COSMOS 521

COSMOS 521 is an active satellite operated by PKO (Russia (CIS)), launched on 1972-09-29 from Plesetsk Cosmodrome, Russia on the DS-P1-M No. 4 launch. After more than 54 years in orbit, it is one of the longest-surviving objects in the space catalogue. It orbits in Low Earth Orbit (LEO) at altitudes between 980 km and 1,001 km with an inclination of 65.8°. It travels at approximately 26,490 km/h (7.36 km/s), completing one full orbit every 105 minutes — that’s roughly 13.73 orbits per day. At its current altitude, the estimated orbital lifetime before atmospheric re-entry is ~100–500 years. Orbital Radar tracks COSMOS 521 in real time using the latest two-line element set (TLE) data, providing live position, altitude, speed and orbital path updated continuously.

COSMOS 521 orbits at an average altitude of 991 km in the upper LEO band, where atmospheric drag is negligible and objects can persist for centuries to millennia. This altitude is used by broadband constellations like OneWeb and by scientific missions requiring stable orbits far from the densest debris bands. Within ±50 km of COSMOS 521’s average altitude, there are currently 399 active payloads and 1,106 tracked debris or rocket body fragments. With an inclination of 65.8°, COSMOS 521 passes over latitudes between 65.8°N and 65.8°S, covering most populated land masses in both hemispheres. This mid-inclination band balances global coverage with efficient launch energy requirements. Russia (CIS) operates approximately 1,553 active satellites in total, of which 193 share a similar altitude band with COSMOS 521.