Progress 21 (Russian: Прогресс 21) was a Soviet uncrewed Progress cargo spacecraft, which was launched in May 1984 to resupply the Salyut 7 space station.

Progress 21 launched on 7 May 1984 from the Baikonur Cosmodrome in the Kazakh SSR.

[2][4] Progress 21 docked with the aft port of Salyut 7 on 10 May 1984 at 00:10 UTC, and was undocked on 26 May 1984 at 09:41 UTC.

[3][5] It remained in orbit until 26 May 1984, when it was deorbited.

[3][5] This article about one or more spacecraft of the Soviet Union is a stub.