astronaut, crew member on a U.S. manned spaceflight mission; the Soviet term is cosmonaut. Candidates for manned spaceflight are carefully screened to meet the highest physical and mental standards, and they undergo rigorous training. The early astronauts had all previously been test pilots, but later astronauts have included scientists and physicians, journalists, and politicians. As far as is possible, all conditions to be encountered in space are simulated in ground training. Astronauts are trained to function effectively in cramped quarters while wearing restrictive spacesuits; they are accelerated in giant centrifuges to test their reactions to the inertial forces experienced during liftoff; they are prepared for the physiological disorientation they will experience in space arising from weightlessness; and they spend long periods in isolation chambers to test their psychological reactions to solitude. Using trainers and mock-ups of actual spacecraft, astronauts rehearse every maneuver from liftoff to recovery, and every conceivable malfunction and difficulty is anticipated and prepared for. In addition to flight training, astronauts are required to have thorough knowledge of all aspects of space science, such as celestial mechanics and rocketry. Concurrent with all other preparation, astronauts must maintain excellent physical condition. Manned spaceflight began on Apr. 8, 1961, when the Soviet cosmonaut Yuri Gagarin orbited the earth. Other prominent cosmonauts included Vladimir Komarov, commander of the first Voskhod spacecraft, Alexis Leonov, first man to walk in space, and Valentina Terechkova, first woman cosmonaut. Prominent American astronauts include Alan B. Shepard, Jr., who made a suborbital flight on May 5, 1961; John H. Glenn, Jr., who was the first American to orbit the earth; Neil A. Armstrong, Jr., Edwin E. Aldrin, Jr., and Michael Collins, the crew of the Apollo 11 spacecraft that first landed on the Moon in 1969; and Sally K. Ride, America's first female astronaut.
See T. Wolfe, The Right Stuff (1975); G. L. Burdett and G. A. Soffen, The Human Quest in Space (1987); M. Collins, Carrying Fire (1989).