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Most of the individuals who have gone into space are highly trained astronauts and cosmonauts, the two designations having originated in the United States and the Soviet Union, respectively. (Both taikonaut and yuhangyuan have sometimes been used to describe the astronauts in China’s crewed space program.) Those governments interested in sending some of their citizens into space select candidates from many applicants on the basis of their backgrounds and physical and psychological characteristics. The candidates undergo rigorous training before being chosen for an initial spaceflight and then prepare in detail for each mission assigned. Training centres with specialized facilities exist in the United States, at NASA’s Johnson Space Center in Houston, Texas; in Russia, at the Yuri Gagarin Cosmonaut Training Centre (commonly called Star City), outside Moscow; in Germany, at ESA’s European Astronaut Centre in Cologne; in Japan, at JAXA’s Tsukuba Space Center, near Tokyo; and in China, at Space City, near Beijing.

Astronauts and cosmonauts who undertook multiple spaceflights traditionally fell into one of two categories. The first consisted of pilots, often with military backgrounds, who had extensive experience in flying high-performance aircraft. They were responsible for piloting space vehicles such as the space shuttle and Soyuz. The other category included scientists and engineers who are not necessarily pilots. They had primary responsibility for carrying out the scientific and engineering activities scheduled for a particular mission. They were known in the U. S. space program as mission specialists and in the Russian space program as flight engineers. With the development of long-duration space stations such as Mir and the ISS, the distinction between pilot and nonpilot astronauts and cosmonauts has become less clear, because all members of a space station crew carry out station operations and experiments.

A third category of individuals who have gone into space was called variously payload specialists or guest cosmonauts. These individuals include scientists and engineers who accompany their experiments into orbit; individuals selected to go into space for political reasons, such as members of the U. S. Congress or persons from countries allied with the Soviet Union or the United States; and a few nontechnical people—for example, the rare journalist or teacher or the private individual willing to pay substantial amounts of money for a spaceflight. These people are intensively trained for their particular flight but usually go into space only once. At some future time, the costs and risks of human spaceflight may become low enough to accommodate the business of space tourism, in which many people would be able to experience spaceflight. Until then, access to orbit will be restricted to a comparatively small number of people.