In the movies, spaceships have artificial gravity, because it’s a heck of a lot easier to film that way. Real-life astronauts aren’t so lucky. The men and women who inhabit the Mir space station spend months in weightlessness.
Sure, it’s a lot of fun–flying around, leaving objects hanging in mid-air–but inside those cosmonauts’ and astronauts’ bodies, things are happening that aren’t much fun at all.
Consider Dr. David Wolf, for example, 41, the U.S. astronaut who just returned from four months on Mir. He’s a trained, fit man who could run a six-minute mile before he left Earth. On his return, he could hardly walk.
That’s because nearly every system in the body is tied to and affected by the force of gravity. When that force is removed, those systems change, in ways that could spell serious problems for long-duration space flights.
The most worrisome problem is one we mostly associate with the elderly here on Earth: osteoporososis. When gravity is removed, the bones immediately began to lose calcium, which is absorbed into the body. (Bedridden people and paraplegics suffer the same problem. Paraplegics, for instance, lose 30 percent of their lower-body bone mass within six to nine months of losing the use of their legs.)
The minerals lost from the leg and hip bones aren’t excreted. Instead, it appears they migrate, primarily to the head. In bed-rest studies, the skulls of participants became 10 percent denser over just 30 days. The body, in other words, is just making better use of its resources: in space the legs are useless, so the body quits worrying about them and moves to better protect that most vital of organs, the brain.
On Earth we build bones by running, jumping and weightlifting–anything that loads them with more than the body’s normal weight. So far, engineers haven’t come up with an effective method of mimicking that kind of exercise in space. If they can’t, astronauts on long missions may have to begin taking bisphononates, drugs which block the reabsorbing of bones.
Bones aren’t the only thing that weakens in space. Muscles lose protein, size and strength. Exercise programs developed so far have been only partially successful in stopping this process, which is one reason returning astronauts feel so weak.
The cardiovascular system is affected, too. On Earth, gravity pulls blood to the lower body, away from the head. Special nerves called baroreceptors detect the difference in pressure and cause the body to redirect blood flow, ensuring the brain gets the oxygen and sugar it needs to operate. In space, the nerves don’t sense any pressure difference, interpret that as meaning the body is bloated, and tell the body to increase urination. Over time, they forget how to respond to gravity at all. As a result, when the astronaut returns to Earth and tries to stand, no extra blood is sent to the brain, and the astronaut feels faint.
Astronauts grow two to seven centimetres in space, because gravity is no longer squashing their spine. (You get taller while you sleep, too; sometimes enough that you have to readjust your car’s rear-view mirror in the morning.) May astronauts suffer excruciating lower-back pain as a result, due to stretched ligaments.
They may also suffer from anemia–the number of oxygen-carrying red blood cells may drop as much as a third. Hormonal activity changes. Many astronauts suffer from space sickness, probably because what their eyes tell them doesn’t match the messages from their confused inner ears. Back on earth, spatial orientation can suffer as the body re-adapts to gravity, which can cause astronauts to stagger (in NASA-speak, they suffer from “postural instability.”)
There’s more. The gut becomes less effective at absorbing food. The immune system suffers–possibly due to living in a closed environment, the space habitat itself, stress, or inhibition of white cell maturation. This could make astronauts more susceptible to disease on long space flights.
Sleep is disrupted. Biological rhythms change–body clocks get out of synch with those of ground control, which affects job performance. Even temperature regulation can get out of whack.
With the International Space Station set to begin construction this year, more and more astronauts will be spending extended periods in space. Understanding the physiological changes they go through is one of the top priorities of space scientists. If we ever want to voyage deeper into space, we have to learn how to counteract some of these effects.
Real astronauts, alas, can’t call for a simple script rewrite.
