Anyone who travels in space is called an astronaut. The Russians call their space travelers cosmonauts. Most astronauts stay in space for only a few days, but some remain there for months in permanently crewed space stations.
On missions into orbit, a commander and pilot fly the spacecraft. Mission specialists make observations and carry out experiments, and, if necessary, they perform EXTRAVEHICULAR ACTIVITIES (EVAs).
Pilots and commanders have flight training in jet planes and flight simulators. Mission specialists rehearse mission procedures and experiments. They may train for EVA submerged in water tanks, where conditions are similar to the weightlessness of space.
Any work that astronauts perform outside a spacecraft is called extravehicular activity (EVA) or spacewalking. On EVA, astronauts wear protective spacesuits. Usually, they are attached to the spacecraft by a safety tether. Sometimes they move around freely, using a jet-propelled backpack, or MMU (manned maneuvering unit).
One major job for spacewalking astronauts is to help rescue and repair satellites. Some shuttle astronauts carry out regular in-orbit servicing on the Hubble Space Telescope, replacing faulty or outdated equipment. Astronauts may also carry out space construction work. Lengthy EVAs are helping to assemble the International Space Station (ISS) from parts ferried into orbit by other vehicles.