June 1971 -- Three Soviet cosmonauts die during re-entry after 24 days in an orbiting space laboratory, a record endurance flight at that time.
This one was described in the book
Set Phasers on Stun: And Other True Tales of Design, Technology, and Human Error by Steven M. Casey. That is one of the scariest books I\'ve ever read. It describes dozens of cases where poorly designed human/machine interfaces resulted in horrific loss of life. As I recall, the cosmonauts experienced a loss of atmosphere in their capsule on reentry. They could have tightened the hatch the air was escaping from, but the threading on the wheel that tightened the hatch required so many revolutions that it could never be closed within the time that a human could remain conscious without oxygen. Just a simple and incredibly stupid design flaw that no one considered.
