SJ-4

SJ-4 is an active satellite operated by China, launched on 1994-02-08 from Xichang, China. With over 32 years in orbit, it has far exceeded many satellites’ design lifetimes. It orbits in Medium Earth Orbit (MEO) at altitudes between 383 km and 17,220 km with an inclination of 29.1°. It travels at approximately 18,452 km/h (5.13 km/s), completing one full orbit every 5 hours 10 minutes — that’s roughly 4.64 orbits per day. Its orbital eccentricity of 0.5549 gives it a noticeably elliptical path, with significant altitude variation between perigee and apogee. Orbital Radar tracks SJ-4 in real time using the latest two-line element set (TLE) data, providing live position, altitude, speed and orbital path updated continuously.

SJ-4 orbits at an average altitude of 8,802 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 SJ-4’s average altitude, there are currently 1 active payload and 9 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 29.1°, SJ-4 passes over latitudes between 29.1°N and 29.1°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. China operates approximately 1,219 active satellites in total.