STS-41-B in the context of "Extravehicular activity"

An astronaut (from the Ancient Greek ἄστρον (astron), meaning 'star', and ναύτης (nautes), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member of a spacecraft. Although generally reserved for professional space travelers, the term is sometimes applied to anyone who travels into space, including scientists, politicians, journalists, and space tourists.

"Astronaut" technically applies to all human space travelers regardless of nationality. However, astronauts fielded by Russia or the Soviet Union are typically known instead as cosmonauts (from the Russian "kosmos" (космос), meaning "space", also borrowed from Greek κόσμος). Comparatively recent developments in crewed spaceflight made by China have led to the rise of the term taikonaut (from the Mandarin "tàikōng" (太空), meaning "space"), although its use is somewhat informal and its origin is unclear. In China, the People's Liberation Army Astronaut Corps astronauts and their foreign counterparts are all officially called hángtiānyuán (航天员, meaning "celestial navigator" or literally "heaven-sailing staff").

The Manned Maneuvering Unit (MMU) is an astronaut propulsion unit that was used by NASA on three Space Shuttle missions in 1984. The MMU allowed the astronauts to perform untethered extravehicular spacewalks at a distance from the shuttle. The MMU was used in practice to retrieve a pair of faulty communications satellites, Westar VI and Palapa B2. Following the third mission the unit was retired from use. A smaller successor, the Simplified Aid For EVA Rescue (SAFER), was first flown in 1994; it is intended for emergency use only.