Georgi Dobrovolski

Georgi Timofeyevich Dobrovolski (born June 1, 1928 in Odessa, died June 30, 1971) was a Soviet cosmonaut who flew on the Soyuz 11 mission and had the unfortunate distinction of being part of the second crew to die during a space flight.

After a normal re-entry, the capsule was opened and the crew was found dead. It was discovered that a valve had opened just prior to leaving orbit that had allowed the capsule's atmosphere to vent away into space, suffocating the crew.