It was a 325-kilogram (717 lb) spacecraft, which was built by the Yuzhnoye Design Bureau, and was used as a radar calibration target for anti-ballistic missile tests.

[1] Kosmos 421 was successfully launched into low Earth orbit on 19 May 1971, with the rocket lifting-off at 10:20:00 UTC.

[2] The launch took place from Site 133/1 at the Plesetsk Cosmodrome,[3] and used a Kosmos-2I 63SM carrier rocket.

[5] It was operated in an orbit with a perigee of 266 kilometres (165 mi), an apogee of 445 kilometres (277 mi), 70.9 degrees of inclination, and an orbital period of 91.65 minutes.

[1][6] It remained in orbit until it decayed and reentered the atmosphere on 8 November 1971.