In contrast to a flight on a shuttle or even a stint on the space station, a journey to Mars would most likely preclude sending a sick astronaut home for treatment. And if giving CPR is tricky on Earth, it's downright bizarre if the resuscitator is floating inside a spacecraft. Scientists have programmed a computerized dummy patient on which astronauts practice in-flight emergency care. They have tested—with good results, says Hal Doerr, head of medical operational support at the agency's space biomedical institute—a dummy on the KC-135 airplane that NASA uses to simulate weightlessness. The so-called vomit comet executes dives and climbs to negate gravity's effect for as many as 25 seconds at a time.
Ionizing radiation, emitted by the Sun and other celestial objects, can penetrate a spacecraft and wreak havoc with human cells, potentially increasing the risk of cancer. To be sure, no astronaut has developed cancer attributable to radiation exposure in space, but so far the flights have been limited to low-Earth orbit or a few brief jaunts to the Moon. Preventing damage caused by solar and cosmic radiation is years away, says Frank Sulzman, manager of the space radiation health project at the Johnson Space Center. Adding a radiation shield to a spacecraft could add billions to the cost, according to some estimates. Though scientists have developed guidelines for how much radiation astronauts can be exposed to in low-Earth orbit, where the planet's magnetic field blocks some radiation, they're still in the dark about safe levels of radiation in deeper space, where radiation levels are higher. Last year, NASA opened a new $34 million Space Radiation Laboratory at Brookhaven National Laboratory in Upton, New York, to test the effects of radiation on microorganisms, human cells in lab dishes, and lab rodents. The researchers want to know how cosmic radiation affects the central nervous system and at what levels radiation causes cellular damage that could lead to malignant growth. In a few years, Sulzman says, the agency will set new standards for radiation exposure on short-term missions to the Moon, but it will be a decade or so before they've done enough lab research to establish guidelines for a voyage to Mars.
Some scientists question whether enough can ever be done to make a Mars journey reasonably safe. "I think everybody knows that high-energy radiation is going to be a terribly serious problem," says Robert Park, a University of Maryland physicist and director of public information at the American Physical Society. Park has long argued that only robots are suited to explore space. Also, he believes that even medically trained astronauts will lack the technology as well as the experience with weightlessness to handle serious medical emergencies in space, which are bound to arise. "There's always a problem when dealing with human beings," he says. "If a robot develops a problem, it's a pity, but we send up another one and don't declare a national day of mourning."
Charles, of the biomedical astronautics group, says if the United States decides to send people to Mars and back, the nation may simply have to live with the reality that the voyage—among the most hazardous undertakings in history—could not possibly be fail-safe. "All the problems may never be solved," he says, adding: "At some point a responsible program official will have to sign his or her name on the dotted line and say, 'We acknowledge that there is a level of risk remaining and we accept it.'"