The Soyuz 11 crew are the only people to die in space

The three-man crew of Soyuz 11 died on June 30, 1971, when a valve jolted open about 80 miles (129 km) above Earth and emptied their capsule’s air in under a minute; it happened above the 100 km line, which makes them the only people ever to die in space itself. Georgi Dobrovolsky, Vladislav Volkov and Viktor Patsayev were heading home after a record 22-day stay aboard Salyut 1, the world’s first space station.

They were never meant to fly. The prime crew, Alexei Leonov, Valeri Kubasov and Pyotr Kolodin, was grounded three days before the June 6 launch when doctors saw a dark spot on Kubasov’s chest X-ray and feared tuberculosis. Rules required replacing the whole crew, so the backups flew. Kubasov’s diagnosis was later overturned.

What actually failed

Late on June 29, a warning light suggested the hatch to the descent module had not sealed. The crew cleaned the seals, the light stayed on, and controllers concluded the hatch was sealed. They were right; the hatch was never the problem.

The killer came during reentry, when explosive bolts fired to separate the Soyuz into its three sections. The shock jarred open a pressure-equalization valve designed to open only under the parachute, deep in the atmosphere. Evidence suggests the cosmonauts tried to close it by hand, a job that took minutes, but they lost consciousness and died within two minutes. They were not wearing pressure suits.

The capsule flew itself down to a normal landing in Kazakhstan; the only sign of trouble on the ground was silence on the radio. Recovery crews found all three still strapped in their seats. The Soviets halted crewed flights to redesign the Soyuz, and every cosmonaut since has worn a spacesuit during launch and landing.