen propellant is provided by expendable hydrogen tanks launched separately and berthed to the core vehicle in low Earth orbit.
The Mars cargo vehicle is shown in Figure 3.4-9; it uses the same nuclear engine as the piloted vehicle, with one per vehicle since engine-out is not required. Each cargo vehicle consists of a nuclear stage which delivers the cargo MEV to Mars orbit and one cargo MEV. This arrangement permits each cargo vehicle launch to be all-up with no Earth orbit operations required. The cargo vehicle is derived from the piloted vehicle, applying subsystems as needed.
The Mars Transportation System for both piloted and cargo configurations is comprised of a Mars Transfer Vehicle (MTV) and a Mars Excursion Vehicle (MEV). The MTV and MEV are described below for the piloted vehicle configuration. The MTV and MEV for the cargo vehicle configuration would be similar, but not include the transfer habitat or crew module.
Mars Transfer Vehicle Description - The nuclear engines characteristics used in this implementation are a thrust-to-weight ratio of ten or greater. Isp is baselined as 925 seconds. Liquid hydrogen propellant is provided by vehicle tanks; warm hydrogen gas is routed from the engines to the tanks for pressurization during burns. Vehicle tanks are thermally insulated with multilayer insulation and vapor-cooled shields; active refrigeration is not used. Both engines are operated for all maneuvers unless one is inoperable. Mission rules provide for return-to-Earth abort in the event an engine fails.
Attitude control propulsion is provided by mechanically compressed hydrogen gas obtained from main tank boiloff. Hydrogen gas accumulators provide sufficient storage for any one auxiliary propulsion maneuver; the accumulator capacity is sized by Earth-Mars leg midcourse correction requirements. Accumulators are recharged during coast periods. Nuclear engines have low-rate gimbal capability for center of gravity tracking; the attitude control propulsion system provides attitude damping during thrust periods.
Propellant tanks are aluminum-lithium alloy. Intertank and other main structures employ advanced composites for reduced mass. The interstage uses a simple telescoping arrangement to reduce vehicle length during launch. The extended length of this structure is sufficient to allow for attachment of the expendable hydrogen tanks. The transfer habitat is a composite-reinforced aluminum pressure vessel with metallic interior secondary structures.
Thermal control is provided for the transfer habitat and externally-mounted utility services. Cryogens are insulated as noted above. Nuclear engines provide their own thermal control except after-heat removal which is provided by hydrogen bleed flow from the main propellant system.
All electrical power is provided by a solar array/advanced battery system rated at 27 kW average power. Batteries provide power during propulsive maneuvers and solar occultations. The system is operated at a de-rated level while parked in LEO so that LEO operations do not dictate power system capacity.
The avionics system is located in the transfer habitat, except for MEV and CRV avionics, RF power amplifiers for the high-gain antennas, and distributed data acquisition and controllers. The avionics system is multi-string and includes vehicle health management functions as well as crew controls and displays. Commonality across avionics systems is maintained to the extent practical, but each vehicle has special functions such as approach ranging for the interplanetary vehicle and landing radar for the MEV.
The environmental control and life support system for the transfer habitat is a physical-chemical two-gas system closed on oxygen and water. Food is supplied in shelf-stable and frozen forms. A greenhouse is provided for modest fresh vegetable supply but its products are not required for crew health/survival. The ECLSS is redundant as is the pressurized volume of the habitat so that a depressurization only affects half the pressurized volume; recovery and repressurization means are provided. The ECLSS systems for the MEV and CRV are open-loop in view of the short mission duration for these vehicles. The MEV is capable of supporting its crew for up to 5 days while the surface base is checked out and during ascent to Mars orbit at the end of the mission.
The transfer habitat provides full-service crew systems with private quarters, a galley/ wardroom, command and control area, health maintenance, exercise and recreational equipment and space. Dedicated radiation shielding is not provided; radiation dose calculations indicate that the shielding provided by the transfer habitat structure, systems and consumables may be adequate to protect the crew from galactic cosmic rays and solar proton events (SPEs) assuming the crew uses the galley as a storm shelter during severe SPEs. However, further analysis is required to firmly establish shieldiquirements. Radiation analyses indicate the MEV and CRV do not require radiation shielding; this assumes a warning system capable of forcasting approximately 24-hour SPE "safe" periods for MEV ascent. Crew system provisions in the MEV and CRV are similar to those provided by the Apollo command module.
Mars Excursion Vehicle Description - The MEV performs the descent and ascent maneuvers for the piloted Mars missions, and the descent cargo delivery for cargo-only missions. For the cargo-only missions, the MEV does not have an ascent stage. Descent from Mars parking orbit is performed using an aerobrake to slow down from entry speed to about 600 m/sec; final deceleration and descent use rocket propulsion. Descent and ascent propulsion systems are separate, using storable propellants. The same engine design is used for descent and ascent. The MEV cargo delivery capability is 45 mt in the all-cargo mode and 11.5 mt in the crew mode.
The propulsion characteristics of the MEV are:
Propulsion - The ascent and descent main propulsion systems use pump-fed gas generator storable propellant engines. The descent propulsion system has engines distributed around the periphery of the descent stage to permit cargo to be close to the surface of Mars after landing. This leads to a limited engine-out capability; if an engine fails, a balancing engine must also be shut down. The presumed mission rule will be that unless all engines start successfully for the initial deorbit burn, a landing will not be attempted. If an engine fails during or after landing engine restart, an abort to orbit is possible with the ascent stage.
The ascent propulsion system uses the same type of engines, but clustered beneath the ascent stage center of gravity for full engine-out capability.
RCS/Auxiliary Propulsion - Each stage of the MEV has its own RCS/auxiliary propulsion system; these consist of self-contained pressure-fed storable propellant/thruster modules.
Aerobrake - The aerobrake is a multi-petal folding rigid design. Advanced composite materials are used for minimum mass. The heat shield/outer shell is titanium-aluminide with a zirconia overspray. The relatively mild heating environment for deorbit/descent requires only modest thermal protection; the brake is designed with enough thermal mass and structural redundancy to survive worst-case boundary layer leakage through petal seams. The aerobrake is deployed in Earth orbit after launch and remains deployed throughout the mission. During Mars descent, after the entry heat and aerodynamic pressure pulse, doors in the brake open and descent engines are started. As the MEV slows down under rocket thrust and as aerodynamic pressure continues to decline, the aerobrake is jettisoned. Landing occurs on rocket thrust.
A lightweight deployable wake-heating fairing protects the cargo and/or ascent stage during descent. This fairing is deployed just before the deorbit burn and jettisoned on descent after the aerobrake.
Thermal contro l - Thermal control of the crew module is provided by a simple single-loop system with body-mounted radiators. The system has limited water-boiler heat-sink capabilities for the descent period when the wake heating fairing is in place. MLI and electrical heaters are used to maintain storable propellants in the desired temperature range.
Structures - Propellant tanks are aluminum; the advantages of advanced tank materials are very limited for this small vehicle. Dry structures use advanced composites for minimum mass. The descent stage structure is designed around the cargo-version payload envelope (8 meters diameter x 11 meters length) and the aerobrake, with a removable section at one end, such that the payload can be lowered onto a transporter and moved from under the MEV. The ascent stage structure is a simple truss arrangement that interconnects the propellant tanks, propulsion system, and crew module.
Electrical Power - Electrical power for active periods (descent and ascent) is provided by advanced primary batteries. During dormant, powered-down periods on Mars, health maintenance power is provided by a small solar array/battery system.
Avionics - All avionics except descent-unique functions and distributed sensors, effectors and data multiplex/control units, is contained in the crew module. The avionics system is multi-string and includes vehicle health management functions as well as crew controls and displays. RF communications links with the MTV and surface base are provided; a backup voice-only and low-rate telemetry link direct to Earth is also provided.
ECLSS - The ECLSS system is a simple two-gas open-loop system with LiOH CO2 absorption. Food is provided in ready-to-eat form. Hygiene is Apollo-style. The crew wear EVA suits during descent and ascent; these provide backup for accidental cabin depressurization. All cabin systems (except the obvious ECLSS functions) are designed to operate normally in vacuum. The entire cabin can be depressurized for egress and ingress; if an IVA crew transport module is available on Mars for later missions, a hatch connection for it can be added to the MEV.
Crew Systems - Interior crew systems consist of seats, windows for descent piloting, and flight controls and displays. The ascent stage crew module is used for descent to enable descent abort to orbit. An ingress-egress hatch at the top of the crew module includes a berthing adaptor for IVA transfer to/from the MTV crew habitat; a similar hatch and stairway in the side of the module near the planet surface provide for on-surface ingress and egress. No solar flare shielding is provided. Since the ascent and rendezvous sequence can require up to 36 hours, a limited capability to predict flare-safe periods is assumed.
The part of the vehicle launched first includes teleoperation arms for berthing the following vehicle elements. These are equipped with automated rendezvous and proximity operations packages to fly to within reach range of the arms. Vehicle assembly occurs autonomously, assisted by ground-based teleoperation as needed. Debris shields are launched attached to collision-sensitive parts of the vehicle such as propellant tanks, and removed before TMI by a cargo transfer vehicle (CTV).
About one month before the TMI window opens, a test crew will board the vehicle for final tests and pre-orbital-launch checkout. One week before the window opens the mission crew will board; after a tie-in period the test crew will return to Earth on the shuttle that delivered the mission crew.
Trans-Mars injection occurs in three burns of the NTP system. The first burn places the vehicle in a 72-hour elliptic orbit with apogee about halfway to the Moon's orbit. The second burn occurs at apogee and makes the plane change required to access the trans-Mars velocity vector; orbit period is not changed by this burn. The third burn starts just before perigee and increases the vehicle velocity to that required for TMI. The crew spends the time during the first and third burns in the galley area to reduce radiation dose from van Allen belt passage.
Trans-Mars injection tanks are retained during the coast to Mars for their radiation shielding value. Midcourse corrections during trans-Mars are divided into three maneuvers to reduce total delta V, improve targeting, and also reduce the amount of hydrogen that must be stored in the attitude control propulsion system accumulators.
A few days before Mars arrival, terminal navigation and maneuvering begin. Navigation can use satellites in Mars orbit or radar ranging of Mars itself for approach state vector update. A test of the nuclear engines assures that both are ready for operation; if a failure is detected, or if other mission/equipment anomalies dictate, the approach path is retargeted by the attitude control system for a Mars flyby abort.
The Mars phase of the mission begins with a single-burn orbit insertion into an elliptic orbit. The state vector is updated by Earth track, and descent preparations begin, including orbital high-resolution imagery and viewing of the planned landing site. The MEV is checked out. Separation and de-orbit of the MEV occurs near apoapsis of the parking orbit. Atmosphere entry occurs 6 to 12 hours later, depending on the parking orbit period, and atmosphere braking begins. The MEV maneuvers towards the landing site and acquires one of the landing beacons delivered with the surface cargo mission. At about 10 km altitude, landing engines are started and the aerobrake is jettisoned. Terminal maneuvering to the landing site is done on rocket propulsion. The final approach is on a 15û descent "glide" slope so that the landing site is visible to the crew on approach. Touchdown occurs within one km of the base.
During the descent, the crew occupies the crew module of the ascent stage to enable abort. Abort is possible during the terminal phase of the aero descent or after descent engines start; the ascent stage can start engines, separate and return to Mars orbit.
After landing the crew performs an ascent stage checkout, powers down and secures the MEV and initiates the surface mission. The MEV health management system remains active during the surface stay to alert the crew of any problem that might call for an abort to Mars orbit.
Upon completion of the surface mission, the crew returns to the MEV, boards the ascent stage, and prepares for ascent. Ascent windows occur at least twice per Mars day, whenever the surface base is in the parking orbit plane. At the first opportunity, ascent is initiated. The MEV ascent stage flies to a 100 km. circular phasing orbit coplanar with the parking orbit. Upon arrival at periapsis, burn to a transfer ellipse (apoapsis coincident with the parking orbit) occurs. At apoapsis the final phasing burn occurs followed by rendezvous and docking with the interplanetary vehicle. The crew transfers and the MEV ascent stage is jettisoned. This nominal ascent occurs about 10 days before the return-to-Earth window closes to allow contingency time.
Trans-Earth injection occurs on a single burn. The coast to Earth is similar to the coast to Mars, with multiple midcourse corrections. Terminal navigation for Earth return is provided by the Deep Space Network (DSN).
About 16 hours before Earth arrival, the crew enters the CRV with the Earth return science. At entry minus 12 hours the CRV separates from the rest of the vehicle. Since the interplanetary vehicle is not on an Earth atmosphere intercept path, the CRV makes a burn of about 20 m/sec to place it on its entry path. The interplanetary vehicle passes by Earth and is abandoned. Earth gravity assist and final attitude control propulsion maneuvers place the vehicle on a trajectory which avoids a later Earth impact. The CRV enters Earth's atmosphere, decelerates, deploys parachutes, and makes a water landing to complete the mission.
Figure 3.4-10 gives a schematic representation of the piloted mission profile (as well as the cargo mission profile).
The ETO scenario for the Mars cargo missions includes the manifesting of the four major vehicle elements along with any secondary elements onto one 250 metric tonne class ETO vehicle with a shroud size of 14 m diameter by 30 m length. In order for the vehicle to fit within this shroud size, the aerobrake is a deployable type and the truss strongback is designed to be collapsable for greater packing efficiency. Once the vehicle has reached its final orbit of 220 n.m., the truss strongback is extended and autonomously berthed with the cargo MEV (which has deployed its aerobrake). The cargo MTV then performs a TMI maneuver which sends the MTV towards Mars on a low-energy, conjunction-class outbound trajectory. Once in the vicinity of Mars, the MTV performs a capture maneuver in Mars orbit. When orbit phasing allows descent to the selected landing site, the MEV de-orbits, jettisons its low L/D aerobrake at about 10 km altitude and lands on the Martian surface. Once on the surface, the landed cargo is translated to within 1.0 m of the surface where it is transferred to a planetary surface system transporter for final relocation and positioning. The cargo lander telemeters its status to Earth to verify a successful touchdown and safes itself until further required.
The core is based on the STS external tank (i.e., 27.6 ft diameter) which is stretched five-feet (i.e., current National Launch System program reference) and enhanced structurally to support a 250 mt payload with a 50 ft x 100 ft shroud (i.e., Mars class). The ogival LOX tank of the ET has been replaced with a standard dome/cylindrical section. The propulsion module is comprised of four STME engines mounted in-line with the propellant tanks (i.e., NLS reference). A 27.6 ft x 60 ft (cylindrical section) payload shroud is used to protect the lunar payloads during ascent.
Each 33 ft diameter booster contains a propulsion module comprised of three F-1A engines. Primary core/booster attachment is accomplished via a thrust beam between the forward adapter of the booster and the core intertank.
The tables in Figure 3.5-2 provide detailed specifications for the lunar and Mars vehicles.
The net payload delivered to orbit is then 154 mt (340 klb) for the lunar missions and 233 mt (513 klb) for the Mars missions. Max g and q requirements were met in both cases. In addition, this assumes an engine-out on the core at liftoff and no booster engine-out.
To support the lunar missions, the following facilities are needed: A new booster processing facility would be required since the NLS core facility cannot support a LOX/RP booster. In addition, this new booster processing facility could be used for core processing. Lunar payloads will require a new processing facility, but the NLS encapsulation facility could support these requirements. Also, the kickstage could be supported in the NLS Cargo Transfer Vehicle/Kickstage (CTV/KS) processing facility. A new Advanced Solid Rocket Motor (ASRM) stacking facility would offload the Vertical Assembly Building (VAB), and VAB high bay 4 could be modified to accommodate this vehicle. A new Mobile Launch Transporter (MLT) would then transport the assembled vehicle to the launch pad. The existing STS launch complex (i.e., 39 A/B) might accommodate a lunar class vehicle, but more analysis would be required. Finally, for both lunar and Mars systems, a new operations support facility would be necessary.
To support the Mars missions, the following facilities are needed: The same core/booster processing facility used for lunar systems would be used for the Mars system. The lunar payload processing facility may accommodate Mars payloads (with modifications), but more analysis would be required. However, a new payload encapsulation facility would be required (size constraint). The NLS CTV/KS processing facility can also support this option. Because of the launch vehicle's size, a new Vertical Integration Facility (VIF) would be required for assembly. A new Mobile Launch Transporter (MLT) would then transport the assembled vehicle to the launch pad. A new launch complex would also be required.
Mars mission requirements between 2012 and 2016 utilize seven 250 mt ETO launches to support the cargo flights; eight 250 mt ETO launches are required for the piloted flights. Multiple launches during one year will be made at 90 day intervals; see Figure 3.5-5.
Current manned-mission operations involving telecommunications, navigation, and information system functions are highly operator-intensive. The complexity of lunar and Mars local mission operations, if forced to operate using current attended monitor and control techniques, will be nearly intractable, risky, and probably unaffordable. In-situ decision making must be provided and links provided among in-situ data systems to distribute information rapidly among elements and allow nearly autonomous operations.
The mission and science elements of the SEI will have compatible communications equipment to ensure that each element can interface with the others. The Synthesis Group Report specifies using the DSN for SEI earth support. The report does not specify any lunar/Mars polar or lunar farside activities; therefore, it is concluded that no lunar relay satellites or martian polar relay satellites are necessary. Figure 3.6-2 provides an overview of the communications infrastructure.
Communications service between the Earth surface and geosynchronous orbit will be provided by the ATDRSS. Current plans call for the ATDRSS to consist of four operational relay satellites and two independent ground terminals. The ATDRSS will be a shared resource with many programs using its capabilities.
An upgraded DSN will support lunar and Mars missions beyond Earth orbit. For support of the precursor missions, one 34 m antenna is required to be added at each DSN complex. For the lunar manned missions, two 34 m and two 4 m antennae are required to be added at each of the three DSN complexes. For the Mars manned missions, four 34 m antennae are required to be added to each complex.
The communications equipment at both outposts will support communications to the Earth and to the surface elements within RF line-of-sight of the outpost communications center. Because no lunar relay satellites are employed, only lunar nearside operations will be supported.
Relay satellites will be needed in Mars orbit to achieve Mars/Earth connectivity of greater than 50%. The first relay satellites will be included with the site reconnaissance orbiter launches in 1998, as called out in the Synthesis Group Report. Due to lifetime constraint, these satellites will only support the precursor missions. The Mars relay network for the manned phases will consist of two satellites in areostationary orbits. The relay satellites will provide dual coverage for activities in the vicinity (²100 km) of the outpost. Nominally, all intra-Mars communications farther than RF line-of-sight from the outpost are accomplished via relay through one of these satellites. These relay satellites will enable greater than 90% connectivity from Mars habitat and mission in-situ vehicles to Earth and to other in-situ mission terminals.
Information Systems
The information system is represented in Figure 3.6-3 in terms of nodes, interfaces, and data flows. Each of the nodes illustrated will contain a portion of the distributed information system. Some nodes, such as those on the vehicles, at the outposts, and those at ground control, will provide centralized support to their area with powerful computer systems to provide the IS services, while other nodes, such as the relay satellites, will contain embedded IS functions appropriate for their own needs. The centralized ground IS communications support systems will provide telemetry data processing necessary for transmission and delivery.
Earth-based systems will plan and schedule the tracking and data acquisition networks. Space-based control systems will monitor and control local nodes based on the network schedule requirements. A centralized control system will be located on the Earth to monitor the network and provide backup control. This centralized information systems control may be co-located and closely integrated with the telecommunications network control.
Initially, the information systems operations will be operator attended. An unattended operations testbed will be deployed on the Moon and will be used for automated operations demonstrations. As unattended operations techniques mature, they will be incorporated into the infrastructure to support Mars operations. The systems will progress from Earth-based operations to largely autonomous. Pre-mission planning support will be provided to the program in order to determine the availability of appropriate communications and information services.
Mars mission elements will require more capable on board systems than the lunar mission elements due to the long communication time delays to Mars. Depending on element requirements, the Mars elements could require very sophisticated management, control, storage, and navigation capabilities that may not be required for the lunar elements.
Navigation
There are three segments of the navigation system: (1) an Earth-based segment, (2) an onboard vehicle segment, and (3) a Mars-based segment. The Earth-based segment constitutes those existing space tracking infrastructures which possess capabilities to support one or more mission phases. The vehicle segment will need to be customized for each vehicle type. All flight vehicles will, however, possess an onboard, autonomous attitude determination and control system and piloted vehicles will possess the requisite level of redundancy and failure tolerance to ensure crew safety. The Mars segment is required for time-critical flight operations near Mars as the comparatively long communication time delay between Earth and Mars precludes dependence upon the Earth-based segment. The Mars-based segment supports independent crew operation for critical phases of operation near the planet by enabling precise, real-time position determination onboard the flight vehicle.
The Apollo program demonstrated that lunar missions require only the Earth-based and onboard vehicle segments. However, the Mars dress rehearsal at Lunar NOC-2 should simulate, to the extent possible, the operations of the Mars segment.
The navigation suite for flight and surface vehicles and the Mars-based segment will be defined from the candidates shown in Figure 3.6-4. The flight vehicles process the onboard navigation data with a space-qualified navigation computer and timing information is provided with a precise onboard clock.
For piloted vehicles, the segments and individual components within the segments will be operated with primary and monitor/backup configurations. For mission critical flight phases, the components will be additionally configured such that the navigation system will continue operation (possibly with degraded accuracy) after the first failure and enter a safe and repairable state after the second failure. For piloted Mars missions, the onboard navigation suite contains navigation aiding devices which make use of the Mars-based segment to perform the primary navigation for time- and safety-critical operations such as Mars descent and landing.
The ATDRSS and DSN will support all pre-launch service planning and testing. Pre-mission support will include determination of interface requirements, applicable network procedures, and development of test plans. Prior to launch, trajectory determination and analysis will be performed for all phases and contingencies of the mission. Data obtained from precursor missions will be used to develop more accurate models and algorithms for spacecraft orbit determination, and surface position for both the manned lunar and Mars missions.
Communications to ground and information systems functions for vehicles during launch, in LEO, and landing will be provided by the ATDRSS system. The ATDRSS and the GPS will support navigation of flight elements. The Earth-based navigation infrastructure will provide the primary navigation for LEO operations. Navigation operations for staging support will include tracking and orbit determination for all elements.
All spacecraft in transit to or from planetary orbit will maintain a direct link to the Earth when line-of-sight to the Earth is achievable. For the information systems, lunar transportation vehicle operations will have Earth-based control systems with on-board systems as backup. The Earth-based navigation infrastructure will provide the primary navigation for trans-lunar injection, trans-Mars injection, and inter-planetary cruise. The Mars transportation vehicle operations will need to be controlled on board due to the long time delays (up to 40 min.) to Earth.
All vehicles in lunar orbit will have a link to the Earth when within line-of-sight on the nearside of the Moon. All vehicles in Mars orbit will have links to the outpost or to the Earth support network via the relay satellites when line-of-sight permits. The link to the surface will only be possible after the surface communications system is emplaced. A communications link between co-orbiting vehicles will be established prior to rendezvous and docking.
For links between elements on the surface, a local communications system is employed which supports a TBD range (outpost zone). Fixed users and mobile users within the outpost zone will communicate with Earth through the outpost communication systems. Nearside lunar users beyond the outpost zone will communicate directly to the Earth support network. Mars elements beyond the outpost but within range of a relay satellite (relay zone) will use the satellite to maintain communications to the Earth and/or the outpost. Mars elements beyond the relay zone will communicate directly to the Earth.
It is the responsibility of LMEPO to evaluate the merits of each of these issues, to integrate similar issues in different functional areas, to prioritize the set of issues, and to recommend requisite studies and trades. The results of this LMEPO integration activity will be published in the document Architecture Analysis Summary and Recommendations, which will be completed soon after the analysis of the four Synthesis Group architectures has been concluded.
The presence of an issue, alternative, or concern in the below materials does not reflect an acceptance by LMEPO, either explicitly or implicitly, of the validity or significance of the issue. Nor does publication in this section imply LMEPO concurrence or support for the funding of studies related to that issue. Synthesized recommendations will be presented in the Architecture Analysis Summary and Recommendations document.
The format for each of the below issues is comprised of an issue number, a concise statement of the issue, alternative approaches, and recommended focused studies. The issue number is ordered, unless otherwise specified, starting from the highest priority and progressing to the lowest according to the contributor's perspective. No attempt has been made to prioritize issues amongst contributors in each functional area. The issue discussion provides a succinct description of the specific strategy or implementation under scrutiny and the particular issue at hand. Issues pertain to the strategy and implementation of the Synthesis Group architecture reference description, not to the theme. The alternative approaches contain options to the Synthesis Group architecture. Each option states how the alternative strategy or implementation deviates from the Synthesis Group Report. In addition, any implications that may occur to the mission or other systems are identified. Finally, the recommended focused studies are discussed as a way to solve an issue or decide on a particular approach. Note that not all issues require future studies. To understand the recommendation, a short description of the focus or purpose of the study and the expected set of analyses are also included.
The identified issues fall into the following functional areas: mission; technology/advanced development; human support; precursor/robotic missions; science; planetary surface systems; space transportation systems; nodes; Earth-to-orbit transportation systems; telecommunications, information systems, and navigation; and operations.
Issue Number: 1
Issue: Unrealistic Schedule
Given the proposed mission scope, the proposed schedule is incompatible with the funding level which Congress and the American taxpayers would currently support. This leads to an unrealistic assessment of the technologies which should be used and to overall unrealistic planning and trade studies for SEI.
Alternative Approaches:
For a given scope, the funding level should be the parameter which is used to determine schedule. This requires a no-buy-in philosophy for estimating cost. Given a budget profile, realistic cost estimates, and a prioritization of activities required to accomplish the mission, schedule can be realistically determined. The budget profile can be the primary assumed parameter and varied parametrically to obtain cost and schedule for each budget profile. Given no management interference, realistic cost and schedule estimates can be provided with existing technology. The result would be a parametric set of schedules directly relatable to the budget assumptions. This approach is compatible with the recommendation of the Augustine Committee and is a realistic approach for obtaining Congressional support for SEI. Congress is very concerned about how much they provide each year for a project, but less concerned with when it is accomplished or how much the project costs over a long period of time.
Recommended Focused Study: Mission Implementation Schedule
It is recommended that the estimating tools to accomplish this task be assembled into a software application and then be applied to generate the parametric schedule estimates associated with a parametric set of funding profile assumptions. It is recommended that a detailed study be made of science requirements, technology status, hardware development schedules, etc. The proposed study would input to the Integrated Plan development and support a program schedule that would account for realistic variable funding levels.
Issue Number: 2
Issue: Commonality of Lunar/Mars Hardware and Systems.
The Synthesis Group Report proposes to use the moon as a testbed for Mars hardware. Although the Report uses caveats like "to the extent practical", it is clear from comments like "... test and operate the actual equipment and systems to be used for the Mars mission." and "The habitat is the same design as the one tested on the lunar surface." that the Report intended significant commonality of hardware between the moon and Mars. It is clear from the physics of the two bodies that little actual hardware commonality beyond the part level can be achieved. Starting with the decent vehicles, Apollo and Viking data support the fact that the two vehicles will be different. Lubrication, material handling, and thermal control are just a few areas where different physical characteristics of the two bodies will require different solutions to similar problems. It is obvious that as much commonality as possible should be obtained; however, the forcing of commonality often results in decreased margins of safety, increased cost, decreased performance, and longer schedules.
Alternative Approaches:
Commonality may exist at the subsystem level or even lower at the part level, depending on the technical feasibility. This applies to both the transportation systems and the surface systems.
Recommended Focused Studies: Lunar/Mars Hardware Commonality
A study is required to evaluate this issue to insure that as much commonality as practical is achieved without undue constraints on the mission hardware. This study should be supported by personnel having hardware design experience for the planetary bodies.
Issue Number: 3
Issue: Artificial Gravity System
The Synthesis Group Report recommended artificial gravity "not to be incorporated". The issue addressed here is not that artificial gravity is needed, but that it is not known that gravity counter measures will be effective. The Report implies that experience in lunar orbit may indicate a need for artificial gravity systems.
Alternative Approaches:
It appears that the data to determine the effectiveness of countermeasures will not be available until after 2000. If the technology for artificial gravity systems is not developed significant program risk is incurred. An alternate approach would be to maintain a low level effort developing the technology for artificial gravity systems in such a way that it could be rapidly accelerated to support program requirements. A segment of the technology effort would be to evaluate emerging space transportation designs for adaptability to artificial gravity systems.
Recommended Focused Studies: Artificial Gravity System
It is recommended that risk assessment be made to determine the effect of programmatic decisions at this time. Analysis should address: technology development requirements, hardware impacts, counter measures data availability, and program schedules.
The following Mission issues were provided by Lewis Research Center.
Issue Number: 1
Issue: Parking Orbit Selection
The selection of an optimum Mars parking orbit is crucial to minimize rendezvous/landing requirements, reduce launch/arrival geometry penalties, maintain abort options and preserve launch window opportunities. The optimum parking orbit strategy is highly dependent on the propulsion system and impacts the burn time requirements.
Alternative Approaches:
The architecture documents currently specify a 500 km circular orbit at Mars. Many different types of parking orbits must be studied to determine the optimum parking orbit strategy for the architecture. The relative figures of merit must be identified to evaluate potential strategies.
Recommended Focused Studies: Parking Orbit Trades Study
Analyses includes the following topics:
Issue: Abort Scenarios
The architectures specify a particular powered abort for each piloted mission. Powered abort scenarios vary substantially between the different propulsion systems, due in part to the difference in failure modes of NEP, SEP, and NTP.
Alternative Approaches:
Other abort options/modes exist and must be studied. These abort scenarios, both powered and unpowered, are primarily dependent on the propulsion system, vehicle configuration, and mission design. The impacts of various abort scenarios on mission and vehicle design must be analyzed. Are the specified abort scenarios feasible/practical? Do abort options exist for the entire mission?
Recommended Focused Studies: Alternative Abort Scenarios
Issue: Ineffective Crew Radiation Protection
Thin skinned crew compartments are the standard for transfer to Mars. No protection is offered against cosmic rays. Quicker trips at great expense are presumed, without clear trade-offs, to be the only available partial solution to cosmic rays. Storm shelter concepts for solar flare protection are so cramped as to be coffin-like, and at that offer minimum acceptable protection.
Alternative Approaches:
There will be a lot of mass on journeys to Mars. Much of this is propellant which can be geometrically reconfigured to protect the crew, even from penetrating cosmic rays. The hydrogen for chemical or thermal nuclear rockets is a potentially great shield. But if it surrounds the crew there are thermal problems, and in nuclear rockets it is needed to shield the reactor. One possible solution is the selection of alternate propellants, to allow thermal compatibility and geometric flexibility. If radiation safety is the prime criteria rather than trip time, these systems may be less massive than the higher performance propellants.
In-situ resources may also change the shielding trades quite favorably. As a combined example, Mars capture or Earth capture propellants of water are excellent shields, excellent nuclear thermal propellants and, if need be, can serve as emergency life support until rescue comes.
Recommended Focused Studies: Reduction of Radiation Exposure through Mission and Vehicle Design
A wide variety of protective spacecraft geometries should be considered, in combination with extraterrestrial resources. Total radiation protection and overall safety should be the major evaluation criteria. The mass cost of quicker trips can be traded against slower, more shielded trips, both with and without space-based materials.
Issue Number: 1
Issue: Use of Chemical Propulsion for the Lunar Transfer Vehicle.
The Synthesis Group Report states that chemical propulsion will be used for the lunar transfer vehicle and nuclear thermal propulsion for the Mars transfer vehicle. The text also specifies technical strategies that call for the use of the Moon as a testbed for Mars, the use of common systems and operations between the Moon and Mars, and the development of nuclear technologies.
Alternative Approaches:
Use the Moon as a testbed for the Mars transfer vehicle by using a nuclear transfer stage for the lunar transfer vehicle. This approach allows testing in a near-Earth environment and commonality between lunar and martian systems.
Recommended Focused Studies:
Assess the application of nuclear thermal propulsion for the lunar transfer stage for initial or follow-on capability.
Issue Number: 2
Issue: Radiation Effects on Crew and Materials.
Travel outside the Earth's magnetic field increases the crew and spacecraft exposure to radiation from the Sun and intergalactic space. The radiation effects on the crew and the systems needs to be assessed for the long duration missions. While there has been attention to the effects on the crew, there has not been sufficient emphasis on the effects of radiation on the potential spacecraft materials and systems. Electronics especially will be affected by the ionizing radiation. Furthermore, as the future size of electronics is reduced the radiation effects become more pronounced.
Alternative Approaches:
There is no real alternative approach if the crew will leave the magnetic shield of the Earth.
Recommended Focused Studies:
Characterize the radiation environment outside the Earth's magnetic field and determine its effects on the crew and materials. The study should address the types of radiation and their intensity as a function of time and direction. Determine the radiation interaction with the crew and materials that may be used in the vehicles and suggest mitigation techniques to reduce radiation effects.
The following Technology issues were provided by Langley Research Center.
Issue Number: 1
Issue: Development of New Technology
Architecture implementation does not promote the development of new technologies and is, therefore, inconsistent with the guiding visions. The Synthesis Group Report recommends the use of limited on-orbit assembly, NERVA, and Apollo-era technologies, as well as compressed schedules.
Alternative Approach:
Limiting on-orbit assembly and using 20 year old technology is not necessarily safer, cheaper, better, or faster. Compressing schedules will no doubt preclude the use of currently emerging technologies. If a vision of SEI is to develop technology, then why reinvent technology that appeared to have little interest in the early 1970's and rush to hardware development without allowing time for the maturation of technologies that could improve safety, reduce costs, improve or performance.
Recommended Focused Studies: Impact of New Technology on SEI Implementation
A study is suggested to evaluate mission requirements, technology maturation, and terrestrial application. This study could be led by Nasa Headquarters Code RS using the Exploration Technology Coordinating Committee (ETCC) with existing data available for technology development. The technology data should be integrated with realistic program schedules, funding availability, and risk assessments.
The following Technology issue was provided by Lewis Research Center.
Issue Number: 1
Issue: NTP Availability and SEI Schedule Compatibility
Significant resources (approx. $13-15 billion) are estimated to be required for developing an expendable, "Apollo-style," space transportation system (STS) for an early return to the Moon (2004-2005). The expendable lunar STS has limited capability and application to Mars systems; therefore, are the development costs for an "Apollo-style" lunar STS a wise investment of scarce SEI resources?
Alternative Approaches:
The Nuclear Propulsion Office (NPO) projected schedule for NTP development calls for achieving a technology readiness level (TRL) of 6 (prelude to flight experiment) of a "near prototypical" flight engine in the 2005-2006 timeframe, with actual flight experiments being initiated in the 2007-2008 timeframe in order to satisfy the "lunar dress rehearsal" missions. By refocusing the approximately $15 billion to develop an "Apollo-style" lunar STS toward development of NTP technology, the schedule can be shortened and a single NTP-based STS applicable both toward the Moon and Mars can be available in the 2005 to 2006 timeframe. Development of a single "modular" NTP-based STS for both the Moon and Mars should reduce the cost of SEI (fewer technology development efforts required) and can begin before final mission dates and requirements are chosen.
Recommended Focused Studies: Application of Nuclear Thermal Propulsion within SEI
Examine the impact of redirecting lunar STS resources ($) toward developing a series of NTP concepts (e.g., Nerva-Derivative, PBR, etc) each having more advanced fuel/engine technology. Determine the NTP performance levels (along with the associated development schedule,risks, and costs) where attractive mission performance is achieved. Emphasis will be on determining the minimum amount of new technology and systems required, the shortest development schedule, and acceptable performance levels for a single NTP-based lunar/Mars STS.
Issue Number: 1
Issue: Artificial Gravity
The Synthesis Group Report dismisses artificial gravity as an option for long duration missions. There is no evidence that "zero gravity" countermeasures will be effective for extended exploration missions. In addition, crewmembers may require a rehabilitation period on Mars, seriously reducing productivity of an initial 30-50 day mission. Further, zero gravity countermeasures, in their present state, pose a significant overhead to the crew in terms of daily productivity and psychological health. Finally, it is not known at all if martian gravity will help with maintaining the physiological health of the crewmembers.
Alternative Approaches:
Artificial gravity should be considered as a countermeasure. It may only need to be applied in a limited amount and/or duration. At worst it may only be complementary to zero gravity countermeasures.
Recommended Focused Studies:
Research to better understand the amount and duration of gravitational force required for adequate physiological health should begin now. Research and development of artificial-gravity, generation systems should begin now.
Issue Number: 2a
Issue: Life Sciences Data/Mars Mission Rehearsal on the Moon
The Synthesis Group Report puts great emphasis on lunar simulations in orbit and on the surface to obtain life sciences data and extrapolate shorter missions to longer ones. While knowledge of human physiological and psychological effects will be gained, it is too late within the architecture schedule for any effective life sciences research and countermeasure development. The dress rehearsal will, however, provide evaluation/validation of system designs and operations without Earth control and logistics.
Alternative Approaches:
Life sciences should be perceived as an enabling function for long-term human spaceflight. A focused program should begin now with ground-based studies and long-duration Shuttle flights. Space Station Freedom (SSF) should be used for life sciences research and countermeasures development. This is necessary to support the C/D phase of Mars vehicles and habitats.
Recommended Focused Studies:
Issue Number: 2b
Issue: Weighted Suit
The weighted space suit concept for a Mars simulation is unproven and, at best, could provide only a few hours per day of simulation. However, this could allow refinement of gravity response curves for different operational tasks. This concept should be assessed to see what would be required to assure fidelity and operational feasibility, including the proper distribution of mass and center of gravity location.
Alternative Approaches: TBD
Recommended Focused Studies: None identified.
Issue Number: 3a
Issue: Closure of Life Support System Loops
Closure is not all-or-nothing but is a matter of degree. It is too early to decide what degree of closure is viable for all mission phases of the architectures.
Alternative Approaches:
Continue development of loop closure technologies for potential use on flights to Mars and for extended human presence on the Moon and Mars.
Recommended Focused Studies: None identified.
Issue Number: 3b
Issue: Food Systems
Although the report does mention that food systems are open for missions to Mars, the technology needs to meet this requirement are not addressed. Food systems must contain food products which are highly palatable. Shelf life requirements for these products must support Mars missions.
The Synthesis Group Report talks about possibly closing the food loop by recycling both human and plant wastes yet there has been little work on producing engineered foods from basic macronutrients. The palatability of these food items is in question, as well as the fact that engineered foods may not provide adequate nutrition. There was also no mention of food biotechnology in providing in-situ food products.
Alternative Approaches:
Food packaging, preparation, and in-situ processing should be addressed. In particular, in situ technology could provide high quality and palatable food products for long duration missions.
Recommended Focused Studies:
Establish a food systems development program.
Issue Number: 3c
Issue: Waste Management Technologies
While the waste management technology for human wastes and packaging materials is addressed, there is no mention of the technology needs for handling additional types of trash or waste products, including collection, handling, treatment, stabilization, storage, processing, recycling and disposal of trash/waste products.
Alternative Approaches: TBD
Recommended Focused Studies:
Support development of all areas of waste management.
Issue Number: 4a
Issue: Single Suit (space and planetary surfaces).
There is some concern that a single space suit is not the best option to allow maximum safety and productivity in all environments.
Alternative Approaches:
Use the existing Space Shuttle suit for contingency use during spaceflight. Develop a modular suit concept with variable pressure which can be used in both lunar and martian environments.
Recommended Focused Studies: None identified.
Issue Number: 4b
Issue: Habitat Internal Atmospheric Pressure and Composition.
Although some of the advantages of a 5 psi, 70 percent oxygen atmosphere were described, no mention was made of disadvantages. These disadvantages must be addressed.
Alternative Approaches: None.
Recommended Focused Studies:
There is enough data to make a decision for both pressure and composition for a safe, operationally effective atmosphere. This decision should be made early since it affects materials selection, system designs , operational procedures, etc.
Issue Number: 5
Issue: Rover Excursion Ranges
A large excursion range precludes EVA walk-back. In addition, a crew rescue capability during all mission phases was not included as a part of the mission abort principles.
Alternative Approaches:
It is not reasonable to limit all excursion ranges to an EVA walk-back range. Therefore, extended ranges may require that the rover have an adequate repair capability in the field, and safe haven life support provisions. A second rover could be used for contingency crew rescue. While a second rover may be used for most contingency rescue scenarios, it would not be used to rescue a crew during a solar flare event. Protection from solar flares may necessitate a storm shelter provision designed into the rover or the capability to rapidly construct a shelter.
Recommended Focused Studies:
A risk assessment must be made to allow a programmatic decision on the degree of crew rescue capability necessary for the program.
Issue Number: 6a
Issue: Telerobotics/Telepresence Versus Supervised, Intelligent Autonomous Systems
Although telerobotics is now the state of the art, intelligent robotics can provide a much higher leverage. Operations, systems, science, etc., tasks should be examined for human intervention and control versus intelligent systems which require minimal supervision. Extensive use of intelligent systems for monitoring, control and failure management and the use of supervised autonomous robots may be required to assure the productivity of the crew for science and surface operations. A judicious mix of telerobotics and automation and robotics can dramatically increase productivity, minimizing logistics, while reducing risks and improving safety and reliability.
Alternative Approaches: TBD
Recommended Focused Studies: None identified.
Issue Number: 6b
Issue: Outpost Maintenance During Human Absence.
Outpost maintenance during human absence was not defined in the Synthesis Group Report as a functional capability. A strong degree of confidence must exist that a habitat is still safe and viable before a commitment is made to return a crew.
In addition, separate delivery of habitats, vehicles, etc. will require the development of sophisticated on-orbit and surface robotics and automated checkout systems for deployment, emplacement and verification of operability without the presence of humans.
Alternative Approaches:
The goal of a supervised autonomous outpost should perhaps be adopted.
Recommended Focused Studies: None identified.
Issue Number: 7a
Issue: Characterization of Environment
The report does not adequately address the entire space environment. A complete characterization must include radiation, life support, noise/vibration, microbiology, toxicology, human factors, etc. Understanding must also involve environment interactions and total environmental impact for both space and planetary environments.
Very little mention was made of problems incurred with the control of lunar and martian dust over long periods of time. Dust presents both maintenance and contamination issues.
Alternative Approaches: TBD
Recommended Focused Studies: None identified.
Issue Number: 8
Issue: Human Support Integration
Although the report addresses many of the human support issues and concerns, it makes no mention of how human support as a whole is integrated into the architecture strategy.
Alternative Approaches:
Integrate human support operations and research personnel with engineers early in the design phase of all vehicles and habitats so medical, environmental and human factors issues can be integrated early.
Recommended Focused Studies: None identified.
Issue Number: 9
Issue: Analog Comparisons
The Synthesis Group Report did not adequately address the use of analogs.
Alternative Approaches:
Terrestrial analogs need to be assessed for their contributions to operational, psychological and psychosocial knowledge. Variables which affect operations or crew performance in isolated and confined environments need to be identified. Controlled experiments could then be carried out to determine appropriate countermeasures to these variables.
Recommended Focused Studies: None identified.
Issue Number: 1
Issue: Mismatch of Themes, Implementations, Strategies, and Architecture Objectives:
For the Mars Exploration Architecture, the Synthesis Group Report states: "The major objective of this architecture is to explore Mars and provide scientific return" using a cost-minimal approach. The Report also states that "All architectures envision a robust Mars exploration program that consists of complementary robotic and human elements...designed to give first-order answers to some of the most fundamental questions of planetary science." It would seem that visiting two sites on Mars (the minimum number of piloted flights identified for this Architecture) and learning a great deal about these two sites but not learning much at all about the rest of the planet to at least understand the context into which these two sites should be placed (as implied by the lack of additional robotic missions to other locations, the minimum necessary to learn about them as well) is incongruous with this "major objective." The primary objective of the robotic missions included in this architecture is to gather imagery data from 12 candidate sites (for site selection and hazard detection purposes) and to land at two of these sites which will eventually be visited by the human crews. This misses the opportunity to investigate Mars on a global scale and to visit other surface sites - robotically - for a relatively small increase in the marginal cost of the total program. Inclusion of additional orbital and surface missions will improve the understanding of Mars as a planet and in turn could assist in selecting the sites where human crews could be used to the best advantage. In addition, this architectures provides human global access to Mars. A 50-100 km traverse capability by humans in a pressurized rover comes nowhere close to meeting this objective and yet the Synthesis Group Report, p.5, states, "...the permanent presence of humans ... gives us an impressive scientific capability ... [E]xtended traverses in pressurized rovers will permit detailed study of puzzling lunar features and processes." Science rovers which can, over 3 to 5 years, reach diverse regions on planetary bodies could fulfill the promise of the Synthesis Group Report for Mars. In general, robotic precursor mission strategies and implementations are not based on an evaluation of the theme/objectives trade space which could be accomplished with an analysis of the cost-risk-benefit trades.
Alternative Approaches: TBD
Recommended Focused Studies: Robotic Precursor Mission Strategy and Assessment
(1) Prepare a more detailed science strategy that meets the objectives of exploring Mars and providing significant science return followed by an assessment of how a combination of robots and humans can be used effectively in this strategy. (2) Evaluate Robotic Precursor Mission requirements and implementations in the trade space of cost-risk-benefit for an appropriate selection of architecture strategies which address the Synthesis Group Report exploration themes. (3) Assess the impacts of using micro-electronics and micro-mechanical systems as a means of accomplishing a larger number of missions, with greater diversity, for a comparable investment of resources.
Issue Number: 2
Issue: No Robotic Mars Sample Return
a) Crew Safety and Risks To Humans On Earth: It is argued that a sample return (SR) is not needed because toxic hazards can be identified and assessed on the surface and the long trip back to Earth will serve as a quarantine period to detect any Mars bugs infecting the crew. Synthesis Group policy on SR may be inconsistent with their risk priority policy, which states that crew safety is first, system infrastructure second, and the Earth biosphere not even on the list. The use of the crew as test subjects for potential Mars biota places the crew in jeopardy, in favor of protecting Earth. If crew safety is indeed the highest priority, then that probably justifies a better strategy for understanding the potential hazards, a sample return being high on the list for accomplishing this. Whatever priority is assigned to protection of the crew, the protection of everyone else should get that same priority. The possibility of back contamination and nuclear accidents must be included into the risk analysis, and in these cases the main threats are to those on the ground.
Toxicity is an issue separate from the biological hazard potential. First, the current protocol for determining if a new or unknown substance is toxic is to expose living creatures to that substance and observe its effect. There are no other means (e.g., computer models) for determining the effects of an unknown substance. Second, a battery of test could be performed to determine if substances known to be toxic are present in the martian environment. However, the equipment needed to carry out these tests is not likely to be easily carried on a surface rover, as proposed by the Synthesis Group, without that vehicle becoming quite sizable. A better strategy for determining an acceptable level of risk to the crew from possible toxic sources is needed, and a sample return is currently the only way of carrying out a comprehensive series of tests.
b) Mars Science Return: The science community has stated their highest Mars priority is to get a sample from each of Mars' eight basic terrain types (Reference: "Strategy for Exploration of the Inner Planets: 1977-1987," COMPLEX, National Academy of Sciences, 1978, updated 1990). The architectures completely defers this requirement until the arrival of human crews and will in fact tend to localize activities around 100-km radius areas of human presence. Only beyond the timeframe addressed by the architectures, when people will have built up their infrastructure enough to have visited all the terrains, will this scientific objective be accomplished. However, a sample return capability by 2003 is within the technological realm of possibility. In addition, terrains hard to reach by the piloted missions, such as polar terrains, may be feasible with robotic missions.
Alternative Approaches:
Include at least one sample return mission from the primary landing site for the first human crew and include this capability on later missions, either in conjunction with or separate from successive human missions, to visit sites not visited by humans but of scientific interest.
Recommended Focused Studies: Planetary Protection and Toxicity Assessments
(1) Support ongoing planetary protection assessments and begin to develop the details of a strategy that will address scientific and legal issues that must be answered prior to the arrival of the first humans. (2) Assess toxicological hazards based on currently available data (i.e. Viking data) and those areas of potential hazard (e.g. chemically reactive dust) for which insufficient data exists; develop a set of tests and the associate payload that will certify a site as reasonably safe for the crew to explore ("reasonably" to be defined in conjunction with LMEPO); identify acceptable means for carrying out these tests (this could involve in situ tests at Mars or may require a sample return to Earth prior to the first crew's departure).
Issue Number: 3
Issue: Lunar Rover Precursor
The groundrules for the Mars Exploration architecture specify that sites on the moon, to be used as Mars analogs, will be selected based on existing data. This is a reasonable approach for selecting a landing site, but the activities to be carried out by the first human crew go far beyond those of an Apollo mission. Large structures and heavy equipment will be used to set up permanent facilities at the selected site. But just as with a terrestrial construction site, a survey team will examine the surface and subsurface in detail to help the architect plan the proper placement of the structure that will occupy the site. With a limitation of 14 days on the surface for the first crew, using part of that time to understand the site in sufficient detail for base layout is improper and can be satisfied by other means, namely an automated or teleoperated rover. This vehicle would be used for site certification, a process not described in detail by the Synthesis Group, not site selection and for base layout planning and cargo mission manifesting (i.e. what heavy equipment must be brought along on the first mission). This strategy is consistent with using moon as precursor to Mars missions. The use of a surface rover is the proposed procedure for Mars (i.e., scout the site with a rover first) and thus a lunar rover mission would serve as the precursor for both vehicle design and for mission operations (i.e., what must you do to certify a site and how do you do it).
Alternative Approaches:
Include at least one lunar rover as a precursor to piloted flights to the moon and as a precursor to similar rovers sent
to Mars. Recommended Focused Studies: Lunar and Mars Rover Commonality Study
This issue was addressed in the JPL response to the NASA 90-Day Study (Reference "A Robotic Exploration Program," JPL D-6688, December 1, 1989) with the result indicating that rover commonality is feasible. The next step in concept development is needed: begin to assess specific system and technologies for the vehicle and payload. This assessment should focus on miniaturization of components and systems to reduce the size and mass of the rover and thus reduce the transportation costs. In addition, the set of tasks to be accomplished by this rover and the payload needed to carry out these tasks must be examined in more detail.
Issue Number: 4
Issue: Telepresence Limitation
Operating a telepresence rover is not viable for robotic missions conducted from Earth; feedback control systems cannot be built that can control this type of system with the inherent time lags involved (i.e., insufficient control system bandwidth). For example, a robotic hand may crush the object it is holding or may damage itself due to the time lag which prevents the operator from realizing that the object may be crushed or the hand damaged before it actually happens. Only on the downlink side (e.g., neat "you are there" 3-D displays of what the surface is like) is there some application. Telepresence probably does not apply to activities conducted from Mars orbit for similar and other reasons. There is not enough time over an individual site to get more done than could be via Earth commanding with reasonable on-board autonomy. Telepresence probably does not apply even to activities conducted from Mars surface for the following reasons: (1) There is not enough control system bandwidth to sites over the horizon if a communications satellite relay is used, and (2) science return could be greater - and sooner - and cheaper - with semi-autonomous missions conducted from Earth with a fraction of the technology risk of telepresence. As stated on page 5 of the Synthesis Group Report: "Robotic assistants will extend human reach for great distances across the lunar surface." However, most of the work time will be spent getting from place to place, a task that can be automated.
Alternative Approaches:
Include a larger number of semi-autonomous and/or teleoperated rovers at the expense of fewer or no telepresence rovers to increase the number of sites visited and data returned for comparable resources.
Recommended Focused Studies: Telepresence Benefit Analysis
A cost-benefit-risk trade study that would address science, technology, and engineering implementation factors and include a control-method trade-off study among IVA for telepresence vs. EVA vs. Earth-based command & control. (Activities within this study will be closely linked to those discussed under issue number 1.)
Issue Number: 5
Issue: Site Reconnaissance/Communications Orbiter Compatibility and Programmatics
The Synthesis Group Report states that "Communications orbiters are needed for data relay on rover and human missions. Combining this capability with that of the site reconnaissance orbiter is preferable...." Two fundamental problems related to compatibility and programmatics result from this statement. First, past studies of the reconnaissance orbiter and communications orbiter indicate that these two functions cannot be combined on a single spacecraft due to differing operational orbit requirements. Second, it is not clear that a communications capability, regardless of the other capabilities it is combined with, placed in Mars orbit during the 1998 opportunity will be functional when the first human crews arrive approximately 16 years later.
Alternative Approaches:
Launch the communications orbiters (COs) separately from and several years later than the site reconnaissance orbiters (SROs). Implications: the SROs will have to return all of their own data but the COs will not have nearly as high a systems lifetime or risk for their other mission of supporting Mars surface activities (e.g., Mars rover and human missions) which start five years after SRO launch; the launch mass for the SRO can be lower resulting in higher launch margin and/or smaller/less costly launch vehicles as a possibility.
Recommended Focused Studies: Site Reconnaissance/Communications Orbiter Analysis
(1) Detailed design study for the SRO including programmatic alternatives for meeting the 1998 launch opportunity and provisions for on-board, high data rate communications with Earth (i.e. no communications orbiter support during the primary mission). (2) Assessment of the communications requirements for support of rovers and human crews including vehicle conceptual designs and mission plans which discuss replenishment of these communications assets during the later phases of this architecture.
The following Robotic Mission issues were provided by Lewis Research Center.
Issue Number: 1
Issue: NEP for Precursor/Robotic Missions
Advanced propulsion systems, particularly nuclear electric propulsion (NEP), were not considered as effective means for the precursor robotic missions scheduled for Mars exploration.
Alternative Approaches:
Nuclear electric propulsion can perform enabling near term precursor/robotic missions, while utilizing or leveraging existing power and thruster technology programs. Mission flexibilities such as extended departure windows are afforded by high specific impulses and extended thrusting times. Precursor/robotic NEP missions can benefit programmatically from existing reactor and thruster technology programs and high commonality with surface power systems.
Recommended Focused Studies: Application of NEP to Robotic Missions
Issue Number: 2
Issue: Solar Electric Propulsion Precursor/Robotic Missions
Advanced propulsion systems, particularly solar electric propulsion (SEP), were not considered as effective means for the precursor robotic missions scheduled for Mars exploration.
Alternative Approaches:
Solar electric propulsion vehicles should be evaluated as an expeditious, efficient means of transporting orbiting satellites to the Moon and Mars and as a cargo vehicle for probes to the surface. Precursor missions using advanced propulsion may be expedited toward an earlier launch should SEP be employed. SEP has flight experience (SERT I and II) while nuclear electric and nuclear thermal do not have any flight experience. The ELITE program under the auspices of the U. S. Air Force is scheduled for the mid-1990's and will give additional experience in solar electric propulsion. Using current state-of-the-art technology, probes could be sent to Mars or the lunar poles. Using advanced SEP technology would reduce flight time and would permit very large payloads, such as landers, rovers, and ascent vehicles.
Recommended Focused Studies: Application of SEP to Robotic Missions
Issue Number: 3
Issue: NTP for Precursor/Robotic Missions
Advanced propulsion systems, particularly nuclear thermal propulsion (NTP), were not considered as effective means for the precursor robotic missions scheduled for Mars exploration.
Alternative Approaches:
Nuclear thermal propulsion should be investigated for application to precursor/robotic missions. Numerous mission flexibilities, such as abort capabilities, increased payload, and extended departure windows are possible with NTP. Figures of merit include mission performance, applicability to other missions through evolution and commonality, cost, availability and readiness.
Recommended Focused Studies: Application of NTP to Robotic Missions
Issue Number: 1
Issue: Level of Detail for Moon and Mars Science.
Common lunar science activities described in the Synthesis Group Report stress high level goals and themes, but not specific capabilities or strategy. This is inconsistent with the Synthesis Group discussion of Mars, which goes into considerable detail regarding access, capability and stay time issues.
Alternative Approaches:
The alternative is to maintain internal consistency when outlining mission goals and themes for both the Moon and Mars.
Recommended Focused Studies: No further study required.
Issue Number: 2
Issue: Misalignment of Science Goals with Mission Capabilities.
The primary theme of the Mars Exploration Architecture is to "explore Mars and provide scientific return..[which also] permits meaningful scientific return from the Moon." However, the architecture description goes on to suggest a minimalistic approach to mission implementation, deploying a limited set of small science instrument packages on the surface with limited time allotted to exploration. This does not enable a "meaningful" science program for the Moon or Mars. For example, in the common discussion of architectures, the report states that the Moon will be used for astronomy, but Architecture #1 never specifies developing any sort of capability with telescopes.
Alternative Approaches:
An alternative is to more closely align the stated mission goals with the mission capabilities and accomplishments.
Recommended Focused Studies: No further study required.
Issue Number: 3
Issue: Orbital Science Opportunities.
Orbital science, or observations and experiments conducted while orbiting the Moon (in the Mars dress rehearsal) or Mars, is described in the report as "desirable", but it is not baselined as a common activity. However, there is time in orbit both during the Mars dress rehearsal and while in the Mars system if there is an abort, to do a certain amount of science. Flights need to be equipped with the appropriate science instruments to take advantage of these opportunities while in orbit. For example, in order to conduct telescience from orbit, advanced planning for that contingency is necessary. Teleoperated rovers need to be emplaced on the surface in advance so that there are rovers to operate from orbit. This becomes both a science issue as well as a manifesting issue, as the rovers and communications infrastructure that could be used to conduct such a science program would need to be deployed prior to the arrival of manned spacecraft.
Alternative Approaches:
One alternative is to deliver surface rovers on cargo flights preceding piloted flights that may entail time in orbit.
Recommended Focused Studies: No further study required.
Issue Number: 4
Issue: Pressurized Rover Operations and Support.
The Synthesis Group Report is very clear that pressurized rovers will be used at some point in all architectures. From a scientific perspective, this is a highly desirable mission element. However, the infrastructure needed to support pressurized rovers is not discussed, nor the issues of resupply, rover design, and extended pressurized rover operations crucial to their use.
Alternative Approaches: None.
Recommended Focused Studies: No further study required.
Issue Number: 5
Issue: Duties of Dress Rehearsal Support Crew.
During the Mars dress rehearsal, it is unclear as to what the full duties and options are for the "clean-up crew" that monitors the simulation and stays behind to monitor instruments. This time could be used fruitfully for additional scientific activities, and should support the ongoing experiments and exploration.
Alternative Approaches: None.
Recommended Focused Studies: No further study required.
Issue Number: 6
Issue: Cruise Science Opportunities.
No mention is made of cruise science including experimental biomedical research, astronomy or space physics which can be done during the Mars transits. While this is minor compared to surface science, it should at least be mentioned.
Alternative Approaches: None.
Recommended Focused Studies: No further study required.
Issue Number : 1
Issue : Validity of Mars Simulation - Location
The Synthesis Group calls for a complete dress rehearsal for the mission to Mars. This is initiated with a cargo flight to the lunar site chosen. This site is "...in close proximity to the original site ..." of emplacement. The access by the support crew and necessary support equipment might be hindered by this separation.
Alternative Approaches :
Locate the Mars simulation adjacent to existing emplacement or an appropriate distance that would be within a realistic operational range of equipment.
Recommended Focused Studies : Mars simulation site location on the Moon.
Issue Number : 2
Issue : Validity of Mars Simulation - Commonality of Elements
The Synthesis Group calls for a complete dress rehearsal for the mission to Mars during lunar NOC 2. This "...simulation mission uses the full suite of equipment to be used for the actual Mars mission as much as practical...". The items and "support services" needed may be similar, but the mass, volume and subsystems required for these elements, such as power and thermal control, will be different because environmental conditions on the Moon and Mars are not similar.
Alternative Approaches :
Reduce Mars simulation to test of human physical capability only, and tests of deployment techniques. Actual Mars hardware might be tested in Earth-based simulations.
Recommended Focused Studies: Commonality of Lunar and Mars Elements
A study should be undertaken to investigate the commonality of actual Mars hardware (and it's deployment) with lunar hardware, such as:
Issue Number : 3
Issue: Validity of Mars Simulation - Full Up Verification Philosophy
The Synthesis Group Report calls for a complete simulation of a Mars mission during lunar NOC 2. The existing unloader and pressurized rover are used, and duplicates of other systems, such as the power supplies and habitats, are delivered to the simulation site. Since these have already been in use for some time, nothing is gained by testing their deployment and operation a second time. Only the advanced life support system in the habitat is being used for the first time.
Alternative Approaches:
Piecewise verification: a series of missions that cumulatively show, verify, and simulate Mars mission capability. This allows for smoother cost profiles, opportunities to learn and improve systems, isolation of problems and difficulties, and reduced risk on each individual mission.
Recommended Focused Studies: Alternatives for integrated Mars simulation
Identify what needs to be verified and simulated for Mars preparation. Develop a network of verification/simulation activities. Allocate activities into various sized mission packages. Evaluate allocation approaches with regards to cost, risk, and ability to impact actual Mars mission and systems.
Issue Number : 4
Issue: Minimum Mission
Many systems are duplicated on the Moon in order to provide a "complete Martian simulation base". This is not a characteristic of a "minimal approach" because 1) of the added cost and 2) equipment that is provided is used only once, for a short period of time, and then abandoned.
Alternative Approaches:
This duplication can be eliminated without sacrificing a physiological crew simulation at a single lunar base. Equipment which is common between the Moon and Mars could be tested, but Mars-unique equipment still may not be tested on the Moon.
Recommended Focused Studies: Design of a minimum Mars Exploration Architecture
Issue Number : 5
Issue: Full Up Robotic Emplacement Installation
The Synthesis Group Report calls for the complete lunar outpost to be delivered and made operational before the crew arrives. This requires larger overhead for construction machinery, more risk in remote operations, high initial cargo rates to the surface, and longer payback time.
Alternative Approaches:
Initial flights establish significant but limited capability that is added to with succeeding flights. The method of growth is to duplicate the smaller building blocks or use succeedingly larger blocks.
Recommended Focused Studies: Appropriate Level of Automation and Robotics
The study should investigate desirable growth profiles with identification of areas that can have a realistic reliance on automation and robotics based on current technologies. Also should investigate the proper mix of robotic and human activity in surface element emplacement.
Issue Number : 6
Issue: PSS - ST Interface
1) The Synthesis Group Report calls for an unloader to be delivered on the initial cargo flight for lunar IOC. Because the surface payloads are at >5 meters above the surface when delivered on the Space Transportation cargo lander, the unloader manifested by PSS has a mass of 15 mt. Present studies indicate that this mass could be reduced to 5 mt if the payload could be delivered within 1 meter of the surface. 2) Landers on the surface for extended periods require power, thermal control, micrometeoroid protection, etc. It is not clear how much of this should be provided by the lander and how much should be provided by surface equipment.
Alternative Approaches:
1) Simpler means could be employed for offloading such as rails, ramps or cables. However, the payloads would likely have to be lower to the surface. Smaller machinery or attachments could provide required surface preparation, transport, etc. Another alternative is to leave the habitat on the lander.
2) The landers could be completely self sufficient, or they could rely on various levels of surface-supplied services.
Recommended Focused Studies: PSS-ST Interface, Study the possibility of moving the PSS - ST interface to LLO.
Studies should investigate alternate methods of cargo placement on the space transportation vehicles, such as underslung, etc. Also should study methods of maintaining landers on planetary surfaces. Strategically, study is required to minimize the interface issues between ST and PSS.
Issue Number : 7
Issue: Operational Sizing
Systems are optimized toward a particular targeted capability (5 crew for up to 14 days, 6 crew for up to 90 days) and this capability is established from the outset. This has a direct influence on operational complexity required, particularly in the area of maintenance required on these emplaced systems. This creates significant initial investment in systems and delivery that must be paid back with mission benefits over an extended time.
Alternative Approaches:
More gradual, modular build up of surface capabilities. Infrastructure pieces are sized to smaller building blocks (e.g., 2-3 crew for 14 days) that are sequentially added to arrive at end goals. This does not necessarily optimize reaching a single particular operational state but can provide greater flexibility in operations procedures and more immediate payback on infrastructure investments.
Recommended Focused Studies: Operational System Modularity, Maintenance burden studies, Spares analysis.
Study should investigate level of system modularity (elements, subsystems, components, É), and size of basic modular components. Feasibility / costs / benefits of modular system designs should be investigated. Maintenance burden studies should be carried out in parallel.
Issue Number : 8
Issue: Radiation Protection for Crews on the Lunar Surface
During lunar IOC and subsequent NOCs, it is uncertain when radiation protection utilizing regolith is required. The first three piloted missions are 14, 14 and 60 days in duration. There is at present no definitive guideline for the need and amount of radiation protection required. Should the habitation areas already be covered for the initial crews before they arrive? Can it wait until 30-day or longer missions? Regolith shielding thickness is a major driver for surface habitat emplacement strategies.
Alternative Approaches:
No radiation protection (regolith covering) for initial crews staying 14 days, with regolith shielding being provided for the first crew to stay for an extended time (60 days). The other approach would provide regolith shielding material covering habitation areas from the start, including the 14 day missions.
Recommended Focused Studies: Radiation Abatement Guidelines
Effects of solar and galactic radiation on humans in reduced gravity must be studied so that realistic standards for dosage can be developed. Dosage standards can then be used to derive appropriate shield thicknesses.
Issue Number : 9
Issue: PVA/RFC Backup for Nuclear Power
The Synthesis Group Report specifies that PVA/RFC should be used as backup for nuclear power systems on the planet surface. The result is a duplication of power generation capability with two systems being maintained at levels that are never actually used. Indeed, either system alone must provide adequate power for the envisioned level of activities.
Alternative Approaches:
Use one system alone with enough reliability to guarantee minimal power level. If a totally separate back-up system is chosen, scale backup to minimal levels and install primary power system at the outset.
Recommended Focused Studies: Power generation integration and distribution options
Determine optimum power strategies that incorporate the use of integrated primary and backup systems, with the capability to handle possible future expansion of power users.
Issue Number : 10
Issue: Pressurized Rover Delivered on Initial Cargo Flight(s), Mars IOC.
This rover is required to sit on the surface for two years before the first crew arrives to use it. The issue involves the requirement to keep the rover "alive" during this time. Also, technology advances might occur during that time which would improve performance of the rover.
Alternative Approaches:
The crew brings all surface transportation elements with them on the piloted mission, including the pressurized rover.
Recommended Focused Studies: Pressurized rover designs - alternatives
Issue Number : 11
Issue: Consumables for Second Mars Piloted Mission
The consumables and pallet needed for the second piloted mission in 2016 weigh 30 metric tons due to the 600 day stay time. This is more than triple the 9.2 metric ton down-mass capability of the current lander design. A major portion of the consumables is food, which cannot be delivered on the preceding cargo flights due to shelf-life limitations.
Alternative Approaches:
The consumables that are not perishable could be delivered on a cargo flight that precedes the arrival of the crew. This, however would occur 2 years before their arrival. Another alternative is resupply with early return option if contingencies arise.
Recommended Focused Studies:Storage requirements and "shelf life" of consumables needed for Mars missions with extended stay times.
Issue Number : 12
Issue: Lunar and Mars Mission Crew Size
In the Synthesis Group Report, all crews for lunar and Mars missions are sized at six, with five to the surface on the first lunar piloted mission. This results in the need for significant surface capability at the outset which in turn requires significant offloading/construction ability.
Alternative Approaches:
Restrict early crew size so that initial systems can be smaller. Crew size is then increased with subsequent missions, allowing operations and infrastructure to grow in parallel.
Recommended Focused Studies: Operational assessment of minimum crew size
Issue Number : 13
Issue: Orbital vs. Surface Staging of Mars Exploration
Early Mars exploration as presented by the Synthesis Group is staged from the surface. This requires emplacement of significant infrastructure at the outset at one site, even before crew arrives. Even the second mission of 600 day duration is limited to one site and its environs. A true "minimal exploration mission" might limit emplaced infrastructure on the surface and allow for exploration of several areas.
Alternative Approaches:
Low orbital staging - small crew sorties from an orbital facility to areas of interest. With development of ISRU propellants this could become attractive.
Recommended Focused Studies: Feasibility of small encampments utilizing the Mars Excursion Vehicles as the "base camp"
The following Planet Surface issues were provided by Lewis Research Center.
Issue Number: 1
Issue: Surface Transportation Vehicle Operations Effect on Power System Selection.
The definition of a surface transportation vehicle (STV) operational scenario has major impacts on the selection of the power system technology and resultant vehicle configuration. The Synthesis Group Report recommends the use of non-nuclear power sources which in general, require rest periods (recharging) in vehicle operational scenarios. The Synthesis Group report suggests that plutonium availability is such that nuclear STV power sources are undesirable.
Alternative Approaches:
Nuclear power sources offer continuous power availability eliminating the need for rest periods. For this reason, the option of nuclear power may provide enhanced mission opportunities. Radioisotope power systems such as RTGs or DIPS should not be discounted because of perceived plutonium availability. The DOE has established plans for increasing Pu238 production consistent with SEI requirements. Further, international supplies of radioisotope fuel may ameliorate any shortfalls.
Recommended Focused Studies: Surface Transportation Vehicle Power System Options
The impact of required rest periods on STV operations and the effect on the attainment of mission objectives must be studied. In addition, the infrastructure that may be needed to support non-nuclear power sources on STVs should be quantified. On board non-nuclear power generation (i.e. photovoltaic arrays) for continuous recharging of energy storage systems must be assessed as to its impact on vehicle design and operation. The use of nuclear power sources on STVs and the potential enhancement to mission opportunities must be weighed against plutonium availability and the cost of re-establishing production. In addition, the safety concerns associated with nuclear power sources must be addressed and the impact on vehicle design and operation evaluated.
Issue Number: 2
Issue: Testing of Mars Power Systems in the Lunar Surface Dress Rehearsal.
The Synthesis Group Report suggests a strategy for testing Mars elements in a lunar surface dress rehearsal. The objective of this strategy is to provide a representative testbed for systems to ensure their successful implementation for future Mars missions. However, the lunar environment does not provide representative conditions for Mars power systems. The Mars photovoltaic/regenerative fuel cell (PV/RFC) system will be subjected to a vastly different night period from the Moon (12 hours for Mars versus 354 hours for the Moon) resulting in a greatly reduced energy storage requirement. Further, solar insolation at Mars is reduced because of the increased distance from the Sun, CO2 atmosphere, and weather effects resulting in potentially different solar cell technologies and array designs from those employed in the lunar environment. Lunar nuclear systems which employ high temperature refractory materials subject to oxygen contamination must be significantly modified to withstand the Mars CO2 atmosphere. Finally, the effect of Mars ambient temperature and dust storms will result in considerably different design approaches for waste heat radiators.
Alternative Approaches:
The Mars environmental effects on power system design can be much better simulated on Earth. Therefore, Mars power systems should be tested on Earth. The testing objectives should focus on resolving the impacts of the Mars environment on power system design with consideration to the performance and operation of the lunar power systems. The time lag between Mars and lunar missions allows opportunity to take into account experience gained from operation of the lunar power systems. Further, the time between Mars and lunar missions could permit additional technology and system development. The net result will be that the Mars power systems will have superior quality and performance than their lunar counterparts.
Recommended Focused Studies:
None identified at this time.
Issue Number: 3
Issue: Surface Nuclear Power System Use and Implementation.
The present design strategy for surface nuclear power plants requires additional examination. In particular, there are several critical issues which should be addressed prior to selection of a baseline nuclear power plant design option. Reactor radiation shielding can be accomplished by either enclosing the reactor in a 4¹ shield or placing the reactor in a surface excavation. The Earth-delivered enclosure shield results in a considerable mass penalty but minimizes the amount of on-site construction. System installation can be accomplished by a number of ways including autonomous deployment, crew EVA, telerobotic assembly or any combination of the three. Self-deployable systems pay a slight mass, volume, and complexity penalty but can be installed without consideration of crew or construction equipment availability. The Mars nuclear power system design must take into account the CO2 atmosphere effects on high temperature refractory materials. A variety of options exist to counteract the Mars environment but all will impact the power system mass, volume, lifetime, and operations. Finally, the selection of the power conversion method will have considerable impact on system performance, operations, and technology development risk.
Alternative Approaches:
Consideration must be given to the above issues prior to selection of a baseline surface nuclear power system design strategy. The selection of the design option should be consistent with the specific architecture requirements.
Recommended Focused Studies: Analyses for Selection of Surface Nuclear Power System
Studies should be performed to examine the various approaches for reactor shielding, system installation, Mars environment material protection, and power conversion selection as they apply to the specific architecture power requirements.
Issue Number: 4
Issue: Dust Effects on Lunar Power Systems.
Lunar dust is omnipresent, easily lofted, and clings tenaciously to virtually every surface in the hard vacuum environment. An effective lunar dust removal procedure does not exist today. Lunar dust can dramatically degrade the performance of solar cells, radiative surfaces, and optical systems. Hardware may become permanently dust coated during initial deployment, and could become more so if vehicles or human activity is present in the vicinity.
Alternative Approaches:
Dust avoidance and dust removal are the only alternatives for lunar surface operations. Strategies and technology for dust avoidance or dust removal need to be developed and proven. Design margin must be allowed for system degradation due to clinging dust.
Recommended Focused Studies: Solutions to Lunar Dust
Define a research program of dust avoidance and dust removal techniques. Included should be an effective ground simulation and test effort.
There are several issues associated with the space transportation systems implementations, described in the Mars Exploration Architecture, which require further analysis. These issues include:
These issues are described below, along with alternative approaches and recommended focused studies which are critical for follow-on evaluation and architecture selection.
Issue Number: 1
Issue: Lunar Surface Payload Requirement (mass and volume)
The surface payload requirements define the necessary IMLEO capability to complete the lunar missions. Current manifests require large landers and do not provide for a common pilot/cargo sizing capability.
Alternative Approaches:
Evaluation of surface payload requirements with the emphasis on breaking the payloads into the smallest feasible pieces would provide a potentially lower cost transportation system. The sizing philosophy of providing a common system to support cargo and pilot missions results in a more efficient space transportation system.
Recommended Focused Studies:
Part of the transportation sensitivities associated with smaller surface payload requirements will be addressed in the trade "ETO Size vs On Orbit Assembly. vs P/L Requirements." (See Section 4.9, Issue 1)
Issue Number: 2
Issue: Use of the Moon for Mars Dress Rehearsal
The architecture includes a complete dress rehearsal for the mission to Mars to be performed at the Moon in 2008. The dress rehearsal implemented in the white papers is to carry a Mars transit habitat to lunar orbit on the Lunar Transportation System for a long duration stay. This element is probably the only practical Mars hardware element that could be ready in that time frame. A dress rehearsal at the Moon could be a major schedule and cost impact to both the Mars and lunar programs.
Alternative Approaches:
Other options to accomplish the objectives of the dress rehearsal should be considered. Alternate schemes for simulation of Mars missions include ground (Earth) simulations and simulations in Earth orbit.
Recommended Focused Studies: Mars Dress Rehearsal at the Moon
Initially a study is needed to understand the impacts of performing the Mars mission dress rehearsal at the Moon and the most efficient means of providing transportation to meet the requirements. This analysis will determine the appropriate transportation elements required for MTV simulation, descent/ascent simulation, microgravity exposure and long duration crew interaction effects. In conjunction, this trade will also examine the issue of commonality between lunar and Mars transportation elements. The goal would be to determine if a high level of commonality could be achieved in order to provide an inherent Mars simulation with the lunar hardware. The analysis will also look at alternate schemes for simulation of Mars missions, including both ground and Earth orbital.
Issue Number: 3
Issue: Mars Transportation System Nuclear Propulsion for Early IOC
Nuclear propulsion is baselined for the Mars Transfer Vehicle to reduce the transit times, the exposure to zero gravity and space radiation, and mass to low Earth orbit. This architecture has an initial Mars mission in 2012. There is some risk in meeting this date from a technology and political standpoint. It would be prudent to maintain some level of technology effort in alternate propulsion technologies to maintain an early Mars option.
Alternative Approaches:
Alternate propulsion systems could be based on high specific impulse chemical/aerobrake with split/sprint type mission profiles, or perhaps long duration conjunction class missions with artificial gravity systems.
Recommended Focused Studies: Mars Transfer Vehicle Propulsion System
A trade study is recommended to compare nuclear and chemical/aerobrake options using meaningful parameters other than just IMLEO and trip time, which have been the key figures of merit up to this point. Examples of such parameters include mission flexibility, development time/cost and operational complexity. The expected results are a better understanding of nuclear versus chemical/aerobrake propulsion options, including the definition of the key technology needs that should be continued in order to maintain chemical/aerobrake as a viable option.
The following Space Transportation issues were provided by Langley Research Center.
Issue Number: 1
Issue: MEV Entry/Landing System Options
The recommended transportation approach for both architectures uses separate cargo and piloted flights, with both payload classes utilizing nuclear thermal propulsion (NTP) for Mars orbit capture. The cargo and piloted systems must meet on the Mars surface in order to conduct the mission. For this propulsion approach, the Mars entry/landing system is decoupled from the NTP system used for orbit capture. However, the method(s) for providing the precision surface landing/rendezvous is not clear.
Alternative Approaches:
Control of landing site targeting can be provided at and traded between different phases of the entry/landing profile. The three primary phases are: (1) the orbital phase where selection or adjustment of the parking orbit provides control over the reentry initiation location; (2) the entry phase where aerodynamic maneuvers can be used to provide crossrange or downrange; and (3) the landing maneuver where propulsive maneuvers can be used for final trajectory adjustments. The primary configuration and operational options are: (1) Ballistic: L/D of zero, control is provided in phases 1 and 3 with minimal dispersions in phase 2; (2) Low L/D (L/D of 0.3 to 0.5), modest crossrange/downrange capability alleviates constraints on parking orbit; and (3) High L/D (L/D of over 1) provides substantial cross/range however high ballistic coefficient requires large propulsive increment in final landing phase.
Recommended Focused Studies: MEV Entry/Landing
The range of potential entry/landing concepts should be compared for their ability to meet precision landing/ rendezvous requirements.
Issue Number: 2
Issue: Mars Transfer Vehicle (MTV) Propulsion System
The Synthesis Group recommended approach for Mars transfer propulsion, regardless of the architecture and regardless of the payload (manned or unmanned cargo), is a nuclear thermal propulsion (NTP) system. The NTP performance, which enables the use of more energetic trajectories to reduce crew transit times, is not required for the unmanned, one-way cargo missions. Also, the reference mission scenarios include only one opposition class piloted mission before transitioning to a less demanding conjunction class mission. Does one opposition class mission provide sufficient justification for development of a NTP?
Alternative Approaches:
A modular MTV propulsion system which provides configuration options to meet the different requirements of the manned and unmanned mission elements may provide a better solution than a single propulsion system. Hybrid propulsion systems which combine NTP and chem/ aerobrake modes in series should be evaluated for both manned and cargo elements. For the minimum energy cargo transfers, the relatively low Mars approach velocities make aerobraking particularly attractive because the aerocapture conditions are only slightly more demanding than the entry from orbit. Existing thermal protection materials can easily meet this requirement and a low (0.3) L/D provides adequate performance. By using the same aerobrake for aerocapture and orbital entry, orbital insertion is achieved at a very low weight cost. For the manned mission, the hybrid propulsion concept uses NTP for only the initial trans-Mars injection and uses chem/aerobraking for the subsequent propulsion events. Comparable mission performance is achieved while greatly simplifying the NTP long duration operations.
Recommended Focused Studies: MTV Propulsion
Compare transportation system with single high performance propulsion system to a modular transportation system which can be configured to specific mission performance needs. The issue of hybrid propulsion (combinations of nuclear and chem/aerobrake) options are being assessed in a LaRC/LeRC/ MSFC trade study.
Issue Number: 3
Issue: Mars Orbit Capture
The synthesis report recommended approach is to use NTP burns to achieve Mars orbit.
Alternative Approaches:
A combination of aerocapture and Mars excursion vehicle (MEV) chemical propulsion may offer improvements in mission safety, cost, and performance. The policy regarding possible nuclear contamination of the Mars environment is yet to be established as are guidelines as to how much is permissible. Projections of contamination to be expected are also yet to be developed.
Recommended Focused Studies: Mars Orbit Capture
The relative safety, cost, and performance of the combination of aerocapture and MEV chemical propulsion versus NTP should be assessed.
Issue Number: 4
Issue: NTP Reusability
The Synthesis Group Report proposes disposal of the nuclear stage in solar orbit after separation from the crew reentry vehicle returning to Earth. The NTP system will retain considerable lifetime after only one use. Reusability of the NTP stage may offer cost advantages.
Alternative Approaches:
Options include designing for reusability after mission scenarios involving NTP for TMI only or TMI and TEI. Another option involves NTP reusability after Moon missions where Mars hardware is proven by demonstration usage on the Moon.
Recommended Focused Studies: NTP Reusability
The objective of the studies would be principally to develop a consolidated SEI position. Presently, technology, mission scenario and transportation system studies all approach the issue differently as to what is the assumed capability. Developing the capability will have a major impact on the technology development program front-end costs and will require drastically altered, in-orbit supporting infrastructure during mission execution. The assessment must consider total system as well as life cycle costs, performance, safety and schedule.
Issue Number: 5
Issue: Nuclear Thermal Propulsion Validation Flight.
The Synthesis Group Report states the use of the first Mars cargo mission as a validation flight for the nuclear thermal propulsion (NTP) system. This groundrule is related to the Synthesis Group recommendation that, regardless of the architecture and regardless of the payload (manned or unmanned cargo), the Mars transfer vehicle should use NTP.
Alternative Approach:
The method of NTR validation should be assessed against the selected architecture implementation and propulsion systems, and not be a primary architectural requirement. If an alternative propulsion system approach is chosen for the cargo missions because of the much lower energy requirements or for any other reason, this groundrule is highly questionable. An alternate validation approach for NTP which stays in the vicinity of Earth might be better from a cost and technical standpoint if acceptable from an environmental perspective.
Recommended Focused Studies: Alternative Propulsion Options
Recommend incorporation of this issue in studies of alternative propulsion options.
The following Space Transportation issues were provided by Lewis Research Center.
Issue Number: 1
Issue: NEP Space Transportation Systems
Nuclear thermal propulsion has been prematurely selected by the Stafford Committee as the space transportation system for piloted Mars missions. Other advanced propulsion technologies, such as nuclear electric propulsion (NEP), need to be investigated for suitability to all missions of interest.
Alternative Approaches:
Nuclear electric propulsion can offer many benefits to piloted Mars, lunar and Mars cargo, and precursor/robotic mission applications. "Fast" 400 day piloted Mars missions can be performed while leveraging existing SP-100 reactor and electric propulsion technology programs, while more advanced power and propulsion technologies can allow missions of less than one year duration. NEP can efficiently transport cargo to the Moon and Mars, as well as enable demanding robotic missions. Low resupply masses allow even greater mass savings over time for reusable systems. Numerous mission flexibilities afforded by high specific impulses and extended thrusting times (such as continuous abort capability, three-month Earth departure windows, and variable Mars stay times) will greatly enhance crew safety. Programmatically, NEP can benefit from existing reactor and thruster technology programs and commonality with surface power systems. An inherent evolutionary capacity to perform a broad range of near and far term missions, along with the aforementioned performance and programmatic benefits, makes NEP a compelling option from which to develop a space transportation infrastructure.
Recommended Focused Studies: Application of NEP to SEI Space Transportation Systems
Issue Number: 2
Issue: Solar Electric Propulsion Space Transportation Systems
Nuclear thermal propulsion has been prematurely selected by the Stafford Committee as the space transportation system for piloted Mars missions. Other advanced propulsion technologies, such as solar electric propulsion (SEP), need to be investigated for suitability to all missions of interest.
Alternative Approaches:
Solar electric propulsion should be investigated for application to piloted Mars, lunar and Mars cargo, and precursor missions. Utility of using SEP for split/sprint missions should be determined. SEP has the potential to be a long-lived, robust transportation element for space exploration. SEP is very efficient in that its fuel consumption is low, yielding a high payload to total mass fraction. SEP is non-nuclear which allows it to enter low Earth orbit without nuclear safety concerns. It will not need to remain beyond a "safe orbit" distance from the Earth. A cargo vehicle using SEP can transport very large payloads to the Moon or Mars. Mission windows are longer than for nuclear thermal or chemical propulsion allowing greater mission flexibility.
Recommended Focused Studies: Application of SEP to SEI Space Transportation Systems
Issue Number: 3
Issue: Alternative Implementation for Lunar Transportation System
Chemical, "Apollo-style" propulsion has been prematurely selected by the Stafford Committee as the space transportation system for piloted and cargo lunar missions. Other propulsion technologies need to be investigated for suitability to all missions of interest.
Alternative Approaches:
Application of Centaur-derived stages for the lunar transportation system offers the potential of lower cost and lower schedule risk.
Recommended Focused Studies: Application of Centaur-Derived Stages for Lunar Transportation System
A focused study to determine the cost and schedule implication for Centaur-derived stages, within the lunar transportation system, is recommended. The schedule and cost data should be developed for each architecture. The resultant development program and life cycle implications should be compared to a "clean sheet" development.
Issue Number: 4
Issue: Single NTR-Based Lunar/Mars Space Transportation System
A variety of different technologies/Space Transportation Systems (STS) are being examined for both lunar and Mars mission applications. An "Apollo-style" lunar STS will be costly to redo (approx $13-17 billion) and has little applicability to Mars. The Mars STS being examined by MSFC assumes advanced NTR technology levels (T/W=20) for "man-rated" systems and also "customized" vehicle designs, different for each Mars opportunity. The time and cost to develop these varied and multiple systems are expected to be significant.
Alternative Approaches:
A single NTR-based STS for lunar/Mars missions using modular NTR/stage components has been examined at the LeRC and shown to have a number of mission benefits. These include enhanced mission flexibility, reduced development/procurement costs through "standardization" of components, simplicity of design and "in-space" assembly, and a shortened development schedule.
Recommended Focused Studies: Application of NTR to Lunar and Mars Missions
Issue Number: 1
Issue: On-Orbit Operations Planning
The Synthesis Group Report claims that an on-orbit support facility or capability is not necessary. The assembly mission is accomplished by simply mating and docking the few mission elements. It may be possible to develop a 250 mt launch capability; however, it may not be possible to package the mission pieces within the launch envelope in the operational configuration. Mate and dock details are not available, therefore complexity of these operations are undefined.
Alternative Approach:
It is highly probable that some on-orbit assembly or check-out assistance will be necessary for both the lunar and Mars missions. A prudent plan would be to evaluate the mate and dock complexity details, assess alternate launch vehicle lift capabilities and therefore more complex on-orbit operations, analyze on-orbit operations aids either at SSF or on a dedicated facility, and systematically select the "optimum" engineering concept.
Recommended Focused Studies: On-Orbit Operations Planning
Several studies are necessary to generate additional information and to systematically assess this issue:
There are several issues associated with the ETO transportation systems implementations, described in the Mars Exploration Architecture, which require further analysis. These issues include:
These issues are described below, along with alternative approaches and recommended focused studies which are critical for follow-on evaluation and architecture selection.
Issue Number: 1
Issue: HLLV Performance Requirement (Moon/Mars)
The payload to orbit capability should be an output of analysis taking into account the surface payload requirements, operational constraints, and programmatics. The 150 mt lunar vehicle is not fully utilized on every flight, and suggests that there may be a more optimum launch performance requirement than 150 mt.
Alternative Approaches:
Maximum commonality with the National Launch System (NLS) program should be examined. NLS evolution/derivatives should be traded against "clean sheet" approaches.
Recommended Focused Studies: ETO Size vs Assembly Operations vs Payload Requirement
The questions to be addressed are: 1) What launch vehicle size represents the most effective approach (cost, schedule, etc.) to meet SEI transportation needs? and 2) What are the effects of key sensitivities on Space Transportation? The objective of the trade study is to understand the implications and sensitivities of various ETO options to meet the Space Transportation payload and mission rate requirements. The approach is to generate a set of ETO options and vary Space Transportation requirements, then utilize an integrated model to assess the integrated transportation concepts. The evaluation criteria for combination selections will include cost (DDT&E and LCC), schedule availability, ground and on-orbit operations assessment,etc.
Issue Number: 2
Issue: Early IOC for 150 mt HLLV
The development of a new launch vehicle in the early 2000's, in addition to NLS, places significant programmatic burdens on the Agency's resources.
Alternative Approaches:
The issue can be alleviated by slipping the lunar mission schedule or by evolving/deriving the HLLV from the NLS Program (70 mt to 150 mt).
Recommended Focused Studies: No further studies required.
Issue Number: 3
Issue: HLLV Booster Engine Type/Thrust/Propellant
The development of a new Lox/RP HLLV booster and engine in conjunction with a Lox/LH2 core may not be the most cost effective approach to meeting the ETO requirements.
Alternative Approaches:
Several other approaches should be addressed including: all Lox/LH2 system, a Lox/RP first stage + Lox/LH2 second stage series burn vehicle. The engine types include STME, F1-A, ASRM.
Recommended Focused Studies: ETO Trade Studies
Three paths should be evaluated: NLS deriving to 150 mt, NLS evolving to 70 mt then 150 mt, and a "clean sheet" 250 mt evolved down to 150 mt. Propellant options include: solid, Lox/LH2, and Lox/RP in various combinations. STME and F1-A engines will be evaluated for main launch vehicle stages. Lunar upperstage engine options will be: RL10, J2, and STME. Launch system selection will be based on performance, overall cost, operability, and design feasibility.
Issue Number: 1
Issue: Autonomous Telecommunications, Information Systems, and Navigation Test/Demonstration
The Mars dress rehearsal on the lunar surface will require an approximation of the Mars infrastructure to demonstrate autonomous operations. The Synthesis Group report did not include any of the navigation or information systems that would be required to approximate the martian systems. It is not clear how far we have to go in order to prove the concept of autonomous operations. The robotic precursor, cargo, and piloted vehicles will likely require different levels of autonomy, and the robotic missions may not be able to support test and demonstration of autonomous telecommunications, information systems, and navigation systems for piloted missions.
Alternative Approaches:
The Mars in-situ telecommunications, information systems, and navigation infrastructure could be approximated with hardware prototypes or simulated with software at the Moon for the dress rehearsal. Alternative locations, such as Earth and Space Station Freedom, should be considered for systems and operations tests and demonstrations.
Recommended Focused Studies:
The different levels of autonomy and the extent to which robotic missions can be used to test and demonstrate autonomous telecommunications, information systems, and navigation operations for Mars piloted missions needs to be examined. Once the critical tests required for demonstration of autonomous these operations have been determined, the optimal location for the tests/demonstrations needs to be studied.
Issue Number: 2
Issue: Communications coverage for Mars missions
The Synthesis Group Report briefly mentions Mars communications relay satellites. The report calls for reconnaissance orbiters launched in 1998 to serve as communications satellites, and also suggests the use of synchronous relay satellites. With the limited definition of the communications architecture, there are questions concerning whether the connectivity will satisfy the user needs, and the impact of the number and frequency of communications outages on operations.
Alternative Approaches:
Mars communications architectures that use different types of Mars relay satellites and orbits should be considered. Additionally, other potentially useful space-based elements (e.g., solar monitoring satellites) should be analyzed to determine if they can reduce communications blackouts, costs, etc.
Recommended Focused Studies:
The Mars communications analysis should include assessment of communications user needs such as connectivity, data rate, real-time communications needs and storage requirements, etc. Alternative Mars communications architectures should be developed and analyzed to accommodate the potential Mars user requirements. The alternative architectures should then be evaluated based on ability to satisfy user needs.
Issue Number: 3
Issue: Lunar communications architecture
For this architecture, the DSN is baselined as the Earth node for communications beyond Earth orbit. ATDRSS may also have potential for supporting lunar communications, especially as backup or emergency support.
Alternative Approaches:
Recommended Focused Studies:
Studies should be performed to determine lunar communications needs, including data rates, coverage requirements, and estimations of the number of simultaneous users that will require support. Based on the requirements, alternative Earth-Moon region communications architectures, such as DSN, ATDRSS or other implementations, should be considered. Selection of the specific implementation will be based on safety, life-cycle cost, programmatic risk, performance, and schedule priorities.
Issue Number: 4
Issue: Information systems architecture
The Synthesis report recognizes that there is a need for an information system architecture but there is no specific definition of the information system, which will be one of the major cost drivers for SEI. Evolution of the SEI information system to support lunar and Mars missions and increasing levels of automation will be a major challenge and a tremendous cost burden if not planned well and early. In addition, since elements of the systems will be developed and managed independently, informations system standards need to be developed and adopted to ensure that the overall architecture will function properly.
Alternative Approaches:
Alternative levels of automation, control locations, system locations, numbers of systems and facilities, information management, and basic information system functionality approaches must be considered.
Recommended Focused Studies:
An information systems architecture needs to be developed and should include integration of all mission elements including planetary surface systems, transportation vehicle, mission control centers, science control centers, international user control centers, data archives, etc. The activity must begin with an end-to-end determination of the functions and interfaces required for the information systems architecture. The information systems functions will be used to develop alternative architectures, to identify functions that are candidates for automation, performance parameters, etc. Studies should also be initiated to determine how knowledge engineering and/or artificial intelligence technologies can be used to effectively perform information systems tasks.
Issue Number: 5
Issue: Telepresence operations, communications, and data rates
The Synthesis report excludes lunar communications satellites in all architectures and states that lunar surface communications between elements that are outside line-of-sight will be accomplished via the Earth and the DSN. The delay introduced by this approach (~ 5 sec. and up) is believed to be unacceptable for dynamic operations and will exclude locally controlled telepresence operations outside line-of-sight. This could greatly limit remote operations outside the base region and could force the operations to be Earth-based and necessitate technology development. Additionally, the 500 Mbps data rate for telepresence provided in the report is believed to be too high and requires further analysis. Required data rates, particularly the telepresence data rate(s), will drive the communications system and realistic data rates must be determined.
Alternative Approaches:
Telepresence control could be handled solely from the Earth for elements that are beyond line-of-sight communication or the functions performed could be limited by the capability of available technology. Alternatively, a lunar relay satellite would increase telepresence performance and may be required to enable teleoperations between elements on the lunar surface.
Recommended Focused Studies:
A prototype demonstration and/or simulation should be performed to identify telepresence operator performance constraints. Alternative telepresence scenarios which vary in terms of required response time should be considered. Additionally, alternative numbers of channels, types of video, types of data, sensors, and data compression techniques should be considered to determine if any perceptible operator problems result. A technology assessment should be performed to project available technology in the time frame of the lunar missions. The study will identify minimum acceptable data rates, data rate ranges, and maximum acceptable delay for alternative telepresence scenarios. See related issue in Section 4.11, issue number 7.
Issue Number: 6
Issue: Mars in-situ navigation system emplacement/calibration/maintenance
The Synthesis Group report includes a Mars-based navigation segment but does not address the time frame nor the method for emplacement of the radiometric navigation aids (surface beacons and/or navigation satellites). The report stipulates the use of the Earth-based segment for calibration of the Mars surface beacons, but the ability of the DSN to accurately locate the beacons in a Mars reference system will be effected by several factors such as the Mars latitude of the beacon. A beacon located at the pole of Mars would not be observable by the DSN.
Alternative Approaches:
The Mars manifest includes Mars Site Reconnaissance Orbiters, Communications Orbiters, and Surface Rovers. These precursor missions may provide an opportunity for emplacement of components of the Mars-based navigation segment. In conjunction with the DSN, the precursor missions may provide an opportunity for calibration.
Recommended Focused Studies:
A study needs to be performed to determine the feasibility of using the precursor missions for emplacement and calibration of some or all of the Mars in-situ navigation system. Additionally, the feasibility of integrating navigation packages within the precursor vehicles should be examined. Techniques for autonomous navigation satellite ephemeris maintenance should be considered. Study of the use of the precursors must address the extended time intervals between the precursor missions and the first arrival at Mars (~15 years) which has implications for both surface beacons and navigation satellites.
Issue Number: 7
Issue: Landing Requirements for Mars split cargo / piloted missions
The synthesis report requires that multiple cargo missions be pre-deployed to have the emplaced systems activated and checked out autonomously before launching the piloted missions. The piloted missions and later cargo missions will then be required to precisely land near the established outpost. This type of mission approach has never been demonstrated and may prove to be risky with our current knowledge of the martian environment. The synthesis strategy of the split cargo / piloted missions is heavily leveraged on the availability of this technology.
Alternative Approaches:
Recommended Focused Studies:
An integrated performance and risk trade study is required to determine the minimum safe distance of which a cargo and piloted lander can be set down safely near critical habitation modules. This study must take into account:
The results of this study will be used to derive the Mars atmospheric and surface knowledge requirements for precursor missions and any navigation infrastructure emplacement requirements.
Issue Number: 8
Issue: Hazard detection and avoidance for first landing at Mars
Landing site verification for piloted landers is performed by precursor, telerobotic rovers which must land at sites yet to be verified as safe from landing hazards. The interesting landing sites, as selected by the reconnaissance orbiters, may possess rough and irregular terrain. The synthesis group report assumed that the precursors can be safely landed. If an open-loop Viking-style landing is employed, there may be unacceptable risks due to landing hazards such as boulders and craters at the more interesting sites. An early failure in the exploration program due to an unsuccesful landing of the outpost site certification rover is unacceptable.
Alternative Approaches:
The probability of success is dramatically increased by using an onboard hazard detection and avoidance system. This technology has not been demonstrated in non-terrestrial environments and further development is required to characterize performance.
Recommended Focused Studies:
A performance/risk trade between the open-loop landing approach and closed-loop hazard detection and avoidance should be conducted. Further development and demonstration of hazard avoidance technology is required to characterize active vs passive sensor performance in the presence of vehicle dynamics and environmental factors (ie. martian wind/density dispersions, dust and fog covering, etc).
Issue Number: 9
Issue: Surface navigation (Rover)
The Synthesis Group report states that surface navigation of the rovers is to be provided by the Earth system. The long round trip communications delay may make operations of the rover impractical especially since the later pressurized rovers are capable of travelling within a 100 km radius.
Alternative Approaches:
The Mars in-situ navigation system may be able to provide the rovers with surface navigation information.
Recommended Focused Studies:
The ability of the Mars in-situ navigation system to support rover surface navigation should be explored as this may significantly enhance rover mission flexibility and possibly provide higher accuracy position data. The complement of onboard navigation sensors for the rovers should be considered.
Issue Number: 1
Issue: Ground Processing Concept
The Synthesis Group Report made the implied assumption that there would be a launch facility with access as needed. However, the report does not mention how this could be achieved. Current KSC facilities are not sufficient for performing the ground processing required for SEI including large payload integration, processing and storing Mars nuclear reactor payloads, and storing the large amounts of propellants required for SEI. Major new facilities will be required. The complexity of ground operations for launch processing will increase tremendously as the SEI program evolves through the lunar and Mars phases.
Alternative Approaches:
The launch facilities at KSC could be expanded and/or commercial or foreign launch facilities could be used to supplement the KSC facilities.
Recommended Focused Studies: Launch Processing Analysis
A study should be performed to analyze launch processing needs to meet the stringent launch windows specified in the Synthesis Group Report. The study should identify launch processing critical paths, and alternative approaches for ground processing, facility locations, and proposed facilities. The analysis should included development of a payload ground processing concept to assess the facility needs, operations costs, ground processing complexity, and launch schedule processing demands.
Issue Number: 2
Issue: Crew Size Specification
The Synthesis Group Report proposes a crew size of six; however, earlier JSC Mission Operations Directorate (MOD) crew sizing analysis recommended a minimum crew size of four. Crew size is a primary driver to element size, element complexity, and Earth-to-orbit mass requirements. However, it is driven by mission content, human factors, and operational efficiency goals. While it is appropriate to establish a crew size for planning, it is too early to commit to a specific size until all mission and research related data is available. Any increases in crew size above the minimum required to conduct the missions must be well understood.
Alternative Approaches:
Various crew size options should be maintained.
Recommended Focused Studies: Operational Analysis of Mission Crew Size
An activity should be initiated to define criteria for determining crew size, to provide operations philosophies/requirements, and to recommend a minimum crew size based on completion of basic mission objectives for each architecture. The study should collect and understand crew performance and crew activity based on research and test. A mathematical model should be developed to predict crew size as a function of mission and operations guidelines.
Issue Number: 3
Issue: Supportability
The Synthesis Group Report acknowledges that supportability concepts must be implemented concurrently with the mission and system concepts to assure crew safety. It is stated that for crew safety, the program must implement such aspects as: system and consumable margins which reflect resupply rates, system designs which allow crew maintenance or repair, multiple levels of parallel redundancy, etc. Further, they have also addressed the need to develop improved maintenance concepts. The issue is that the Synthesis Group Report did not say how supportability could be implemented.
Alternative Approaches:
Supportability concepts must be addressed early in the SEI program since there are no alternative approaches.
Recommended Focused Studies: Development of Supportability Plan
Begin the process to define, adopt, and implement a supportability strategic plan and continue activities that were begun in FY91. The second piece of this is to prepare for the architecture evaluation activity by generating the data required by the supportability model for this architecture and, when data is available, operate the model.
Issue Number: 4
Issue: Crew Safety Options and Contingency Strategies
The Synthesis Group Report focused on a very limited number of contingency scenarios; therefore, it is not clear that the major potential contingencies have been addressed. As such, we do not believe it can be assured that the current architectures have identified the major issues associated with accommodating the first mission priority of crew safety. Relative to element and system design, the report does not indicate whether elements should be designed for the nominal case or if the designs should be driven by contingency considerations.
Alternative Approaches:
Mission elements could be designed for nominal missions, thus taking the associated risks of this approach. Alternatively, systems could be designed for all and/or selected contingencies from which nominal mission capability would be extracted.
Recommended Focused Studies: Development of Contingency Strategies
A study should be performed to (1) identify the major contingency scenarios, and (2) develop and analyze feasible contingency countermeasures to determine abort, crew rescue, and element design concepts and requirements. Several contingency scenarios should be analyzed to determine recovery procedures, safe haven requirements, abort requirements, rescue requirements, etc. A contingency scenario strategy map will be developed to relate specific contingency scenarios to appropriate contingency procedures.
Issue Number: 5
Issue: Earth-To-Orbit Transportation
The Synthesis Group Report assumed an Earth-to-orbit (ETO) transportation system that consisted of current Shuttle fleet, current ELV's, and a Saturn-V derived heavy lift launch vehicle. It also assumed that the ETO infrastructure and vehicle access would be available as required and would be adequate. It is not obvious that the Synthesis Group Report has factored in use of the infrastructure required to put man and cargo into orbit for both SEI and non-SEI missions.
Alternative Approaches:
The ETO capability during the SEI time frame will probably be evolving. Some evolutionary paths may have less impact than others.
Recommended Focused Studies: Operations Analysis of SEI Space Transportation Systems
Perform an operations analysis of the space transportation needs during the SEI time frame. The study should establish baseline requirements for an integrated space transportation system, define an ETO traffic model, and identify ground support facility requirements. Manifests for SEI which reflect a credible mass to Earth orbit flight rate, operations, etc. need to be developed concurrently.
Issue Number: 6
Issue: Training Facilities
The Synthesis Group Report proposes training facilities that promulgate a business-as-usual approach to operations (i.e., motion base simulators, etc.), while some high fidelity vehicle simulators may be required.
Alternative Approaches:
Innovative training systems such as computer based training, virtual reality, etc. may provide adequate training at a lower cost.
Recommended Focused Studies: Effective Training
Assess innovative training techniques which will provide effective crew and ground personnel training while reducing operations costs yet assure crew safety and mission success. This assessment should include the identification of the skill needs of future crew persons and alternative training techniques for meeting these needs. Based upon this analysis, training hardware and facility requirement estimates can be made.
Issue Number: 7
Issue: Automation and Robotics
The Synthesis Group Report assumes extensive use of telepresence techniques. It is not obvious that this is the best approach for accomplishing all tasks.
Alternative Approaches:
Depending upon the task, EVA, IVA, telerobotic, automated methods, etc. may be preferred.
Recommended Focused Studies: Analysis of Automation Levels
Using Shuttle, Space Station, and SEI data and studies, identify tasks or task groups that require some level of automation. Develop a data base from which operations task analysis can be performed. Utilizing this data, perform an architecture specific analysis of selected SEI program tasks such as the assembly of a surface habitat to determine the proper mixture of automation, robotics, telerobotics, or EVA operations. See related issue in Section 4.10, issue number 4.
Issue Number: 8
Issue: In-Space Operations and Assembly
The Synthesis Group Report indicates that in-space operations and assembly will be required for SEI, particularly for manned Mars missions when the vehicle is assembled and launched from Earth orbit. The issue is that the report does not describe how these operations could be implemented.
Alternative Approaches:
Alternative techniques for performing cryogenic fuel transfer and management, robotic assembly, and vehicle health maintenance must be assessed to identify the technologies that best suit required SEI in-space operations and assembly tasks.
Recommended Focused Studies: In-Space Operations and Assembly
The in-space operations and assembly activity should include both trade studies and on-orbit tests with hardware experiments and prototypes. Initial studies should include an analysis of how existing technology, such as technology in use on oil platforms, could be applied to in-space operations. Much of the construction, testing, verification, and maintenance performed on today's oil platforms is done by robotic means in a harsh environment. It will be very useful to see if and how existing systems could be used for in-space operations. Additionally, a proof-of-concept Shuttle hardware experiment should also be initiated to demonstrate numerous key technologies required for SEI missions. This initial experiment is intended to employ fine manipulator robotic techniques for utility and structural connections, employ self-test and checkout operations to verify structural and utility connections, obtain information for development of an on-orbit cryogenic boil-off database, and develop fuel management and transfer techniques.
The final two pages of this Appendix present a heliocentric orbit plot of each of the human exploration trajectories. The view is from the north pole of the celestial sphere looking down onto a projection of the trajectory onto the ecliptic plane. The first point of Aries, designated by g (small sigma), is shown for inertial reference.