Liquid methane/liquid oxygen constituted a good compromise, they found, because it yields 80 percent of hydrogen/oxygen's thrust, yet methane remains liquid at higher temperatures, and thus is easier to store. The Martian propellant factory would manufacture methane using a chemical reaction discovered in 1897 by French chemist Paul Sabatier. In the Sabatier reaction, carbon dioxide is combined with hydrogen in the presence of a nickel or ruthenium catalyst to produce water and methane. The manufacture of methane and oxygen on Mars would begin with electrolysis of Martian water. The resultant oxygen would be stored and the hydrogen reacted with carbon dioxide from Mars' atmosphere using the Sabatier process. The methane would be stored and the water electrolyzed to continue the propellant production process.
Ash, Dowler, and Varsi estimated that launching a one-kilogram sample of Martian soil direct to Earth would need 3.8 metric tons of methane/oxygen, while launching a piloted ascent vehicle into Mars orbit would need 13.9 metric tons. These are large quantities of propellant, so conjunction-class trajectories with Mars surface stay-times of at least 400 days would be necessary to provide enough time for propellant manufacture.
Benton Clark, with Martin Marietta (Viking's prime contractor) in Denver, published the first papers exploring the life-support implications of the Viking results. His 1978 paper entitled "The Viking Results—The Case for Man on Mars" pointed out that every kilogram of food, water, or oxygen that had to be shipped from Earth meant that a kilogram of science equipment, shelter structure, or ascent rocket propellant could not be sent. 14 Clark estimated that supplies for a 10-person, 1,000-day conjunction-class Mars expedition would weigh 58 metric tons, or about "one hundred times the mass of the crew-members themselves." The expedition could, however, reduce supply weight, thereby either reducing spacecraft weight or increasing weight available for other items, by extracting water from Martian dirt and splitting oxygen from Martian atmospheric carbon dioxide during its 400-day Mars surface stay.
Clark wrote that Mars offered many other ISRU possibilities, but that they probably could not be exploited until a long-term Mars base was established. This was because they required structures, processing equipment, or quantities of power unlikely to be available to early expeditions. Crop growth using the "extremely salty" Martian soil, for example, would probably have to await availability of equipment for "pre-processing . . . to eliminate toxic components." 15
The Vikings' robotic scoops barely scratched the Martian surface, yet they found useful materials such as silicon, calcium, chlorine, iron, and titanium. Clark pointed out that these could supply a Mars base with cement, glass, metals, halides, and sulfuric acid. Carbon from atmospheric carbon dioxide could serve clever Martians as a foundation for building organic compounds, the basis of plastics, paper, and elastomers. Hydrogen peroxide made from water could serve as powerful fuel for rockets, rovers, and powered equipment such as drills.
During the 1980s, the Mars ISRU concept generated papers by many authors, as well as initial experimentation. 16 Robert Ash, for example, developed experimental Mars ISRU hardware at Old Dominion University with modest funding support from NASA Langley 17 and from a non-government space advocacy group, The Planetary Society. 18 That a private organization would fund such work was significant.
Before ISRU could make a major impact, piloted Mars mission planning had to awaken more fully from its decade-long post-Apollo slumber. Post-Apollo Mars planning occurred initially outside official NASA auspices. This constituted a sea-change in Mars planning—up to the 1970s, virtually all Mars planning was government-originated. In the 1980s, as will be seen in the coming chapters, individuals and organizations outside the government took on a central, shaping role.
Chapter 7: The Case for Mars
We didn't know all of the people who finally did speak . . . until they called us! Somehow they heard about the conference, through the flyers we sent around and from word of mouth, and they volunteered. It really was a Mars Underground! (Christopher McKay, 1981) 1
Columbia
Columbia, the first Space Shuttle, lifted off from Pad 39A at Kennedy Space Center on 12 April 1981, with Commander John Young and Pilot Robert Crippen on board for a two-day test flight. Nearly 12 years before, the Apollo 11 CSM Columbia had left the same pad atop a Saturn V at the start of the first Moon landing mission. For Shuttle flights, the twin Complex 39 pads were trimmed back and heavily modified. Designated STS-1, it was the first U.S. piloted space flight since the joint United States-Soviet Apollo-Soyuz mission in July 1975.
The payload bay was the orbiter's raison d'être. Maximum payload to low-Earth orbit was about 30 metric tons, though center of gravity and landing weight constraints restricted this to some degree. The payload bay could carry satellites for release into orbit or a European-built pressurized laboratory module called Spacelab. The Space Shuttle orbiter was also the only space vehicle that could rendezvous with a satellite and capture it for repair or return to Earth—it could return about 15 metric tons to Earth in its payload bay. NASA hoped to use the Space Shuttle to launch components for an Earth-orbiting space station and other vehicles, such as aerobraking Orbital Transfer Vehicles (OTVs) based at the station.
At launch, the 2,050-metric-ton Shuttle "stack" consisted of the delta-winged orbiter Columbia and twin 45.4-meter-long Solid Rocket Boosters (SRBs) attached to a 47.4-meter-long expendable External Tank (ET). Columbia measured 37.2 meters long with a wingspan of 23.8 meters. Seconds before planned liftoff, the three Space Shuttle Main Engines (SSMEs) in the orbiter's tail ignited in rapid sequence, drawing liquid hydrogen and liquid oxygen propellants from the ET. Then, at T-0, the two SRBs lit up. Unlike the Saturn V, which climbed slowly during first-stage operation, Columbia leapt from the launch pad. Also unlike the Saturn V engines, the SRBs could not be turned off once they ignited, making abort impossible until they exhausted their propellants and separated. This was not considered a major risk—SRBs, used since the 1950s, were considered a mature technology.
Two minutes into STS-1, the SRBs separated and fell into the Atlantic for recovery and reuse. Columbia's SSMEs, the world's first reusable large rocket engines, continued pushing the orbiter and ET toward space. Eight and one-half minutes after launch, the SSMEs shut down and the ET separated. Young and Crippen fired Columbia's twin Orbiter Maneuvering System (OMS) engines to complete orbital insertion while the ET tumbled and reentered, then opened the long doors covering Columbia's 18.3-meter by 4.6-meter payload bay.
On 14 April Young and Crippen fired Columbia's OMS engines for about two minutes to begin reentry. The STS-1 reentry had almost nothing in common with previous piloted reentries. Columbia's heat shield did not ablate—that is, burn away—to protect it from the friction heat of reentry. Instead, in the interest of reusability, Columbia relied on more than 24,000 individually milled spun-glass tiles to shield its aluminum skin.
After a pair of close-timed sonic booms—they would become a Space Shuttle trademark—Columbia glided to a touchdown on the wide dry lake bed at Edwards Air Force Base, California. Future landings would occur on a runway seven kilometers from the Complex 39 Shuttle pads at KSC. 2
NASA heralded the flight as the start of a new era of routine, inexpensive space access that might spawn industry off Earth. An ebullient Young told reporters, "We're not really too far—the human race isn't—from going to the stars." 3
The Case for Mars
The Mars buffs who were gathered in Boulder, Colorado, for the first Case for Mars conference, just two weeks after the first Shuttle flight, would have settled for NASA's setting its sights on Mars—never mind the stars. Fueled by the Viking discoveries, would-be Mars explorers dared look beyond the Space Shuttle. They hoped that Mars ship propellants and components might soon be manifested as Shuttle payloads. They also saw in the Shuttle and in the Space Station Program (expected soon to follow) sources of hardware for Mars ship parts, much as planners in the 1960s envisioned using Apollo hardware for piloted Mars flybys.
The 1981 Case for Mars conference provided the first public forum for Mars planning since the 1960s. The conference crystallized around an informal seminar based on NASA's 1976 study The Habitability of Mars, organized by Christopher McKay, a University of Colorado at Boulder astro-geophysics Ph.D. candidate. The seminar brought together Mars enthusiasts from Boulder and around the country. The "Mars Underground," as they light-heartedly called themselves, decided in the spring of 1980 that the time was ripe for a conference on Mars exploration. 4
The Case for Mars conference drew its name from the title of Benton Clark's 1978 Mars ISRU paper (see chapter 6). Clark took part in the conference, along with about 300 other engineers, scientists, and enthusiasts. 5 It was the largest gathering of would-be Mars explorers since the 1963 Symposium on the Manned Exploration of Mars.
The conference was in part a brain-storming session—an opportunity to take stock of ideas on how to explore Mars. Among the concepts presented was S. Fred Singer's "PH-D Proposal," which drew upon Shuttle-related technology expected to exist in 1990. 6 Singer's scenario had staying power—he was still writing about it in the spring of 2000. 7
Singer's $10-billion expedition would use Deimos, Mars' outer moon, as a base of operations for exploring the Martian system. It was similar to the 1960s piloted flyby and orbiter missions in how it minimized spacecraft weight. None of the six to eight astronauts would land on Mars, though a sample-return lander would bring up a "grab sample" from the planet and two astronauts would visit Phobos, Mars' inner moon. The astronauts would remote-control between 10 and 20 Mars surface rovers during their two-to-six-month stay in the Martian system. At Deimos' orbital distance, round-trip radio travel time would be only one-fifth of a second.
Two astronauts would be "medical scientists" who would study human reactions to weightlessness, radiation, and isolation throughout the expedition. They would minimize risk to the crew from these long-duration space flight hazards by continually monitoring their health; data they gathered would also minimize risk for future Mars landing expeditions.
Singer's expedition would rely on solar-electric thrusters, using electricity from a large solar array to ionize and electrostatically expel argon gas. As described in chapter 2, electric propulsion thrusters produce constant low-thrust acceleration while using very little propellant. Singer assumed that the solar array would be available in high-Earth orbit in 1990 as part of a pre-existing Shuttle-launched cislunar infrastructure. The cost of the solar array was thus not included in Singer's expedition cost estimate.
At the start of the PH-D Proposal expedition, the unpiloted solar-electric propulsion system would spiral out from Earth, slowly gaining speed. Several weeks later, as it was about to escape Earth orbit, the piloted Phobos-Deimos craft would catch up, using chemical rockets, and dock. This technique minimized risk to crew by reducing the amount of time they had to spend in weightlessness and by speeding them through the Van Allen Radiation Belts. The solar-electric propulsion system would accelerate the spacecraft until expedition mid-point; then its thrusters would be turned to point in the direction of travel. The spacecraft would then decelerate until it was captured into orbit by Mars' gravity.
The 1990-91 target launch date would allow Singer's expedition to take advantage of a Venus flyby opportunity to gain speed and change course without using propellant. Total expedition duration would be "something less than two years." Electric propulsion plus Venus flyby plus postponing the piloted Mars landing until a later expedition would reduce spacecraft weight at Earth-orbit departure to about 300 tons.