| Kosmos 257 | |
| Mission Type: | ABM radar target |
| Cospar Id: | 1968-107A |
| Spacecraft Type: | DS-P1-Yu |
| Manufacturer: | Yuzhnoye |
| Launch Date: | UTC |
| Launch Rocket: | Kosmos-2I 63SM |
| Launch Site: | Plesetsk 133/1 |
| Orbit Reference: | Geocentric |
| Orbit Regime: | Low Earth |
| Orbit Inclination: | 70.9 degrees |
| Orbit Period: | 91.10 minutes |
| Apsis: | gee |
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] It had a mass of .[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.[3] Upon reaching orbit, it was assigned its Kosmos designation, and received the International Designator 1968-107A.
Kosmos 257 was operated in an orbit with a perigee of, an apogee of, 70.9 degrees of inclination, and an orbital period of 91.10 minutes.[1] It remained in orbit until it decayed and reentered the atmosphere on 5 March 1969.[4] It was the seventeenth of seventy nine DS-P1-Yu satellites to be launched,[1] and the sixteenth of seventy two to successfully reach orbit.[5]