How many astronauts have died in space?

On 30 June 1971 the Soyuz 11 crew were returning from Salyut 1, the world's first space station, after more than three weeks aboard. As the descent module separated from the service module, a pressure-equalisation valve jolted open and the cabin air escaped in seconds. The three cosmonauts were not wearing pressure suits, because the Soyuz cabin of that period had no room for three suited crew. The capsule flew its automatic re-entry and landed normally; the recovery team opened the hatch and found the crew dead. Soyuz crews have worn Sokol pressure suits for launch and landing ever since.

Every other fatal mission ended within the atmosphere. Soyuz 1 killed Vladimir Komarov in April 1967 when its parachute system failed during descent. Challenger broke apart 73 seconds after liftoff in January 1986, killing seven. Columbia disintegrated during re-entry in February 2003, again with seven aboard, after damage to a wing leading edge let hot gas into the structure. Added to Soyuz 11, those losses come to eighteen people killed on spaceflight missions.

Other crews died without leaving the ground or without reaching space. The Apollo 1 astronauts were killed by a fire inside their sealed capsule during a launch rehearsal in January 1967; test pilots have died on high-altitude research flights; cosmonauts and astronauts have been lost in aircraft accidents during training. Those are normally listed apart from in-flight fatalities, which is why published totals differ depending on where the line is drawn.