Soyuz 13 launched on 18 December 1973, 11:55:00 UTC. It carried commander Pyotr Klimuk and flight engineer Valentin Lebedev into orbit. This mission was the second test flight of the modified Soyuz spacecraft. Crew spent 7 deays in orbit and carried out various astrophysical studies. They also obtained ultraviolet spectrograms of stars with the help of an Orion 2 Space Observatory onboard the spacecraft. Crew returned to Earth, landing on 26 December 1973, 08:50:35 UTC.