The large rocket engines for Apollo would be designed and tested at NASA's Marshall Space Flight Center in Huntsville, Alabama, where Wernher von Braun was director. When Lewis received its money for Mars work, Marshall was still a part of the Army Ballistic Missile Agency (ABMA), located at Redstone Arsenal.
Ernst Stuhlinger led advanced propulsion work at ABMA. He, like von Braun, was one of a few people who worked for both Adolf Hitler and Walt Disney. He spent World War II—with von Braun—designing and testing V-2 missiles at Peenemünde on the Baltic Sea. In 1945, the U.S. Army brought him to America along with dozens of his colleagues. In the late 1950s, Stuhlinger's ion-powered Mars armada starred in "Mars and Beyond," a Disney television episode.
Stuhlinger's ion drive used little propellant, cutting the number of expensive launches to assemble and fuel Mars vehicles. Because ion thrusters produce little acceleration, escaping Earth can take months. Once away from Earth, however, ion-powered spacecraft can eventually reach higher speeds than chemical- or nuclear-powered vessels. Stuhlinger's vehicles twirled to generate artificial gravity for their crews. Each ship's flat body was a radiator. Working fluid coursed through a nuclear reactor, which heated it; the reactor then drove a turbine to make electricity for ionizing—charging—and accelerating cesium propellant. The fluid passed through the radiator to cool down, then repeated the cycle.
Though NASA largely ignored ion drive, the Soviets based their Mars plans on it. The current NASA plan, which represents the work of numerous NASA centers, has a solar-powered ion "tug" boosting a chemical-fueled Mars vehicle to high-Earth departure orbit. This technique could cut the cost of a Mars expedition by half.
The EMPIRE Study: 1962-1964
According to author T.A. Heppenheimer, writing in NASA's newly published book The Space Shuttle Decision, von Braun realized that the Marshall center's role in Apollo would end as soon its large Saturn boosters were ready for moon flight. Unless NASA established some goal beyond Apollo, von Braun's center would face collapsing budgets and layoffs. Mars, some felt, might be the key to Marshall's future.
In mid-1962 Marshall launched the Early Manned Planetary Interplanetary Roundtrip Expeditions (EMPIRE) study. EMPIRE focused on Mars missions that could be made in the 1970s using modest extrapolation of Apollo technology. Mars landing missions were considered too ambitious, so the EMPIRE contractors—Lockheed, Ford Aeronutronic, and General Dynamics—were ordered to study easier manned Mars flyby and orbiter missions. However, Krafft Ehricke, director and principal author of the General Dynamics study, cheated—his EMPIRE Mars ships were good for both orbital and landing missions.
Ehricke, another Peenemünde veteran who later joined General Dynamics to help develop the Atlas missile, designed nuclear-powered EMPIRE spacecraft in two varieties—cargo and crew—intended to travel in convoys for safety. If a crew vehicle's engines became disabled, its crew module could move to a cargo vehicle so the expedition could be finished. The crew-carrying space craft tumbled end over end to create artificial gravity.
The General Dynamics scheme bears the unmistakable stamp of Ehricke. His study is immensely detailed—for example, it discusses such minutiae as in-flight exercise for the Mars crew—but a tad quirky. The in-flight exercise it recommends is table tennis.