SSTL S1-4

SSTL S1-4 is an active satellite operated by Surrey Satellite Technology Ltd. (United Kingdom), launched on 2018-09-16 from SRI. It orbits in Low Earth Orbit (LEO) at altitudes between 578 km and 580 km with an inclination of 97.5°. It travels at approximately 27,263 km/h (7.57 km/s), completing one full orbit every 96 minutes — that’s roughly 14.96 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. Its near-circular orbit (eccentricity close to zero) means it maintains a very consistent altitude throughout each revolution. At its current altitude, the estimated orbital lifetime before atmospheric re-entry is ~3–10 years. Orbital Radar tracks SSTL S1-4 in real time using the latest two-line element set (TLE) data, providing live position, altitude, speed and orbital path updated continuously.

SSTL S1-4 orbits at an average altitude of 579 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 SSTL S1-4’s average altitude, there are currently 3,069 active payloads and 532 tracked debris or rocket body fragments — notable neighbours include ONEWEB-0050, STARLINK-2112, STARLINK-3005. This makes it one of the more crowded altitude bands, containing roughly 17.6% of all active satellites. With an inclination of 97.5°, SSTL S1-4 passes over latitudes between 97.5°N and 97.5°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 Kingdom operates approximately 720 active satellites in total, of which 17 share a similar altitude band with SSTL S1-4.