Salyut 2 (OPS-1)(Russian: Салют-2; English: Salute 2) was launched April 4, 1973.
It was not really a part of the same program as the other Salyut space stations, instead being the highly classified prototype military space station Almaz.
It was given the designation Salyut 2 to conceal its true nature. Despite its successful launch, within two days the as-yet-unmanned Salyut 2 began losing pressure and its flight control failed; the cause of the failure was likely due to shrapnel piercing the station when the discarded Proton rocket upper stage that had placed it in orbit later exploded nearby.
On April 11, 1973, 11 days after launch, an unexplainable accident caused the two large solar panels to be torn loose from the space station cutting off all power to the space station.
Salyut 2 re-entered on May 28, 1973.