SURVIVING IN SPACE
Motion sickness troubles more than two thirds of all astronauts upon reaching orbit, even veteran test pilots who have never been airsick. Though everyone recovers after a few days in space, body systems continue to change. Deprived(丧失) of gravity information, a confused brain creates visual illusions. Body fluids surge to chest and head. The heart enlarges slightly, as do other organs. Sensing too much fluid, the body begins to discharge it, including calcium, electrolytes(电解液) and blood plasma(血浆). The production of red blood cells decreases, rendering astronauts slightly anaemic(贫血的). With the loss of fluid, legs shrink. Spinal(脊骨的) discs expand, and so does the astronaut—who may gain five centimeters and suffer backache. Though the process may sound terrible, astronauts adjust to it, come to enjoy it and seem no worse for wear—at least for short missions such as space shuttle flights that last a week or two.
During longer flights, however, physiology enters an unknown realm. As director of Russia's Institute for Biomedical Problems from 1968 to 1988, Oleg Gazenko watched cosmonauts return from long flights unable to stand without fainting, needing to be carried from the spacecraft. "We are creatures of the Earth", Gazenko told me. "These changes are the price of a ticket to space".
Americans, returning from months-long flights on Mir, the Russian space station, also paid the price, suffering losses in weight, muscle mass and bone density. NASA geared up to see how—even if—humans would survive the most demanding of space ventures, a mission to Mars, which could last up to three years. "We don't even know if a broken bone will heal in space," said Daniel Goldin, NASA's administrator. To get answers in 1997 Goldin established the National Space Biomedical Research Institute(NSBRI), a panel of experts from a dozen leading universities and research institute. NSBRI will Study biomedical problems and by 2010 will present NASA with a "go" or "no go" recommendation on a Mars mission.
Jeffrey Sutton, leader of the medical systems team at the NSBRI, has treated the head trauma, wounds, kidney stones and heart rhythm irregularities that one could encounter on the way to Mars. On the spacecraft he envisions, Mars-bound in the year, say, 2018, there may lurk harmful bacteria or carbon monoxide. No problem. The deadly substances will be detected by smart sensors—microprocessors no bigger than a thumbnail—that wander at will through the spacecraft, communicating their finds to a computer that warns the crew.
To cope with infection, Sutton plans a factory to make drugs, even new ones, to cope with possible organisms on Mars. Miniature optical and ultrasound devices will image body and brain, while a small X-ray machine keeps track of any bone loss. Smart sensors embedded in clothing will monitor an astronaut's vital functions. The crew will be able to craft body parts, Sutton says, precisely tooled to an astronaut's personal anatomy and genome stored in computer memory. Re searchers are building artificial liver, bone and cartilage(软骨) tissue right now.
Lying in wait beyond the Earth's atmosphere, solar radiation poses additional problems. The sun flings billions of tons of electrically charged gas into space, relegating Earth's volcanic eruptions to mere hiccups. Nevertheless, NASA officials are confident the accurate monitoring will warn astronauts of such events, allowing the crew to take refuge in an area where polyethylene(聚乙烯) shielding will absorb the radiation.
A second kind of radiation, cosmic rays from the Milky Way or other galaxies, is a more serious threat—possessing too much energy, too much speed for shielding to be effective. "There's no way you can avoid them," says Francis Cxucinotta, manager of NASA's Johnson Space Centre. "They pass through tissue, striking cells and leaving them unstable, mutila

A. Y
B. N
C. NG