The Polyus spacecraft, also known as Polus, Skif-DM, or 17F19DM, was a prototype orbital weapons platform designed to defend against anti-satellite weapons with recoilless cannon. It had an FGB (the Russian acronym for Functional Cargo Block, similar to the Zarya FGB that was the first component of the International Space Station) space resupply tug, derived from a TKS spacecraft, attached to control its orbit. It was also equipped with a sensor blinding laser to confuse approaching weapons and could launch test targets to validate the fire control system.

Polyus was launched May 15, 1987, as part of the first flight of the Energia system.

According to Yuri Kornilov, Chief Designer of the Salyut Design Bureau, Mikhail Gorbachev shortly before Polyus\' launch visited the Baikonur Cosmodrome and expressly forbid the on-orbit testing of its capabilities. Kornilov claims that Gorbachev was worried that it would be possible for the west to view this activity as an attempt to create a weapon in space and that such an attempt would compromise the country\'s leaderships\' statements on the USSR’s peaceful intent.

For technical reasons, the payload was launched upside down. It was designed to separate from the Energia, rotate 180 degrees, then complete its boost to orbit. The Energia functioned perfectly, but after disconnecting from Energia, the Polyus spun a full 360 degrees instead of the planned 180 degrees. When the rocket fired, it slowed and fell into the south Pacific ocean.

Parts of the Polyus project hardware were re-used in Kvant-2, Kristall, Spektr and Priroda Mir modules, as well as in ISS Zarya FGB.

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