ASTRONAUT

person trained to pilot a spacecraft, operate any of its various systems, or conduct scientific experiments aboard such a craft during spaceflights. The term is commonly applied to those participating in U.S. space missions, as opposed to the designation cosmonaut used to refer to Soviet space travelers. The U.S. Department of Defense awards the rating of astronaut to any military test pilot who has flown jet aircraft at altitudes of 50 miles (80 km) or higher. Alan B. Shepard was the first U.S. astronaut to fly in space, undertaking a 15-minute suborbital flight in a Mercury spacecraft on May 5, 1961, less than a month after Soviet cosmonaut Yury A. Gagarin had made the first manned spaceflight (April 12). From 1959 to 1980 the National Aeronautics and Space Administration (NASA), which manages the U.S. astronaut program, selected a total of 127 astronauts in nine groups. The criteria for choosing astronauts were modified through the years. Most of the individuals selected for the first three groups, primarily those assigned to the Mercury, Gemini, and early Apollo missions, were military pilots. From the fourth group onward, many persons who had no previous flight experience but who had advanced degrees in scientific disciplines such as physics, chemistry, and the earth sciences were appointed. This was particularly true of those selected for the space shuttle project, which included the first six women chosen for astronaut training. Such individuals serve as mission specialists whose primary responsibility is to perform scientific tasks on space missions. Astronauts receive extensive training to prepare themselves both physically and psychologically for the rigours and complexities of a space mission. Although the training includes classroom study of varied technical subjects, much of it is conducted in computer-controlled simulators and full-size mock-ups of spacecraft. Some such devices are used to help astronauts become accustomed to living and working in the weightless environment of space by simulating conditions of zero gravity. Others enable astronauts to familiarize themselves with the control, communication, and life-support systems of any given spacecraft and to practice difficult flight operations. Mission specialists with no flight training are also required to spend a year learning to fly high-performance jet aircraft so that they acquire the basic skills needed for flight safety.