HIPPARCOS

HIPPARCOS is an active satellite operated by ESA (European Space Agency), launched on 1989-08-08 from Guiana Space Centre, Kourou. With over 37 years in orbit, it has far exceeded many satellites’ design lifetimes. It orbits in Medium Earth Orbit (MEO) at altitudes between 493 km and 35,747 km with an inclination of 7.2°. It travels at approximately 14,523 km/h (4.03 km/s), completing one full orbit every 10 hours 36 minutes — that’s roughly 2.26 orbits per day. Its orbital eccentricity of 0.7197 gives it a noticeably elliptical path, with significant altitude variation between perigee and apogee. Orbital Radar tracks HIPPARCOS in real time using the latest two-line element set (TLE) data, providing live position, altitude, speed and orbital path updated continuously.

HIPPARCOS orbits at an average altitude of 18,120 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 HIPPARCOS’s average altitude, there are currently 2 active payloads and 21 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 7.2°, HIPPARCOS passes over latitudes between 7.2°N and 7.2°S, concentrating coverage over equatorial and near-equatorial regions. Low-inclination orbits maximise revisit rates over specific tropical zones. ESA (European Space Agency) operates approximately 93 active satellites in total.