SL-6 R/B(2)

SL-6 R/B(2) is a spent rocket body associated with Russia (CIS), launched on 1975-01-30 from Plesetsk Cosmodrome, Russia on the Oko launch. After more than 51 years in orbit, it is one of the longest-surviving objects in the space catalogue. It orbits in Medium Earth Orbit (MEO) at altitudes between 6,407 km and 33,906 km with an inclination of 68.9°. It travels at approximately 13,955 km/h (3.88 km/s), completing one full orbit every 11 hours 57 minutes — that’s roughly 2.01 orbits per day. Its orbital eccentricity of 0.5183 gives it a noticeably elliptical path, with significant altitude variation between perigee and apogee. Spent rocket bodies like SL-6 R/B(2) are among the largest pieces of uncontrolled space debris and are priority targets for collision avoidance manoeuvres and future active debris removal efforts.

SL-6 R/B(2) orbits at an average altitude of 20,157 km in Medium Earth Orbit, the region between LEO and GEO (2,000–35,786 km). MEO’s higher altitude gives each satellite a much larger ground footprint than LEO, meaning fewer spacecraft are needed for global coverage — but signal latency is higher and radiation from the Van Allen belts is a significant design constraint. Within ±50 km of SL-6 R/B(2)’s average altitude, there are currently 105 active payloads and 10 tracked debris or rocket body fragments. With an inclination of 68.9°, SL-6 R/B(2) passes over latitudes between 68.9°N and 68.9°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 1,537 active satellites in total, of which 57 share a similar altitude band with SL-6 R/B(2).