I.

Introduction

Astronaut, crew member on piloted spaceflights. The term astronaut comes from the Latin words astrum (“star”) and nauta (“mariner”) and is used mostly in English-speaking countries. Russians who go into space are called cosmonauts. French space travelers are called spationauts. The International Astronomical Federation defines space travel as beginning 100 km (62 mi) above Earth, so some airplane pilots are considered astronauts. See Space Exploration.

Piloted spaceflight is an important aspect of space exploration. Humans in space can retrieve and repair satellites that might be useless otherwise. Studies of the effects of space on the human body have provided important medical knowledge for humans on Earth. Astronauts can perform experiments in space that machines cannot. Current piloted spaceflight may help scientists develop ways to allow humans to survive in space longer, which will be necessary if humans ever visit or colonize other planets.

Astronauts came into being in the late 1950s, when both the United States and the former Union of Soviet Socialist Republics (USSR) began piloted spaceflight programs. Both countries chose military pilots as the first astronauts. No one really knew what astronauts would be required to perform or how they would be required to behave, but it made sense to choose people with proven flying abilities and reliability in dangerous environments. Also, some of the earliest spacecraft were based on the high-performance aircraft that these pilots were accustomed to flying. Modern astronauts include scientists, engineers, medical doctors, and educators, as well as pilots.