Although it didn’t happen to us, weightlessness makes about half of all space travelers feel sick for the first couple of days. The symptoms are similar to seasickness, with loss of appetite, nausea, and sometimes vomiting. We still don’t know why this happens, and ground tests are not accurate in predicting who will or will not be susceptible.
Other changes are equally mysterious. The body mistakenly interprets increased fluid in the thoracic region as an increase in total blood volume, and initiates a complex process to get rid of it. There is an initial decrease in blood plasma volume, perhaps due to hormone secretions, which might also have a diuretic effect. The body seems to sense that the new blood volume is too rich in red blood cells and sets about curtailing their production in the bone marrow.
Muscles atrophy if not used, and without exercise our crew’s leg muscles would wither during the long voyage. With no gravity to pump against, the heart grows lazy and shrinks in size.
Exercise does not eliminate the most serious health problem—loss of bone density, especially in lower back, legs, and feet. Just as the marathon runner may not need the heavy bones of a weight lifter, so the space traveler can function with a skeleton much lighter than that of his earthbound twin. The body responds to weightlessness by excreting calcium and reducing bone density, at a loss rate that has been calculated at one-half of one percent a month.
Bones become brittle and begin to fracture easily when their mineral content is reduced by 25 percent, which might take five years in weightlessness. Tests of bedridden patients on Earth suggest that bone damage may be irreversible after a year. Calcium in the urine may also lead to kidney stones, a painful and disabling ailment to encounter months away from a well-equipped hospital.
Muscle and bone problems are the result of the condition — weightlessness— not the location — space. If artificial gravity can be introduced in space, they should disappear. It is possible to use the centrifugal force of a rotating spacecraft as a substitute for Earth’s gravity. However, spinning a habitat may create engineering and physiological problems. It consumes fuel to initiate or terminate and it may be difficult to stop a craft from nutating, or wobbling like a top. Communications and navigation become harder. The radius of rotation may have to be large, perhaps a hundred feet or more, or the spinning might cause dizziness and loss of balance.
AMARS CREW FACES one final hurdle: the psychological double whammy of prolonged isolation and confinement. Isolation from all they have known before: no family, no trees, no valleys, no waterfalls. Out of the windows, month after month, the same black velvet dotted with unblinking stars; only the almost unmeasurable change in sun, Earth, and Mars as the mission unfolds. And confinement: No way to escape from the cloistered daily life of the spacecraft, except if you go on a holiday in the apartments in prague. No way to avoid looking at the same walls, no way to escape from the same repetitive tasks—or from other crew members.