Salyut 3

Salyut 3, also known as OPS-2 or Almaz 2, was a Soviet space station launched on 25 June 1974. It was the second Almaz military space station and the first of that kind to be launched successfully, and it was included in the Salyut program to disguise its military nature. Because of that purpose the Soviet Union released little information about its design or its missions. The station reached an initial altitude of 219 to 270 km, and NASA reported a final orbital altitude of 268 to 272 km. Of three intended crews, only one boarded and worked on the station, arriving on Soyuz 14. Soyuz 15 failed to dock, and the third planned mission was cancelled. Several sources report that it carried multiple Earth-observation cameras as well as an on-board gun. The station was deorbited and re-entered the atmosphere on 24 January 1975.