SL-4 R/B

SL-4 R/B is a spent rocket body associated with Russia (CIS), launched on 2026-04-16 from PKMTR on the Unknown launch. As a relatively recent addition to the catalogue, its orbital elements are well-characterised. It orbits in Low Earth Orbit (LEO) at altitudes between 453 km and 541 km with an inclination of 98.3°. It travels at approximately 27,426 km/h (7.62 km/s), completing one full orbit every 95 minutes — that’s roughly 15.23 orbits per day. Its near-polar, sun-synchronous orbit means it passes over any given point on Earth at approximately the same local solar time, ideal for consistent Earth observation lighting conditions. At its current altitude, the estimated orbital lifetime before atmospheric re-entry is ~1–3 years. Spent rocket bodies like SL-4 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.

SL-4 R/B orbits at an average altitude of 497 km in a sun-synchronous orbit (SSO), a specialised subset of LEO where the orbital plane precesses to maintain a constant angle relative to the Sun. This provides consistent lighting conditions on every pass — essential for Earth observation, weather monitoring and environmental science. Within ±50 km of SL-4 R/B’s average altitude, there are currently 9,440 active payloads and 215 tracked debris or rocket body fragments — notable neighbours include STARLINK-1017, STARLINK-1039, STARLINK-1047. This makes it one of the more crowded altitude bands, containing roughly 53.6% of all active satellites. With an inclination of 98.3°, SL-4 R/B passes over latitudes between 98.3°N and 98.3°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. Russia (CIS) operates approximately 1,288 active satellites in total, of which 59 share a similar altitude band with SL-4 R/B.