The first flight of the Almaz manned military space station. In January 1973 the first Almaz OPS was delivered to Baikonur. Launch and initial orbital checkout went according to plan. But before a crew could be launched the station depressurized. It was concluded that a short in electrical equipment started a fire in pressure vessel, leading to rupture of hull and depressurization. An alternate theory was that debris from an explosion of the third stage of Proton penetrated the hull. Control was lost on April 25, 1973, and the OPS cased operations on 29 April. Decayed May 28, 1973. Initial crew was to have been Popovich and Artyukhin.
Officially: Testing of improved design, on-board systems and equipment; conduct of scientific and technical research and experiments.

Almaz 0101-1 finally entered orbit under the cover name Salyut 2 on 3 April 1973. The first 12 days of operation were normal. Two orbital corrections were made, and the Agat camera and ASA-34 topographical/star camera were operated successfully. But before a crew could be launched the station was lost. At 12:30 Moscow time on 14 April the station moved out of tracking range. When it returned at 03:16 telemetry showed the station had de-pressurised. On 16 April at 09:12 radio communications with the station ceased.

At first the station loss was attributed to a short in electrical equipment started a fire in pressure vessel, leading to rupture of hull and de-pressurisation. This would be consistent with the fire in Salyut 1. But study of telemetry later showed that the cause was a hole in the nitrogen tank of the engine unit pressurisation system. This prevented operation of the low thrust stabilisation engines and elevated temperatures in the bay, causing loss of proper radio telemetry, de-pressurisation, and then loss of main engines. It was theorised that debris from an explosion of the third stage of the Proton booster may have penetrated the nitrogen tank. Officially it was reported that control was lost on April 25, 1973, and the OPS ceased operations on 29 April. Salyut 2 decayed from orbit and re-entered on 28 May 1973 in the Pacific Ocean 3000 km east of New Guinea..