Kosmos 257 (Russian: Космос 257 meaning Cosmos 257), known before launch as DS-P1-Yu No.17, was a Soviet satellite which was used as a radar calibration target for tests of anti-ballistic missiles.

It was built by the Yuzhnoye Design Bureau, and launched in 1968 as part of the Dnepropetrovsk Sputnik programme.

[1] Kosmos 257 was launched from Site 133/1 at Plesetsk,[2] atop a Kosmos-2I 63SM carrier rocket.

The launch occurred on 3 December 1968 at 14:52:21 UTC, and resulted in Kosmos 257's successful deployment into low Earth orbit.

Kosmos 257 was operated in an orbit with a perigee of 261 kilometres (162 mi), an apogee of 396 kilometres (246 mi), 70.9 degrees of inclination, and an orbital period of 91.10 minutes.