The Perils of Zero Gravity

As imposing as the problems of extended space flight seem, most experts are confident that humans can survive the journey to Mars. But in what shape will they be when they get there? Says NASA Physicist Wendell Mendell: "It doesn't do you much good to deliver a human to the Martian surface if that human is inert for a time after landing."

Despite the experience gained from Apollo moon shots and the longer Skylab missions, U.S. doctors have some doubts about the ability of humans to withstand the effects not only of prolonged weightlessness but also of the transitions from gravity on earth (one G) to zero G in space to 0.38 G on Mars. "We're nowhere near ready to send a human to Mars," says Dr. Michael Bungo, director of NASA's Space Biomedical Research Institute at the Johnson Space Center. "We've got years more of basic research to do."

Soviet space doctors seem more sanguine. While no American has stayed in space for more than three months, the Soviets have repeatedly staged manned flights of longer duration, capped by the 326-day stay of Cosmonaut Yuri Romanenko last year aboard the orbiting space station Mir. "The experience of that flight," says Dr. Arkadi Ushakov of the Soviet Academy of Sciences, "testifies that we should be optimistic about long-duration space flight. Our knowledge in the field of weightlessness is growing, and we are learning what countermeasures need to be taken to ensure health and safety."

Ushakov believes that two effects of prolonged weightlessness, calcium loss in bones and muscle atrophy, can be largely prevented by exercise. A strict regimen on a treadmill helped keep Romanenko's muscle tone and reduced the calcium loss to a degree that Ushakov calls insignificant. But other effects attributed to weightlessness are still cause for concern. "There is a general weakening of the immune system in a long-duration flight," Ushakov says. "When this happens, there is a danger that every microorganism present in the ship can cause infection."

The Soviets have also detected changes in metabolic rates, which they say accelerate arteriosclerosis. Then there is the problem of neuromuscular control. Cosmonauts returning to earth after long flights have had trouble performing simple tasks like throwing a ball. Arriving on Mars, space travelers might be unable to carry out assignments.

The solution, many scientists believe, is to impart artificial gravity -- in the form of centrifugal force -- to the spacecraft. This might be accomplished by spinning a very large craft around its own axis. Other schemes envision three ships hooked together in a cartwheel-like arrangement that makes three revolutions per minute, or two vehicles attached by a half-mile-long tether rotating through space as the entire system speeds toward Mars. Still another idea is to schedule a daily workout for each crew member inside an on-board centrifuge, where resisting the centrifugal force would simulate working in gravity.

Apollo 11 Astronaut Michael Collins foresees some technical difficulties in such simulation. "Spinning wouldn't take that much power," he says. "But it still complicates things immeasurably from an engineering point of view." He notes that imparting spin to a Mars-bound craft could make both navigation and communication more difficult.

Space Scientist Carol Stoker, at NASA's Ames Research Center in California, points out that there would be benefits of artificial gravity beyond the physiological ones. "Toilets would flush properly, things wouldn't float in the air, and just think of surgery in zero gravity," she muses. Malcolm Cohen, chief of the neuroscience branch at Ames, worries about the possible physiological effects of rotation. "Weightlessness is the devil we know," he says, "and we have some idea how to overcome its effects. But artificial gravity in space is a devil we don't know well." Still, he concludes, "it's certainly an option we can't reject."