During the last thirty years, a select group of men and women from several nations have journeyed into space. These astronauts have operated spacecraft and space stations. They have launched, repaired, and retrieved satellites and telescopes. Their jobs also include studying how being in space affects people and other living organisms. They do this by conducting scientific experiments in space.

American astronauts work for the National Aeronautics and Space Administration (NASA). They live and train at the Lyndon B. Johnson Space Center in Houston, Texas. NASA selects three types of astronauts: pilots, mission specialists, and payload specialists. The pilots command and fly the spacecraft. Mission specialists work with the astronaut pilots to maintain the spacecraft and its equipment. Payload specialists carry out scientific experiments on board the spacecraft.

Once in orbit, the astronauts experience a condition called microgravity. The spacecraft falls freely toward the earth, but this "fall" combines with the shuttle's forward speed to maintain the spacecraft's circular orbit. "Free fall" creates a condition of near weightlessness which has profound physical effects on space travelers. For example, many astronauts experience "space sickness" because in space, the balance organs of the inner ear have no way to tell up from down. Meanwhile, the astronauts' eyes report that their bodies are "floating" in air. These effects combine to make the astronauts feel nauseous.

These are just a few of the effects of microgravity on astronauts. It takes a lot of training and study to understand them and to be able to work around them. Scientists are now studying the brain's function in the environment of space to help us learn more about brain physiology in space and on Earth. In the meantime, many people dream of space travel. Are you one of them?