On June 29, 1971, a Soviet space mission ended in tragedy when three Russian cosmonauts were found dead inside their spacecraft after returning to Earth. Inside the Soyuz 11 space capsule were cosmonauts Vladislav Nikolayevich, Viktor Ivanovich Patsayev, and Georgi Timofeyevich Dobrovolskiy. They were the only crew to ever board the world's first space station, Salyut 1. They launched on June 6, 1971 and spent 23 days doing science experiments aboard the space station before heading back to Earth. The reentry seemed to be going according to plan until the recovery team opened the capsule. Investigators believe the crew had become asphyxiated when a ventilation valve rattled open, causing the cabin to depressurize.