The NASA Exploration Program Office (ExPO) at Johnson Space Center in Houston, Texas, commenced the Mars Exploration Study Project in the summer of 1992. Its aim was to determine how its First Lunar Outpost (FLO) plan (top link below) might find hardware commonality with a follow-on Mars program, thereby reducing the costs of both programs. Mars Exploration Study Team (MEST) workshops held in August 1992 and May 1993 produced a Mars Design Reference Mission (DRM) with little overt FLO commonality beyond outwardly similar conical capsules for lunar and Mars ascent/Earth reentry and an uprated variant of the FLO heavy-lift rocket. In fact, NASA's 1993 Mars DRM owed much to the 1989-1990 Martin Marietta Mars Direct mission plan championed by engineer Robert Zubrin, which bypassed the moon entirely.As the MEST began its study, the Space Exploration Initiative (SEI) that spawned it was drawing to a close. The MEST's labors spanned the 1992 election, in which Republican incumbent George H. W. Bush lost to Democratic challenger William J. Clinton. Many space initiatives begun under Bush would continue and expand under Clinton - for example, U.S.-Russian space cooperation and the Discovery Program of low-cost robot explorers - but SEI, never popular, was not one of them.
NASA halted almost all DRM work by the summer of 1993, and would not begin again to study how human explorers might reach Mars until after the 1996 announcement that possible microfossils had been found in martian meteorite ALH 84001. In 1997, NASA designated its 1993 DRM "DRM 1.0" when it published a new DRM that it designated DRM 3.0. Odd as it may seem, there was no official DRM 2.0, though in at least one NASA document a "scrubbed" (mass-reduced) version of DRM 1.0 bears that designation.
The 1993 DRM's "FLO-class" heavy-lift rocket would be capable of boosting about 240 tons into a 500-kilometer circular low-Earth orbit (LEO). This would make the giant rocket more than twice as powerful as the Apollo-era Saturn V and nearly a quarter again as powerful as the booster used to launch FLO payloads.
NASA's first manned Mars expedition would need four flights of the uprated FLO-class heavy-lift rocket. Three heavy-lifter flights would suffice for each subsequent Mars expedition.
The MEST selected the September 2007 Earth-Mars transfer opportunity to begin its first manned Mars mission because it would be challenging in terms of the amount of propulsive energy required to launch payloads toward Mars. Three unmanned uprated FLO-class rocket launches in rapid succession would begin the mission. All payloads would have a mass at launch from Earth of between 60 and 75 tons.
The MEST decided that its Trans-Mars Injection (TMI) rocket stage, which would launch all DRM payloads out of Earth orbit toward Mars, should employ a nuclear-thermal rocket engine. The liquid hydrogen-fueled stage would be capable of boosting about 100 tons to Mars orbit and about 60 tons to Mars's surface.
The first uprated FLO-class rocket would launch an unmanned Earth-Return Vehicle (ERV) Mars orbiter. The ERV would include a cylindrical, two-deck habitat (hab) module similar to the one on the hab lander that would transport the first crew to Mars in 2009, a Trans-Earth Injection (TEI) stage, and solar arrays for generating electricity. Its TEI stage would carry liquid oxygen and liquid methane propellants for two modified RL-10 rocket engines that would launch the crew home to Earth after their Mars surface mission.
The second giant rocket would launch an unmanned fuel factory/Mars Ascent Vehicle (MAV) lander. The lander, which would carry liquid hydrogen feedstock and a nuclear reactor for MAV propellant manufacture, would deliver about 40 tons of cargo to the landing site on Mars, including a large pressurized rover for long (1000-kilometer) Mars surface traverses.
The third uprated FLO-class rocket launched in the September 2007 opportunity would place into Earth orbit an unmanned hab lander. A twin of the lander that would transport the first crew to Mars in 2009, it would include a regenerable (recycling) life support system and would rely for electricity on a small nuclear power source.
All three payloads would include bowl-shaped aerobraking heat shields (near the end of the 1993 DRM design process, the MEST adopted a bullet-shaped biconic heat shield design). The payloads would reach Mars in August-September 2008 and aerobrake in its atmosphere to shed speed and capture into orbit. The ERV orbiter would then discard its heat shield. The fuel factory/MAV and hab lander would ignite rocket motors to slow themselves and fall into Mars's atmosphere. Following a fiery descent toward their target landing site, they would each discard their heat shield, ignite landing rocket motors, and extend landing legs.
After the fuel factory/MAV lander touched down, a nuclear reactor would lower to Mars's surface on a small rover and trundle away trailing power cables under telerobotic guidance from controllers on Earth. The rover would place the reactor in a crater about 500 meters from the lander. The crater's upraised rim and distance would protect the landing site from radiation the reactor would produce after start-up.
Electricity from the reactor would power the fuel factory, where liquid hydrogen would be exposed to martian atmospheric carbon dioxide in the presence of a nickel or ruthenium catalyst, yielding liquid methane and water (bottom link below). The methane would be stored and the water electrolyzed to yield oxygen and hydrogen. The oxygen would be stored and the hydrogen recycled to manufacture more water and methane.
In one year, the fuel factory would produce and store 5.7 tons of liquid methane and 20.8 tons of liquid oxygen. The MAV would burn these during its ascent to the orbiting ERV at the end of the first Mars crew's surface mission. As a safety measure, the crew would not leave Earth until after the 2007 fuel factory finished making their ascent propellants. The fuel factory would then manufacture a 600-day supply of life support consumables (14.4 tons of water, two tons of nitrogen/argon, and three tons of breathing oxygen).
Meanwhile, the unmanned hab lander would set down nearby. Controllers on Earth would activate and monitor its systems to ensure its readiness for the first Mars crew.
Assuming that the 2007 payloads remained healthy, three more heavy-lift rocket launches would occur during the October-November 2009 Earth-Mars transfer opportunity. One would place into Earth orbit the habitat lander carrying the first six-person Mars expedition crew. The other two would launch an unmanned Earth-return vehicle (ERV) orbiter to serve as a backup for the 2009 first Mars crew or as the primary ERV for the 2012 second Mars crew and an unmanned fuel factory/MAV lander that would provide a backup for the 2009 crew or serve as the primary fuel factory/MAV for the 2012 crew. Following insertion into Earth orbit, TMI stages would boost the three payloads toward Mars.
The crew would reach Mars in about 180 days and aerobrake into a 250-by-34,000-kilometer orbit, then descend to a landing near the 2007 habitat and fuel factory/MAV. Soon after the crew landed, the 2009 fuel factory/MAV and ERV would aerobrake into Mars orbit. The 2009 fuel factory/MAV could be directed to land near the crew if they determined that its 2007 counterpart would be incapable of launching them into Mars orbit at the end of their surface stay. Otherwise, it would land at a new landing site within range of the 2007 pressurized long-traverse rover (that is, no more than 1000 kilometers away) and begin making propellants and life support consumables.
If their hab lander suffered damage during landing, the first crew would abandon it and move into the waiting 2007 hab. If it landed safely, however, the explorers would lower wheels and raise landing gear on the 2009 and 2007 habs and tow them together using an unpressurized rover. They would then link the twin habs with a pressurized tunnel, lower the landing gear and raise the wheels, and set up a greenhouse for growing vegetables to supplement their 800-day supply of dry food.
The first Mars outpost thus established, the astronauts would unpack the pressurized rover from the 2007 MAV lander. The nuclear- or methane/oxygen-powered rover would include a rear-facing docking port for linking to the habs, providing the explorers with additional pressurized living volume while the rover was docked and allowing easy movement between habs and rover. During their planned 600-day stay on Mars, the crew would carry out several 10-day rover traverses ranging up to 500 kilometers from the outpost (image at top of post).
After the first expedition, crews would no longer have at their disposal a pre-landed backup hab. The first manned Mars mission was expected to demonstrate hab reliability and landing safety, permitting NASA to do away with the backup hab and the heavy-lift rocket and TMI stage that would launch it.
If the lone hab lander crashed during landing, surviving crewmembers would use the MAV to evacuate to the orbiting ERV, where they would wait about 600 days for the beginning of the next minimum-energy Mars-Earth transfer opportunity. Similarly, in the unlikely event of a catastrophe that rendered the hab unlivable during the 600-day surface mission, surviving crewmembers could shelter temporarily in the pressurized rover, if it were available, then transfer to the MAV and evacuate to the ERV. There they would stay until the beginning of the next minimum-energy Mars-Earth transfer opportunity.
Assuming that the surface mission came off as planned, however, in October 2011 the first Mars crew would pack samples into the 2007 MAV and lift off. If the 2007 MAV failed pre-launch checks, the astronauts would drive their pressurized rover to the 2009 MAV. They would dock in Mars orbit with the 2007 ERV (or the 2009 ERV if the 2007 ERV were no longer operational), then would ignite the ERV's liquid oxygen/liquid methane TEI stage to leave Mars orbit. In the unlikely event that both MAVs or both ERVs failed, the 2009 crew could survive at their outpost until replacement payloads launched in early 2012 arrived at Mars in 2013.
As Earth grew large in their viewports, the first Mars explorers would enter the MAV capsule and undock from the ERV. They would then reenter Earth's atmosphere directly and descend to a landing using a steerable parachute. The ERV, meanwhile, would swing past Earth and enter solar orbit.
Assuming that the first crew did not need to use the 2009 MAV or ERV, the second Mars expedition crew would depart Earth in the first quarter of 2012, while the first crew was on its way home. In addition to the hab bearing the second crew, an ERV orbiter and a fuel factory/MAV lander would be launched during the 2012 Earth-Mars transfer opportunity for the 2015 third Mars expedition crew or to serve as backups for the 2012 crew. This pattern of launches could continue indefinitely, enabling intensive exploration of large areas of Mars.
Alternately - and this emerged as the MEST's preferred approach - at least three manned landings at a single site could build up a Mars base. The base approach would compensate for the lack of pre-landed backup hab landers after the first expedition; if a crew's hab became damaged during landing, they could transfer to the hab or habs already at the base site.
Multiple expeditions to a single site would also permit build-up of surface assets, potentially creating new Mars exploration capabilities. If all three expeditions occurred as planned, then by the time the third left Mars, the base would comprise four habs, three disused fuel factories lacking cargo or MAVs, three remotely placed reactors, and 120 tons of cargo including up to three pressurized and three unpressurized rovers.
"Mars Exploration Strategies: A Reference Program and Comparison of Alternative Architectures," AIAA 93-4212, David Weaver and Michael Duke; presented at the AIAA Space Program and Technologies Conference and Exhibit, September 21-23, 1993, Huntsville, Alabama.
Mars Exploration Study Workshop II, NASA CP-3243, Michael Duke and Nancy Anne Budden, editors, November 1993; report on a workshop "sponsored by NASA. . . Johnson Space Center and Held at NASA Ames, May 24-25, 1993."
http://beyondapollo.blogspot.com/2010/10/first-lunar-outpost-flight-plan-1992.html
http://beyondapollo.blogspot.com/2009/09/propellant-production-on-mars-1978.html
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