In NASA's dusty archives sit the remnants of a hidden space age, one whose ambition far exceeded that of the Apollo moon program. In the 1960s, NASA was eager to broaden its successes, and it began preparing—on paper, at least—for what it felt certain would be its next big step: a mission to Mars. To us, these plans, filed and half-forgotten, seem audacious enough to be the work of science fiction writers, yet the men who conceived them were conservative engineers.

Most proposed launching astronauts to Mars during the 1970s, soon after Apollo reached the moon. And most were only studies, intended to give engineers a grasp of the basic problems of Mars exploration rather than to map out an actual expedition. The detailed planning would start as soon as a president backed a Mars program.

That, of course, never happened. In the 1970s, NASA Mars studies went dormant as the agency marshalled its diminished resources to build the space shuttle. Near decade's end, Mars interest revived—outside NASA. The Planetary Society, a space advocacy group, sponsored the first major organized post-Apollo Mars study. Thereafter, privately funded enthusiasts continued to carry the torch. In 1981 the first "Case for Mars" conference, organized by students at the University of Colorado in Boulder, gave Mars planners their first public forum in a decade, and revealed the existence of a "Mars underground" of NASA scientists and engineers eager to look beyond the shuttle. (Five more "Case for Mars" studies followed until the Mars Society, which now conducts annual conferences, took over in 1996.)

Meanwhile, NASA briefly reentered the picture in the 1980s with several big but ineffectual reports that culminated in one proposal for a 30-year Mars program, part of the Space Exploration Initiative (SEI), a $250 to $500 billion program drawn up during the Reagan administration that drew little more than derision from Congress. It emerged at a time of record federal budge deficits and died quickly.

Still, sped along by the energy of the Mars underground and numerous Mars-minded societies and organizations, expedition planning has gained momentum in the last decade, both within NASA and without. Though NASA is not proposing a mission to Mars, engineers do know more about the planet and the effects of spaceflight on humans. SEI taught them that big programs don't sell anymore, so their plans are more realistic, less dependent on a national commitment to an Apollo-size program. Of the 1,000-plus manned Mars mission studies conducted by individuals, NASA, other government agencies, private companies, and educational institutions in the last 50 years, most of the ideas studied today were generated in the 1960s. Here we present six of NASA's most intriguing Mars planning efforts from that period—a time when slide rules ruled.

NASA's First Mars Expedition: 1961

In April 1959, engineers at NASA's Lewis Research Center in Cleveland astonished the Senate Committee on Aeronautical and Space Sciences by appealing for modest funds to study sending astronauts to Mars. NASA was but six months old. Project Mercury, the first U.S. piloted space project, was still two year from placing a human in space. But in fact, Lewis had begun research into propulsion for interplanetary journeys as early as 1957. The center studied advanced nuclear and ion propulsion systems, and saw Mars expedition planning as a natural extension of its work. Congress gave Lewis its money.

By the time Alan Shepard became the first American in space in May 1961, the center had laid out NASA's first Mars expedition plan. A report presented by Lewis engineers to the Institute of Aerospace Sciences in January 1960 described the plan: "The mission begins with the vehicle system in an orbit about the Earth...the vehicle is decelerated to establish an orbit about the planet...a Mars Landing Vehicle...descends to the Martian surface..." After a period of exploration, the lander launches and docks with the orbiting spacecraft, which then accelerates back to Earth. This remained the standard Mars blueprint until the early 1990s, when the agency began focusing on in-situ resource utilization, which allowed for lower departure masses and thus reduced the need for politically sensitive nuclear propulsion.

On May 25, 1961, President Kennedy set NASA's sights on the moon. Would-be Mars explorers saw it as a mixed blessing: On the one hand, many technologies needed for a piloted Mars flight could be developed along the way; on the other, concentrating on the moon might postpone serious Mars work.

Twirling Ion Ships to Mars: 1961