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How many astronauts have died?
Short answer
So far, four spaceflights have ended in deaths: Soyuz 1, with Vladimir Komarov (1967); Soyuz 11, with three cosmonauts (1971); the Challenger, with seven people on board (1986); and the Columbia, also with seven (2003). Added to these are deaths on the ground and during training, such as the Apollo 1 capsule fire.

Four crews that did not return
Soyuz 1 ended in 1967 with the capsule's crash, because the parachute system failed; only Vladimir Komarov was on board. In 1971, rescue teams found the three cosmonauts of Soyuz 11 dead inside their capsule: when the modules separated, a valve had opened that let the air escape. In 1986, the Challenger broke apart shortly after launch with seven people on board, and in 2003 the Columbia broke up during reentry, also with seven. In all four cases, the entire crew died.
Who counts as an astronaut
The total figure depends on the definition used. If only deaths that occurred in flight above 100 kilometers of altitude are counted, the figure stays at these four missions. If flights for which the United States awarded astronaut wings are included, Michael Adams enters the count, who died in 1967 crashing an X-15 after reaching an extreme altitude. If ground accidents are added as well, the list includes the Apollo 1 capsule fire, in which Grissom, White, and Chaffee died, and the chamber fire in which Valentin Bondarenko died.
The minutes in which it happens
Lives were also lost outside of missions from the astronaut corps: Yuri Gagarin died in 1968 during a training flight with a MiG-15, and other candidates died in air accidents. That is why different sources give different figures, without any of them necessarily being wrong: what matters is what is included in the count. The distribution of spaceflight accidents is striking: they occurred during launch, when modules separated, and during reentry, that is, in the few minutes in which an enormous amount of energy is released, and never during the calm phase of a flight.
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