TANSEI 1 (MS-T1)

TANSEI 1 (MS-T1) is an active satellite operated by ISAS (Japan), launched on 1971-02-16 from Uchinoura Space Center, Japan on the MS-T1 launch. After more than 55 years in orbit, it is one of the longest-surviving objects in the space catalogue. It orbits in Low Earth Orbit (LEO) at altitudes between 981 km and 1,100 km with an inclination of 29.7°. It travels at approximately 26,401 km/h (7.33 km/s), completing one full orbit every 106 minutes — that’s roughly 13.59 orbits per day. At its current altitude, the estimated orbital lifetime before atmospheric re-entry is ~500–1,000 years. Orbital Radar tracks TANSEI 1 (MS-T1) in real time using the latest two-line element set (TLE) data, providing live position, altitude, speed and orbital path updated continuously.

TANSEI 1 (MS-T1) orbits at an average altitude of 1,041 km in the upper LEO band, where atmospheric drag is negligible and objects can persist for centuries to millennia. This altitude is used by broadband constellations like OneWeb and by scientific missions requiring stable orbits far from the densest debris bands. Within ±50 km of TANSEI 1 (MS-T1)’s average altitude, there are currently 322 active payloads and 681 tracked debris or rocket body fragments — notable neighbours include ONEWEB-0041. With an inclination of 29.7°, TANSEI 1 (MS-T1) passes over latitudes between 29.7°N and 29.7°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. Japan operates approximately 209 active satellites in total, of which 7 share a similar altitude band with TANSEI 1 (MS-T1).