Figure 1 - LUNOX Space Transportation Elements: STS-Derived Launch Vehicle, Cargo Lander, Piloted Lander
Lisa A. Guerra
Advanced Planning and Analysis Division, Science Applications International Corporation, 400 Virginia Ave., S.W., Washington, DC, 20024
In the current environment of controlling and justifying initial program expenditures, large investments made with the intent of reducing future costs are not always acceptable. The concept outlined here relies upon lunar-produced oxygen (LUNOX) for round-trip piloted missions beginning with the first flight. The performance leverage is invested in reducing the size and complexity of the transportation systems and therefore their development costs. The economies in transportation production costs will accrue immediately. It is expected that the development and deployment costs associated with the LUNOX infrastructure will be offset by a combination of reduced transportation development and production costs after a "reasonable" number of flights.
To test these assumptions, two alternative lunar exploration scenarios have been developed. Both result in comparable lunar surface capabilities and space transportation requirements, but one utilizes the early LUNOX concept while the other does not. The development and production costs of the hardware associated with each scenario were estimated using the NASA Johnson Space Center's Advanced Mission Cost Model (Cyr, 1988), along with a statistical measure of confidence in the results.
Two techniques for attaining these capabilities will be described next. The first utilizes early lunar propellant production in an attempt to reduce development and production costs, the second relies on a more traditional approach.
It is not possible at this point to identify the "best" extraction technique for early LUNOX production. Trades involving system mass, power requirements, process complexity, oxygen yields, reagent resupply, and equipment maintenance must be made. However, it was decided to adopt the ilmenite reduction process as a reference since a design study has been done for a processing plant consistent with the production quantities required by this analysis (Christiansen 1988). This concept uses the combination of a small teleoperated front-end loader and regolith hauler to mine and transport feedstock and dispose of process tailings, a three-stage fluidized bed reactor to reduce the ilmenite, and a 40 - 60 kWe nuclear power supply.
Space Transportation To derive the maximum benefit of LUNOX, the strategy proposed here conducts round-trip piloted missions using a lunar landing vehicle which is designed to land with "dry" liquid oxygen (LO2) tanks (plus flight performance reserves). The lander must carry enough liquid hydrogen (LH2) for the round trip, but the LO2 tanks are refilled on the lunar surface for the return to earth. The resulting gain in performance alters most of the rules of lunar transportation: lunar-orbit rendezvous is no longer advantageous since the penalty of carrying the earth-return propellant to the lunar surface is essentially eliminated, and even staging on the moon offers little advantage. This allows development of a single crew module (essentially a scaled-up Apollo Command Module), and a single service module/lander combination. Most importantly, this mission concept decreases the trans-lunar injected spacecraft mass to the point that a piloted flight can be accomplished with a single launch of a Space Transportation System (STS)-derived launch vehicle. The LUNOX space transportation elements are shown in Figure 1.
The LUNOX production equipment, habitation elements, and exploration systems must be transported by dedicated cargo flights, as the piloted lander can provide only a few tons of cargo and remain within the lift capability of an STS-derived launcher. If the same launch vehicle and TLI stage are used for both piloted and cargo missions, a delivery capability of approximately 12 metric tons to the lunar surface results.
Figure 1 - LUNOX Space Transportation Elements: STS-Derived Launch Vehicle, Cargo Lander, Piloted Lander
Surface Systems A typical lunar outpost buildup scenario requires the delivery of a habitat module which may mass from 17 to 30 tons, depending upon the level of outfitting. This exceeds the cargo capability of the LUNOX transportation system, so a strategy utilizing a combination of pressurized rovers and small, specialized modules to establish surface habitation has been developed.
Previous rover conceptual designs based upon requirements to support a crew of two for a lunar day and transport them hundreds of kilometers (Davidson 1988), have been adopted for the present work. Since the vehicles must provide power, communications, thermal control, life support, and habitation volume as part of their prime mission, it is reasonable to take advantage of these features when the rovers are parked at the outpost. While the rovers can provide or augment many of the surface capabilities needed, they probably cannot supply the kind of robust EVA support that lunar missions will require. Therefore, a combination EVA support and airlock module will be required. This module could also allow pressurized connections to the rovers, logistics containers, and future expansions of the habitable volume. Finally, items such as crew consumables, system resupplies, and maintenance articles may require a pressurized environment. A logistics module which can be transported and docked to one of the pressurized volumes should suffice.
All of the components identified above have masses consistent with the delivery capabilities of the LUNOX launch vehicle and cargo lander. The technique used to integrate them on the lunar surface is outlined next.
Outpost Buildup The initial cargo flight delivers the LUNOX production plant and the nuclear power supply. The plant utilizes the lander frame for structural support and the empty propellant tanks for LUNOX storage. The reactor, mounted on a small teleoperated cart, is deployed from the lander and is translated away from the plant, trailing a power cable with attachments for multiple connections. The second cargo flight delivers the teleoperated surface vehicles required for regolith and liquid oxygen transport, and LUNOX production begins at this time.
The habitation infrastructure emplacement begins with the third mission and the delivery of the first pressurized rover. Once unloaded onto the lunar surface, it is remotely driven to the future outpost location. This process is repeated with the fourth flight. The airlock/EVA support module, transported on Flight 5, is mounted on a wheeled chassis and is also remotely driven to serve as the "hub" of the outpost assembly. The components can now be configured in the arrangement shown in Figure 2, or if this is deemed too complex an operation to be accomplished through teleoperation, it can be performed by the first lunar crew. The final cargo flight prior to IOC delivers consumables, spares, and any equipment required for additional outfitting. The facilities are now in place to support six-week, four-person missions. The LUNOX manifest is shown in Table 1.
Figure 2 - LUNOX systems at IOC
| Cargo Flight 1 | 12379 kg | |||
| LUNOX Plant | 7269 | |||
| Nuclear Reactor | 5110 | |||
| Cargo Flight 2 | 8322 kg | |||
| Tanker (2) | 2942 | |||
| Loader (2) | 3456 | |||
| Hauler (2) | 1924 | |||
| Cargo Flight 3 | 7694 kg | |||
| Pressurized Rover | 5150 | |||
| Mobile Power Unit | 1544 | |||
| Science Payload | 1000 | |||
| Cargo Flight 4 | 7694 kg | |||
| Pressurized Rover | 5150 | |||
| Mobile Power Unit | 1544 | |||
| Science Payload | 1000 | |||
| Cargo Flight 5 | 11010 kg | |||
| Airlock/EVA/Node | 11010 | |||
| Cargo Flight 6 | 12454 kg | |||
| Logistics | 12454 | |||
From this description of the LUNOX strategy, it is apparent that its feasibility relies heavily upon the development of key technologies: high duty-cycle electric surface vehicles for regolith and cargo transport, automation and robotics for mining and surface system integration, and extraterrestrial chemical processing for unattended lunar oxygen production. This is somewhat of a departure from the technology expertise of the aerospace industry where the focus tends to be in the area of vehicle and propulsion systems. However, this can be viewed as an opportunity to broaden the relevancy of government-sponsored space technology to the commercial sector. In addition, the programmatic risk associated with the oxygen extraction techniques can be mitigated by proof-of-concept precursor missions involving small lunar landers equipped with process demonstration packages.
The lunar surface habitat was designed to be delivered to the moon with a single launch and to automatically activate all needed systems upon landing. It was derived from a Space Station Freedom Program habitat module design and featured an airlock, a photovoltaic/regenerative fuel cell power system, thermal control system, logistics storage volume, and a spacesuit maintenance facility integrated into a single unit (Woodcock 1993). To eliminate the need for massive unloading equipment and to avoid the associated surface operations, it was decided to leave the habitat integrated with the lunar lander, as shown in Figure 3.
To accommodate the requirement for long-range surface roving, pressurized rovers with the same characteristics as those used in the LUNOX scenario were proposed. While the vehicles were not integrated into the habitat structure, they did depend upon the habitat power system for recharge. Table 2 gives a mass breakdown of the two required cargo flights.
The pre-integrated nature of the lunar habitat, combined with the desire to avoid on-orbit operations and multiple launches, resulted in the requirement for a large new launch vehicle design. A concept derived from the Apollo-Saturn vehicle is shown in Figure 4. A single lander design was utilized for both cargo and piloted flights (Kahl 1993). When used in the piloted mode, the payload was replaced by an earth-return stage and the crew module.
| Cargo Flight 1 | 30785 kg | |||
| Hab Module | 30785 | |||
| Cargo Flight 2 | 24754 kg | |||
| Pressurized Rover (2) | 10300 | |||
| Science | 2000 | |||
| Logistics | 12454 | |||
Figure 3 - FLO Lunar Habitat
Figure 4 - FLO Launch Vehicle
The parametric inputs required by the AMCM for each system include the dry mass, the number of development articles, the number of production units, the year of initial operational capability, and the difficulty factor (measure of technical and programmatic difficulty). For the difficulty factor, rather than the mission designer selecting a value assessed relative to other similar historical systems, a separate survey was issued to capture the system manager's technique for project and engineering management.
The survey designates the categories of interest, such as design complexity. For each category three choices are available representing "ways of doing business", from business as usual (approximately like the Space Shuttle Orbiter) to aggressive business practices (like the X-24 and Project Mercury). The system managers treated the survey like a shopping list, selecting one response for each line item under programmatic and technical difficulty. The values for each selection were averaged to arrive at a programmatic difficulty factor and a technical difficulty factor.
In addition to providing a baseline cost estimate for LUNOX and FLO, this study included a range for both scenario costs based on mission design uncertainty. The cost uncertainty analysis involved applying a risk model to the AMCM (Palisade Corp. 1992). The uncertain input variables modeled with probability distributions included difficulty factor, dry mass, and development quantity. Latin Hypercube simulation was used to arrive at the probability distribution for the total LUNOX and FLO costs.
| LUNOX | FLO | |||||
|---|---|---|---|---|---|---|
| Launch Vehicle | 4.5 | 23% | 12.6 | 50% | ||
| Space Transportation | 6.9 | 35% | 7.3 | 29% | ||
| Habitation Systems | 0.0 | 0% | 2.1 | 9% | ||
| LUNOX Systems | 3.4 | 17% | 0.0 | 0% | ||
| Surface Systems | 4.0 | 21% | 1.9 | 8% | ||
| Science Payloads | 0.8 | 4% | 1.1 | 4% | ||
| Total | 19.6 | 25.0 | ||||
The disparity is obvious in the two launch vehicle estimates, with the FLO launch vehicle consuming 50% of the resources as compared to 23% for LUNOX. Table 4 highlights the specific launch vehicle element costs to emphasize the difference between an STS-derived, 80 metric ton-to-LEO vehicle and a new, 240 metric ton vehicle. The values displayed in this table include the development costs and the flight production costs for three FLO launches (two cargo and one crew) and seven LUNOX launches (six cargo and one crew).
| LUNOX | FLO | |||
|---|---|---|---|---|
| Core | 1.7 | 3.9 | ||
| Main Engines | 0.9 | 1.2 | ||
| Boosters | 0.4 | 3.0 | ||
| Second Stage | 0.0 | 2.3 | ||
| TLI Stage | 1.2 | 1.5 | ||
| Shroud & Integration | 0.3 | 0.7 | ||
| Total | 4.5 | 12.6 |
Figure 5 further highlights the distribution of costs between LUNOX and FLO through the initial operational capability. The development costs for all the transportation systems and the surface systems are distinguished from the production/flight costs. Again, the LUNOX scenario has the larger share for surface system (cargo) development and production; FLO maintains the larger share for transportation.
Figure 5 - Prime Costs through IOC
Figure 6 - Piloted Prime Costs
Figure 7 - Cargo Prime Costs
Figures 6 and 7 display the costs associated with piloted transportation and cargo transportation to the moon, respectively. The piloted transportation graph assumes the development costs for the launch vehicle, in both approaches. The first piloted mission to the moon in FLO costs approximately $4 billion, while the same crew of four to the moon in LUNOX costs approximately $1.5 billion. Since the same launch vehicle and lunar descent stage are required for FLO piloted missions as FLO cargo missions, there are no development costs attributed to FLO in Figure 7. The LUNOX development cost refers to the cargo descent stage. The first cargo mission to the moon in FLO costs approximately $3.2 billion (delivering 32 mt), while the first cargo mission in LUNOX costs almost $1 billion (delivering 12 mt).
Figure 8 projects the prime cost for follow-on piloted missions to the moon for both approaches. The cost of an additional piloted flight includes the launch vehicle, TLI stage, and lunar lander. The FLO piloted lander has the capacity to transport the crew's logistics for their 42 earth-day stay. In contrast, the LUNOX approach requires an additional cargo landing for every two piloted missions in order to deliver the essential logistics. In Figure 8, flight numbers 3 and 5 for LUNOX include the cost for two additional cargo flights. As previously noted, the cost delta after the first piloted flight is approximately $5 billion. After six piloted flights the cost delta between FLO and LUNOX is approximately $18.5 billion. Additional oxygen production infrastructure, beyond IOC capability, was not included in this estimate for LUNOX. Further analysis regarding the compatibility between the oxygen production rate and the LUNOX mission flight rate is required.
Figure 8 - Post-IOC Costs for Continued Piloted Missions
Probabilistic uncertainty analysis allows program managers to discuss confidence levels for cost estimates and ultimately the amount of reserve to carry for such a mission. The cost S-curve gives the probability of a project's cost not exceeding a given cost estimate. Figure 9, the cost S-curve or cumulative probability distribution, clearly demonstrates the confidence levels for: 1) the AMCM-modeled estimate for FLO at about 17% and for LUNOX at about 20%, 2) the simulation means, and 3) the 90% confidence values. The steepness of the S-curve signifies how much the level of confidence improves when a small amount of reserves is added. From Figure 9, it is evident that the LUNOX curve is more steep than the FLO curve, thus emphasizing a more manageable cost risk in the LUNOX mission approach. Furthermore, the 90 percentile confidence value for LUNOX is approximately equal to the mean value for FLO.
Figure - 9 LUNOX and FLO Total Program Cost Cumulative Distributions
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