What is an astronaut?

Having been in space is not enough: astronaut status is tied to training and a professional assignment. Those selected by NASA, ESA, Roscosmos, JAXA, the Canadian agency or the Chinese agency go through a basic training period of around two years that covers spacecraft systems, robotics, Russian or English depending on the program, survival training, diving in neutral-buoyancy pools to rehearse spacewalks, and flying jet aircraft. Only afterward do they receive the certification that makes them eligible for a crew assignment.

Within a mission there are different roles. The commander and pilot are responsible for the vehicle; mission specialists handle experiments, maintenance and spacewalks; and on Space Shuttle flights there was the role of payload specialist, reserved for scientists or representatives of an international partner with shorter training.

The three words denote the same profession in different linguistic traditions. "Cosmonaut" is the Russian term, inherited from the Soviet program that sent Yuri Gagarin into orbit in 1961. "Taikonaut" became popular in the Western press for Chinese crew members, although China officially uses *hangtianyuan*. France used the term "spationaute" for a time for its crew members.

A separate question is where space begins. The International Aeronautical Federation sets the boundary at 100 km altitude, the so-called Kármán line. The United States has historically recognized spaceflight from 80 km, a criterion applied both by X-15 pilots and, later, by the FAA for commercial flights. That difference explains why some crew members appear as astronauts on some lists and not on others.