 Complete the following phrase:  Salyut 7 was last inhabited in 1986 by the crew of Soyuz T-15, who ferried equipment from Salyut 7 to the new Mir space station. Between 19 and 22 August 1986, engines on Kosmos 1686 boosted Salyut 7 to a record-high mean orbital altitude of 475 km to forestall reentry until 1994. Retrieval at a future date by a 