4. The Soyuz 11 Tragedy
After a record 23 days aboard Salyut 1, cosmonauts Georgi Dobrovolsky, Vladislav Volkov, and Viktor Patsayev perished during re-entry when a pressure equalization valve opened prematurely, causing rapid cabin depressurization. The crew, not wearing pressure suits, suffocated within minutes. Their bodies were found still strapped into their seats, a haunting testament to the isolation and dangers of space travel. (nasa.gov)