January 1999

Missionaries to Mars

Continued from page 1

By James Oberg

Mooning Over Mars

if humans are to make it to mars, however, it will take much more than excitement. The successful flights of astronauts to the moon and back during the Apollo program of 1968 to 1972 rank as some of the greatest historical achievements of human technology; engineers overcame challenges in dozens of fields, including propulsion, thermal protection, communications and navigation, in a coordinated fashion. But the technological challenge of a manned mission to Mars represents a different order of magnitude.

Consider the basic numbers. One three-man Apollo mission used a single Saturn-V booster that placed about 120,000 kilograms of spacecraft and propellant in a low "parking orbit" just beyond the edge of Earth's atmosphere. After another rocket firing and a three-day voyage, two of the crew landed on the moon and spent several days venturing out onto the surface to collect specimens, take photographs and deploy instruments. Total mission duration for one of the Apollo flights was 10 to 12 days.

For Mars, many of these figures would go up dramatically. Most mission strategies require assembling a vehicle in parking orbit out of several components launched separately, adding up to 400,000 to 500,000 kilograms. The outbound voyage would last six to 10 months, followed by a sojourn on the martian surface lasting more than a year; during that time, crew members would make hundreds of trips outside rather than the three or four that Apollo spacesuits, tortured by rough usage and abrasive lunar dust, barely completed. The full mission would take close to three years and the astronauts' exposure to medical hazards such as long-term weightlessness and cosmic rays would be 100 times higher than it was for the lunar missions.

So at first glance, a Mars mission seems as though it would be many times more difficult than the lunar landings, and consequently many times more expensive (in current dollars, Apollo cost about $80 billion). But in the view of experienced space planners and economists, space technology has already reached levels that would enable Mars missions at costs equal to or even less than those of the Apollo program (see "Cheap Seats?," right).