America at the Threshold
The SEI Synthesis Group released its report America at the Threshold in May 1991. 55 The report, though written at a time when U.S.-Soviet space cooperation was becoming increasingly important to NASA's future, contained little on cooperation. The Synthesis Group report was the last in the series of high-profile documents proposing future directions for NASA that had begun with the National Commission on Space report in 1986.
Stafford headed a group of 22 experts from NASA and the Departments of Energy, Defense, and Transportation. They included retired JSC director Christopher Kraft and retired JSC engineering director Maxime Faget. Robert Seamans, retired from top NASA, Air Force, and Department of Energy posts, was Stafford's co-chair. They set up shop with a staff of 40 in Crystal City, Virginia, just outside Washington, DC.
The SEI Outreach Program provided the Synthesis Group with about 500 inputs from the 44,000-member AIAA. The Aerospace Industries Association, meanwhile, organized corporate briefings. These included a presentation by Martin Marietta featuring the Mars Direct plan. NASA took out newspaper advertisements around the country and set up toll-free telephone numbers to receive ideas from the public. About 900 concepts were submitted to Rand Corporation by early September. The national laboratories turned over their ideas during September. All told, the Synthesis Group had about 2,000 inputs in hand in late September. 56
The Synthesis Group was to submit at least two concepts based on these inputs to Truly, who would forward them to the National Space Council. A two-year NASA study would follow, during which the Agency would attempt to identify critical technologies needed to carry out the concepts proposed by the Synthesis Group.
In June 1991, the Group distributed 40,000 copies of its colorful report, emblazoned with the U.S. Presidential Seal, to industry, educators, government agencies, and international organizations. The report outlined four SEI architectures. In all of them, the ultimate goal was landing Americans on Mars. The Moon would serve as a rehearsal stage; nuclear systems would push spacecraft and power bases; and heavy-lift rockets would blast everything into orbit. Including nuclear propulsion was, as in the 1960s, in part a concession to Los Alamos, which had begun stumping for SEI nuclear systems as early as February 1990. 57
In none of the architectures was Space Station Freedom an element of Mars transportation infrastructure. In September, Aviation Week & Space Technology quoted Stafford as saying, "I know when I went to the Moon . . . on Apollo 10, I did not have to stop at a space station." 58 This was a radical departure from SEI's ground rules. It was, in fact, a deviation from ground rules that had guided Mars planning since the time of the Apollo Moon missions, when NASA had first began to push for a space station.
Stafford's Architecture I emphasized Mars exploration but would spend five years on the Moon first. In 2005, a heavy-lift rocket would launch an automated cargo lander/habitat to the Moon. A second heavy-lift rocket would launch a crew of six to lunar orbit. Five astronauts would land on the Moon near the cargo lander; the sixth astronaut would mind the mothership in lunar orbit, just as the CM Pilot had minded his craft during Apollo Moon landing missions. The surface crew would stay on the Moon for 14 Earth days (one lunar daylight period).
In 2009-10, after four more heavy-lift rocket launches and two more lunar expeditions, a six-person Mars rehearsal crew would carry out a 300-day Mars expedition simulation in lunar orbit and on the Moon. After that, the Moon would not be visited again.
In 2012, the ninth heavy-lift rocket of Synthesis Group Architecture I would launch the first nuclear rocket of the program. It would push an automated cargo lander to Mars. The cargo lander would include a habitat identical to that landed on the Moon. The first six-person Mars crew would leave Earth in 2014 on the tenth heavy-lift rocket. After a flight lasting approximately 120 days, they would decelerate into Mars orbit using their nuclear-thermal rocket, separate from the Mars transfer habitat, and land near the 2012 cargo lander. The crew would spend 30 days testing systems and exploring before returning to the transfer spacecraft and firing the nuclear rocket for return to Earth. In the same launch opportunity, the eleventh heavy-lift rocket of the program would launch a cargo lander for the 2016 Mars expedition, which would spend 600 days on Mars. The report stated that Architecture I was conducive to more rapid execution (first Mars landing in 2008) if provided with "robust" funding.
The other architectures were generally similar. Architecture II, "science emphasis for the Moon and Mars," was designed to characterize the Moon and Mars scientifically through wide-ranging exploration and visits to multiple scientifically interesting landing sites. Architecture III, "Moon to stay and Mars exploration," emphasized a permanent lunar base. The base would achieve 18-person permanent staffing in 2007. A total of 47 six-person piloted expeditions would reach the Moon between 2004 and 2020, and the first piloted Mars landing would occur as in Architecture I.
The Stafford Group noted that "space is a unique store of resources: solar energy in unlimited amounts, materials in vast quantities from the Moon and Mars, gases from the Martian atmosphere, and the vacuum and zero gravity of space itself"—hence Architecture IV, which emphasized "space resource utilization." 59 Lunar ISRU would aim first for self-sufficiency; then it would export to Earth electricity and Helium-3 for fusion reactors. Mars ISRU would aim solely to provide self-sufficiency—the planet's greater distance would make exports to Earth impractical, the report stated. The Mars rehearsal on the Moon would take place as described in Architecture I, and Mars expeditions would occur in 2016 and 2018. The second expedition would establish an experimental greenhouse. Both expeditions would manufacture propellants for their rovers from Martian air.
The report made organizational recommendations for carrying out its program. It called upon NASA to establish "a long range strategic plan for the [N]ation's civil space program with the Space Exploration Initiative as its centerpiece," and asked President Bush to "establish a National Program Office by Executive order." In addition, it advocated advanced technology development programs. 60
The SEI Synthesis Group had produced a cut-price version of The 90-Day Study—a disappointing outcome, given the magnitude of the Outreach Program. Few Americans took notice of America at the Threshold, and few of its recommendations were implemented. SEI funding fared no better in FY 1992 and FY 1993 than in the previous two years. The planned two-year follow-up study of critical technologies did not take place.
NASA disbanded the Headquarters Exploration Office in late 1992. The JSC Exploration Directorate closed down a few months later. 61 The poorly attended Case for Mars V conference in May 1993 became SEI's wake. By the beginning of 1994, Mars planning across NASA threatened to slip back into its post-Apollo slumber.
Chapter 10: Design Reference Mission
Recent developments in the exploration of Mars have served to focus attention once again on the possibilities for human exploration of that planet. The unprecedented interest shown in the recently published evidence pointing to past life on Mars and in the Mars Pathfinder mission indicates that exploration of our solar system has not become so commonplace that the public cannot become surprised and fascinated by the discoveries being made. And these events have also rekindled the questions not of whether, but when will humans join the robots in exploring Mars. (Kent Joosten, Ryan Schaefer, and Stephen Hoffman, 1997) 1
Mars Direct
Like the STG, NCOS, and The 90-Day Study teams before it, the SEI Synthesis Group opted for a "brute-force" approach to piloted Mars exploration requiring such big-ticket items as heavy-lift rockets that dwarfed the old Saturn V, nuclear-thermal propulsion, and a lunar outpost. As has been seen, this approach has never gained much support. Proposing it repeatedly over the past 30 years has succeeded mainly in ingraining the belief that Mars exploration must be exorbitantly expensive (more expensive than a small war, for example) and needs decades to achieve its goal. Subsequent NASA Mars plans have sought to apply technologies new and old to reduce cost and tighten the schedule. They have begun the slow process of expunging the perception that a Mars mission must be conducted in a costly way.
Since 1992, NASA has based most of its Mars plans on the Mars Direct concept developed in 1990 by Martin Marietta. Mars Direct originated in Martin Marietta-sponsored efforts to develop SEI concepts. The plan has had staying power in part because it is an appealingly clever synthesis of concepts with respectable pedigrees. Mars Direct employs ISRU, aerobraking, a split mission architecture, a tether for artificial gravity, and a conjunction-class mission plan—all concepts that date from the 1960s or earlier. Mars Direct was influenced by the Case for Mars conferences, the Ride Report, and the NASA Exploration Office Studies, as well as ISRU research conducted by Robert Ash, Benton Clark, and others. 2
Mars Direct has also had staying power since 1990 because one of its authors, engineer Robert Zubrin, has remained its zealous champion. On April 20, 1990, Zubrin and co-author David Baker unveiled their plan to NASA engineers gathered at NASA Marshall. 3 Mars Direct went public at a National Space Society conference in Anaheim, California, in June 1990. It first received widespread attention a week later, after Zubrin presented it at the Case for Mars IV conference in Boulder, Colorado. 4
In August 1990 the AIAA magazine Aerospace America carried a non-technical description of Mars Direct capturing Zubrin's promotional style. 5 It asked,
Can the United States send humans to Mars during the present decade? Absolutely. We have developed vehicle designs and a mission architecture that can make this possible. Moreover, the plan we propose is not merely a "flags and footprints" one-shot expedition, but would put into place immediately an economical method of Earth-to-Mars transportation, vehicles for long-range surface exploration, and functional bases that could evolve into a mostly self-sufficient Mars settlement. 6
Zubrin and Baker had the first Mars Direct expedition beginning in December 1996 with the launch of a Shuttle-derived heavy-lift rocket from the Kennedy Space Center. The rocket, which Zubrin and Baker dubbed Ares, would consist of a modified Shuttle External Tank, two Advanced Solid Rocket Boosters, and four Space Shuttle Main Engines mounted on the External Tank's underside. A liquid hydrogen/liquid oxygen upper stage and an unpiloted Mars cargo lander covered by a streamlined shroud sat on top of the External Tank. The 40-ton cargo lander included an aerobraking heat shield, descent stage, Earth-Return Vehicle, In-Situ Resource Utilization propellant factory, 5.8 tons of liquid hydrogen feedstock for propellant manufacture, and a 100-kilowatt nuclear reactor on a robot truck. The lander was, they wrote, "light enough for the booster upper stage to project it directly onto a six-month transfer orbit to Mars without any refueling or assembly in Earth orbit"—hence the name Mars Direct. 7
The cargo lander would aerobrake in Mars' atmosphere and land. After touchdown, the robot truck bearing the reactor would trundle away to a natural depression or one created using explosives. It would lower the reactor into the crater—the crater rim would shield the landing site from radiation—then would run cables back to the lander. The reactor would activate, powering compressors which would draw in Martian air to manufacture propellant. Manufacturing propellants on Mars would help minimize the weight of propellants that had to be shipped from Earth.
The propellant factory would use the Sabatier process first proposed for use on Mars in 1978 by Robert Ash, William Dowler, and Giulio Varsi. Liquid hydrogen feedstock would be exposed to Martian carbon dioxide in the presence of a catalyst, producing 37.7 tons of methane and water. The methane would be stored and the water electrolyzed to yield oxygen and more hydrogen. The oxygen would then be stored and the hydrogen recycled to manufacture more water and methane. Additional oxygen would be manufactured by decomposing carbon dioxide into carbon monoxide and oxygen and venting the carbon monoxide. In a year, the propellant factory would manufacture 107 tons of methane and oxygen propellants. The piloted Mars spacecraft would not be launched until the automated cargo ship finished manufacturing the required propellants, thereby reducing risk to crew.