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Updated answer: Mayak (Lighthouse/beacon) or URS truss, mounted on Salyut-7 in May 1986. Unfortunately, it is not the Sofora Arm, but the predecessor to it. From EVA's carried out from May 28 1986 to May 31 1986, Cosmonauts Leonid Kizim and Vladimir Soloviyov installed the URS (also known as Ma...