kaplan@snmail.jsc.nasa.gov
The following material is extracted from the Martin Marietta report issued at the end of the contract. The Martin Marietta authors are Robert Zubrin, Steve Price, Larry Mason, and Larry Clark:
"Prior to the project reported on here, a study, also funded by the [Planetary Missions and Materials Branch] of JSC, had been undertaken at Martin Marietta, to examine the benefits and feasibility of accomplishing a Mars Sample Return (MSR) mission using locally produced propellant to fuel the rocket vehicle that would return the sample to Earth. That study, led by Robert Zubrin, found that a large mission enhancement could be achieved by such means, and recommended that the propellant production process employed be one termed the "Sabatier/Electrolysis" or "S/E" cycle. Using such a system, it was found that an S/E unit producing 1 kg of propellant per day could be used to support an MSR mission that would return a 4 kg soil and rock sample from Mars to Earth. A single Delta 7925 launch vehicle was found sufficient to support the mission, which consisted of a single spacecraft being sent directly from Earth to the Martian surface, refueling there during a year and a half surface stay, and then returning directly from the Martian surface to Earth, without any intervening Mars orbit rendezvous maneuver.
"The S/E cycle propellant plant employed in the mission works as follows: Hydrogen is transported from Earth to Mars where it is combined with CO2 acquired from the Martian atmosphere in a Sabatier reactor to produce methane and water in a 1:2 molar ratio. The methane produced by this process is drawn off and liquefied, while the water is condensed and sent to an electrolysis unit to be split into hydrogen and oxygen. The oxygen produced by the electrolysis unit is liquefied, and the hydrogen is fed back into the Sabatier reactor.
"The technology required to accomplish this cycle is well understood, and in fact has been in use on Earth for over a century. This high degree of heritage of the required component technology was the basis for the selection of the S/E cycle for the MSR mission. However, despite the fact that each of the component technologies has long been used, to the best of our knowledge, putting all of them in a cycle to make a complete system of the type described has never been done."
". . . In the course of just three months, with a total budget of $47,000, a full scale working system was built and made to operate with a conversion efficiency of 94%. The combined mass of all operating components of the prototype S/E system was less than 20 kg, with potential improvements that would cut that mass roughly in half clearly in sight. The output of the current prototype system, 720 grams of propellant a day, would allow it to produce close to 20 times its own weight in propellant in the course of a typical 500 day conjunction class Mars surface stay."
". . . Much work remains to be done before the complete practicality of in-situ propellant production to support Mars missions is demonstrated end-to-end. Yet the relative ease with which so much was accomplished in so short a time on the present project can only be viewed as extremely encouraging. Taken together with the enormous benefits in-situ propellant production provides to both automated and piloted Mars exploration, the success of the current demonstration speaks forcefully for the wisdom of further development efforts."