Challenger II is a sample return mission concept using In-Situ Resource
Utilization (ISRU); After Columbia Project's entry into the MarsDrive Contest. ISRU was originally conceived by
Dr. Robert Zubrin in 1989 for a piloted mission plan entitled Mars Direct by putting together three industrial chemical reactions
in a relationship capable of producing oxymethane propellants using seed hydrogen brought from Earth with locally acquired
carbon dioxide. Zubrin went on to found Pioneer Astronautics, Inc. to further explore propellant ISRU chemistry. Mars Challenger II uses two elements, the Judith Booster and Christa Rover, which
are launched together on a common launch vehicle and cruise stage, but are landed separately on Mars near each other
in the Marte Vallis region, where there are recent Amazonian era water channels and the small possibility of
discovering current life.
dominant element is the Judith Booster and its accompanying fuel plant capable of compressing locally acquired carbon dioxide
for use in an oxybenzene propellant reactor. The use of the more complex and high performance oxybenzene ISRU is the
only design decision altered from the original Mars Challenger. The original
design explored the Sabatier/Electrolysis process for oxymethane propellants, and revealed major, but managable problems using
the booster's ascent tanks for outbound hydrogen storage. In exchange, Mars Challenger
II experiences problems with the physical properties of benzene in the cold Martian environment.
Christa Rover is unchanged. It is landed
up to several kilometres away from Judith and uses its suite of scientific instruments
on route to the booster to examine sites and select samples. As with the original,
Mars Challenger II uses the strategy of determining that samples selected for return to Earth do not contain life harmful
to our biosphere.
reasons of cost and politics, both craft are electrically powered by solar arrays, with a small amount of nuclear radioisotope
material in heating units, Christa's scientific spectrometers, and the control sample sterilizers for its laboratory style
technologies and off the shelf or derived hardware will be used throughout to keep development and qualification costs to
a minimum, however several technologies must be converted from terrestrial and experimental equivalents into flight hardware,
and protecting the mission's biological integrity is expensive in any case. For example, the development of
hydrogen compatible ascent tanks must be done from scratch. The author is convinced that this mission can be accomplished
for $1200 million on a six year schedule.
The report for the Mars Challenger II is available here:
Paying Your Way Home: Making Fuel on Mars for Sample Return Missions
Presented at the Canadian Space Summit on 17 November 2007 at 16:10 MST in Room 105 of the Science
B building at the University of Calgary
In-Situ Resource Utilization (ISRU) is, quite simply, the use of local, as opposed to imported,
resources in the accomplishment of a mission goal. It goes beyond using simply environments, such as in aerobraking,
gravity slingshots and solar pressure, to actually retrieve and process material. It also should not be confused with
component level repair, closed cycle life support, and staged logistics. The generic chemistry model for Mars ISRU is
to bring along stored liquid hydrogen and combine it with carbon from the Martian carbon dioxide in the atmosphere to form
a hydrocarbon fuel. The oxygen is liquefied to form the oxidizer. It isn't exactly like this in any of the options
available, but it does describe the overall result of the combination of reactions used. The popular hydrocarbons are
methane (CH4) and ethylene (C2H4). As far as the author is aware, Mars Challenger II is the first to study the use of
benzene (C6H6) in a mission design (Pioneer Astronautics has tested it on a demonstrator basis.) It is implicit in many
human mission designs that the same tanks are used to bring the hydrogen to Mars as are used to store the finished propellants.
Actually doing this is harder than it sounds, since a tank must be empty of hydrogen before produced propellants can be put
into it, and hydrogen also has a tendency to combine with and embritle common tank materials, such as titanium. Mars
Challenger II has attempted to answer all of these questions, and may be the first design concept to do so.
Presentation File: http://aftercolumbia.tripod.com/css0711.pdf
On the presentation: I went into this presentation really having only three major
points to make: the basics of how Mars hydrocarbon propellant ISRU worked, how much it could benefit the performance of a
sample return mission, and how much of a pain it would be. These points are on slides 2, 3, and 4 (slide 1 being the
title slide.) After seven minutes, I opened the floor to questions (the presentation was scheduled to last only 25 minutes,
including questions.) The remaining ten slides were to help me answer the most likely questions. One was about
how the chemistry worked, (Slide 5) and a followup from a different member of the audience was "what does F-T stand for?"
Another question (I'm dignifying it a bit, since the asker didn't know that sorption
compressors were being rigorously persued elsewhere), "why don't you use a calcium oxide sorption compressor?" That
presented slide 10. The answer was that I don't know them well, and didn't have enough time and manpower to study all
the options. I also mentioned that sorption compressors do have some choice as to the chemistry. I forgot to mention
the cryocompressor (freezing carbon dioxide into a chamber, and then vaporizing it after sealing the chamber.) All the
reactions wound up being presented, but slides 7, 8, and 9 got "missed" by the questions.