Soon after the Lewis researchers began their work, Congress and the Eisenhower administration began to work toward the creation of a U.S. national space agency in response to Soviet space challenges. President Dwight Eisenhower wanted a civilian agency to ensure that headline-grabbing space shots would not interfere with the serious business of testing missiles and launching reconnaissance satellites. Senator Clinton Anderson (Democrat-New Mexico) led a faction that wanted the Atomic Energy Commission (AEC) to run the space program, citing as justification its nuclear-thermal rocket experiments. Others supported expansion of NACA, the federal aeronautics research organization founded in 1915. On 29 July 1958, Eisenhower signed into law legislation creating the National Aeronautics and Space Administration (NASA) from NACA and various Department of Defense space organizations. 3
When NASA opened its doors on 1 October 1958, Lewis became a NASA Center. The Lewis researchers sought to justify and expand their advanced propulsion work. In April 1959—two years before any human ventured into Earth orbit—they testified to Congress about their work and solicited funding for a Mars expedition study in Fiscal Year (FY) 1960. Congress granted the request, making the Lewis study the first Mars expedition study conducted under NASA auspices. 4
The Lewis researchers sought to develop weight estimates for Mars ships using their advanced propulsion systems. For their nuclear-thermal rocket analysis, the Lewis researchers assumed a Mars mission profile that would, by the end of 1960s, come to be virtually the standard NASA model:
The mission begins with the vehicle system in an orbit about the Earth. Depending on the weight required for the mission, it can be inferred that the system has been delivered as a unit to orbit—or that it has been assembled in the orbit from its major constituents . . . the vehicle containing a crew of seven men is accelerated by a high-thrust nuclear rocket engine onto the transfer trajectory to Mars. Upon arrival at Mars, the vehicle is decelerated to establish an orbit about the planet ...a Mars Landing Vehicle containing two men descends to the Martian surface . . . . After a period of exploration these men take off from Mars using chemical-rocket power and effect a rendezvous with the orbit party. The . . . vehicle then accelerates onto the return trajectory; and, upon reaching Earth, an Earth Landing Vehicle separates and . . . decelerates to return the entire crew to the surface. 5
For analysis purposes, the Lewis researchers targeted the 1971 launch opportunity, when Mars' close proximity to Earth minimized the amount of energy (and thus propellant) needed to reach it. They cautioned, however, that "[t]his is not meant to imply that actual trips are contemplated for this period." 6 They opted for a 420-day round trip with a 40-day stay at Mars, and found that the optimum launch date was 19 May 1971.
As might be expected, fast Mars trips generally require more propellant (typically liquid hydrogen in the case of a nuclear rocket) than slow trips. The more propellant required, the greater the spacecraft's weight at Earth-orbit departure. Thus, longer missions appear preferable if weight minimization is the dominant consideration in a Mars mission plan. The Lewis team noted, however, that crew risk factors had to be considered in calculating spacecraft weight. These were hard to judge because much about conditions in interplanetary space and on Mars remained unknown. In particular, they cautioned that "[c]urrent knowledge of radiation hazards is still not completely satisfactory." 7
Explorer 1 and Explorer 3 (launched 26 March 1958) detected the Van Allen Radiation Belts surrounding Earth. Their discovery was the first glimpse of an unsuspected reef, rock, or shoal menacing navigators in the new ocean of space. It raised the profile of ionizing radiation as a possible threat to space travelers.
No longer were the thin-skinned personnel spheres of von Braun's 1950s Mars ships judged adequate. Von Braun had made little provision for limiting crew radiation exposure, though he had expressed the hope that "by the time an expedition from earth is ready to take off for Mars, perhaps in the mid-2000s . . . researchers will have perfected a drug which will enable men to endure radiation for comparatively long periods." 8
The Lewis team did not place its trust in pharmacology. For their study, they assumed the following ionizing radiation sources: the Van Allen belts at Earth and Mars (in reality, Mars lacks radiation belts), continuous cosmic ray bombardment, solar flares, and, of course, the ship's nuclear-thermal rocket engine. Their spacecraft crew compartment, an unshielded two-deck cylinder providing 50 square feet of floor space per crewmember ("between that provided for chief petty officers and commissioned officers on submarines"), contained a heavily shielded cylindrical "vault" at its center, into which the crew would retreat during passage through the Van Allen belts, nuclear rocket operation, and large solar flares. 9 Crewmembers would also sleep in the vault; this would reduce their cosmic ray exposure during approximately one-third of each day.
Not surprisingly, the weight of radiation shielding required depended on how much radiation exposure for the crew was allowed. If major solar flares could be avoided during the 420-day voyage and a total radiation dose of 100 Roentgen Equivalent Man (REM) were permissible, then 23.5 tons of shielding would suffice, the Lewis researchers found. If, however, one major flare could not be avoided, shielding weight jumped to 82 tons to keep the total dose below 100 REM. If only 50 REM were considered permissible and one major flare could not be avoided, shielding weight would become "enormous"—140 tons. 10 "These data," they wrote, served "to underscore . . . the importance of determining more precisely the nature and virulence of the radiation in space." 11
The Lewis researchers determined that "short trips are as, or more, economical, in terms of weight, than long-duration missions," even though they generally required more propellant, because long trips required more heavy shielding to keep the crew within the radiation dose limit. 12 They estimated that a nuclear-thermal spaceship for a 420-day round trip in 1971 with a maximum allowable total radiation dose of 100 REM would weigh 675 tons at Earth-orbit launch.
Twirling Ion Ships to Mars
Just as the creation of NASA was prompted by the Cold War clash between the United States and the Soviet Union, so was the goal that dominated NASA's first decade. On 12 April 1961, Soviet cosmonaut Yuri Gagarin became the first person to orbit Earth. His Vostok 1 spacecraft completed one circuit of the planet in about 90 minutes. Gagarin's flight was a blow to the new administration of President John F. Kennedy, who had narrowly defeated Eisenhower's Vice President, Richard M. Nixon, in the November 1960 elections. Gagarin's flight coincided with the embarrassing failure of a Central Intelligence Agency (CIA)-sponsored invasion of Cuba at the Bay of Pigs (17-19 April 1961). 13
The tide of Kennedy's political fortunes began to turn on 5 May 1961, when astronaut Alan Shepard rode the Freedom 7 Mercury capsule on a suborbital hop into the Atlantic Ocean. On 25 May 1961, Kennedy capitalized on this success to seize back the political high ground. Before a special Joint Session of Congress, he called for an American to land on Earth's Moon by the end of the 1960s.
NASA had unveiled a 10-year plan in February 1960 that called for a space station and circumlunar flight before 1970, and a lunar landing a few years later. The Agency believed that this constituted a logical program of experience-building steps. 14 Mars planners were torn over Kennedy's new timetable. On the one hand, it put Mars work on the back burner by making the Moon NASA's primary, overriding goal. On the other hand, it promised to make launch vehicles and experience needed for Mars available all the sooner. 15
Two contenders led the pack of Apollo lunar mission modes in mid-1961—Earth-Orbit Rendezvous (EOR) and Direct Ascent. Both stood to benefit piloted Mars missions. In EOR, two or three boosters launched Moon ship modules into Earth orbit. The modules docked; then the resultant ship flew to the Moon and landed. Mars planners knew that experience gained through Moon ship assembly could be applied to Mars ship assembly. In Direct Ascent, the spacecraft flew directly from Earth's surface to the lunar surface and back. This called for an enormous launch vehicle which could be used to reduce the number of launches needed to put Mars ship parts and propellants into orbit.
NASA's Marshall Space Flight Center in Huntsville, Alabama, was responsible for developing the rockets required for lunar flight. Marshall began as the ABMA's Guided Missile Development Division. In the 1950s, the von Braun rocket team had developed some of the first U.S. missiles, including the intermediate-range Redstone, the "Americanized" version of the V-2. A Redstone variant called Jupiter-C launched the Explorer 1 satellite.
Just as Saturn was next after Jupiter among the planets, the Saturn series of rockets was next after Jupiter-C. Saturn I and Saturn IB used a cluster of Redstone/Jupiter tanks in their first stages. The engineers in Huntsville envisioned yet larger rockets. NASA's 1960 master plan called for development of an enormous "post-Saturn" rocket called Nova. Either Saturn or Nova could be used to carry out an EOR Moon mission; Nova was required for Direct Ascent.
Marshall might have performed the first NASA Mars study, but when the Lewis advanced propulsion engineers testified to Congress in 1959, the Huntsville organization was still not a part of NASA. Ernst Stuhlinger's group within the ABMA Guided Missile Development Division had commenced work on electric propulsion in 1953 and considered Mars expeditions in its design process.
In electric propulsion, a thruster applies electricity to propellant (for example, cesium), converting its atoms into positive ions. That is, it knocks an electron off each cesium atom, giving it an electric charge. The thruster then electrostatically "grips" the cesium ions and "throws" them at high speed. Electric propulsion provides constant low-thrust acceleration while expending much less propellant than chemical or nuclear-thermal propulsion, consequently reducing spacecraft weight. Low thrust, however, means low acceleration.
Stuhlinger presented a paper in Austria in 1954 describing a solar-powered electric-propulsion spacecraft with dish-shaped solar concentrators. 16 Walt Disney had contacted von Braun after reading the Collier's articles; this contact led to three space flight television programs from 1955 to 1957. Disney's Mars and Beyond, which premiered on 4 December 1957, featured Stuhlinger's distinctive umbrella-shaped nuclear-electric Mars ships, not von Braun's sphere-and-girder chemical ships. 17
The U.S. Army, eager to retain its foothold in missilery, was loath to release the von Braun team to NASA as required by President Eisenhower. Army resistance prevented von Braun, Stuhlinger, and their colleagues from officially joining the new space agency until 1 July 1960. However, they had by then worked directly with NASA for some time—hence their input to NASA's February 1960 master plan. 18 Wernher von Braun became Marshall's first director, and Ernst Stuhlinger became director of Marshall's Research Projects Division.
Stuhlinger's 1962 piloted Mars mission design, targeted for launch in the early 1980s, would include five 150-meter long Mars ships of two types—"A" and "B"—each carrying three astronauts. 19 As in von Braun's The Mars Project, risk to crew was minimized through redundancy. The expedition could continue if as many as two ships were lost, provided they were not of the same type. One ship could return the entire 15-person expedition to Earth under crowded conditions.
The three "A" ships would carry one 70-ton Mars lander each. At Mars, an unpiloted cargo lander would detach; if it landed successfully, the explorers would land in the second lander. If the cargo lander failed, the second lander would become an unpiloted cargo lander, and the third lander would deliver the surface team. The lander crew would stay on Mars for 29 days. If the crew lander ascent stage failed to fire, the explorers could return to Mars orbit in the cargo lander ascent stage.