Overview
- The descent module lost pressure on June 30, 1971 when a separation shock opened a pressure‑equalisation valve and the cabin air escaped in under a minute.
- Onboard telemetry and biomedical sensors recorded heart‑rate spikes, attempts to manually close the valve, and crew loss of consciousness within about 30 to 40 seconds.
- The three men were the backup crew who had replaced the prime team after a preflight medical X‑ray and had spent 24 days aboard Salyut 1, a then‑record mission duration.
- The spacecraft’s parachute deployed and the capsule made a soft landing roughly 320 miles east of Zhezkazgan where recovery teams found the cosmonauts dead and resuscitation attempts failed.
- The accident revealed a vulnerability in the explosive‑separation/valve sequence and led to a lasting safety change requiring cosmonauts to wear pressure suits for Soyuz launches and landings.