M-3H R/B

M-3H R/B is a spent rocket body associated with Japan, launched on 1978-09-16 from Uchinoura, Japan on the EXOS-B launch. With over 48 years in orbit, it has far exceeded many satellites’ design lifetimes. It orbits in Medium Earth Orbit (MEO) at altitudes between 248 km and 9,077 km with an inclination of 31.3°. It travels at approximately 21,638 km/h (6.01 km/s), completing one full orbit every 3 hours 12 minutes — that’s roughly 7.48 orbits per day. Its orbital eccentricity of 0.4001 gives it a noticeably elliptical path, with significant altitude variation between perigee and apogee. Spent rocket bodies like M-3H R/B are among the largest pieces of uncontrolled space debris and are priority targets for collision avoidance manoeuvres and future active debris removal efforts.

M-3H R/B orbits at an average altitude of 4,663 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 M-3H R/B’s average altitude, there are currently 0 active payloads and 3 tracked debris or rocket body fragments. This is a relatively sparse altitude band, containing less than 1% of all active satellites. With an inclination of 31.3°, M-3H R/B passes over latitudes between 31.3°N and 31.3°S, covering the tropical and temperate zones where most of the world’s population resides. Low-to-mid inclination orbits are efficient to reach from equatorial and mid-latitude launch sites. Japan operates approximately 190 active satellites in total.