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Astronauts, or astronauts, the full name of the astronauts, refer to those who fly in space or who have made space flights. The criteria for determining space flight are not completely uniform. In the United States, people who travel more than 80 kilometers above sea level are called astronauts. The space flight defined by the International Aviation Federation requires more than 100 kilometers. As of April 18, 2004, a total of 440 people were defined according to the United States, and a total of 27,082 crew days (crew-day, defined by the United States) were spent in space, sharing 98 crew days in space. . Under the definition of the International Air Transport Association, only 434 people are eligible. Astronauts entering space come from at least 32 countries.