THOR DELTA 1 R/B

THOR DELTA 1 R/B is a spent rocket body associated with United States, launched on 1981-10-06 from Vandenberg SFB, California on the Solar Mesosphere Explore launch. With over 45 years in orbit, it has far exceeded many satellites’ design lifetimes. It orbits in Medium Earth Orbit (MEO) at altitudes between 551 km and 2,633 km with an inclination of 99.9°. It travels at approximately 25,470 km/h (7.08 km/s), completing one full orbit every 118 minutes — that’s roughly 12.20 orbits per day. Its orbital eccentricity of 0.1307 gives it a noticeably elliptical path, with significant altitude variation between perigee and apogee. At its current altitude, the estimated orbital lifetime before atmospheric re-entry is thousands of years. Spent rocket bodies like THOR DELTA 1 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.

THOR DELTA 1 R/B orbits at an average altitude of 1,592 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 THOR DELTA 1 R/B’s average altitude, there are currently 34 active payloads and 217 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 99.9°, THOR DELTA 1 R/B passes over latitudes between 99.9°N and 99.9°S, providing near-global coverage including the polar regions. Polar and near-polar orbits are used for reconnaissance, weather monitoring and Earth-observation missions that need to image every part of the planet. United States operates approximately 12,413 active satellites in total.