Soyuz 15

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Soyuz 15 was a Soviet space mission in August 1974 intended to visit the Salyut 3 space station and practice docking maneuvers. The two-astronaut crew, Gennady Sarafanov and Lev Dyomin, launched on 26 August 1974 from Baikonur in a Soyuz 7K-T/A9 spacecraft with the callsign Dunay (Danube).

The spacecraft arrived at Salyut 3 but could not dock because the Igla docking system’s electronics malfunctioned. With not enough propellant for multiple docking attempts, the crew could not complete the link-up. They powered down nonessential systems and waited until the next day to re-enter. The mission lasted about 2 days and 12 minutes, with 32 orbits completed, and the crew landed on 28 August 1974, about 48 km southwest of Tselinograd.

Observers estimated the planned flight window was 19 to 29 days, but the failure ended the mission early. Official statements said the flight was to practice docking maneuvers with Salyut 3 and to test a new automatic docking system for future missions. The incident highlighted several design problems with the Soyuz 7K-T spacecraft, notably insufficient reserve propellant and electrical power for repeated docking attempts, and a docking system that needed significant improvements. Since fixes could not be made before Salyut 3’s lifespan ended, the work had to wait for future space stations. The backup Soyuz 15 craft was later flown as Soyuz 20, despite being past its intended shelf life.