Soyuz 11 was launched on June 6, and successfully docked with Salyut 1, the world’s first space station, the following day. The threeperson crew of Georgi Dobrovolski, Viktor Patsayev, and Vladislav Volkov spent 23 days conducting a series of experiments and medical tests, marking a significant step forward in the space program.

On June 29, Soyuz 11 undocked from Salyut 1 to return to Earth. The descent appeared to be proceeding normally until contact was abruptly lost after the service module was jettisoned during the final stages of reentry. Nevertheless recovery teams found the Soyuz 11 capsule on the ground after an automatic descent with no obvious outward damage, yet got no response from the crew inside.

Opening the hatch, they discovered all three cosmonauts dead, ‘with darkblue patches on their faces and trails of blood from their noses and ears.’ Subsequent investigations revealed that a cabin vent valve had accidentally opened and depressurised the capsule when the service module was jettisoned at an altitude of 168 km (104 mi). The location of the valve made it impossible to block before a fatal loss of pressure. Without adequate pressure suits the crew fell unconscious and suffered cardiac arrest in less than a minute.

The Soyuz 11 disaster prompted an immediate investigation to improve safety measures for future missions, although the exact cause of death was not released for almost two years. Nevertheless the lessons learned from the tragic deaths of Dobrovolski, Patsayev, and Volkov mean that, despite other missions by both the USSR and the USA experiencing fatal disasters within the Earth’s atmosphere, the crew of Soyuz 11 are the only humans to have ever died in space.