TANSEI 3 (MS-T3)

TANSEI 3 (MS-T3) is an active satellite operated by ISAS (Japan), launched on 1977-02-19 from Uchinoura Space Center, Japan on the MS-T3 launch. With over 49 years in orbit, it has far exceeded many satellites’ design lifetimes. It orbits in Medium Earth Orbit (MEO) at altitudes between 794 km and 3,805 km with an inclination of 65.8°. It travels at approximately 24,409 km/h (6.78 km/s), completing one full orbit every 2 hours 14 minutes — that’s roughly 10.74 orbits per day. Its orbital eccentricity of 0.1736 gives it a noticeably elliptical path, with significant altitude variation between perigee and apogee. Orbital Radar tracks TANSEI 3 (MS-T3) in real time using the latest two-line element set (TLE) data, providing live position, altitude, speed and orbital path updated continuously.

TANSEI 3 (MS-T3) orbits at an average altitude of 2,300 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 TANSEI 3 (MS-T3)’s average altitude, there are currently 2 active payloads and 11 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 65.8°, TANSEI 3 (MS-T3) passes over latitudes between 65.8°N and 65.8°S, covering most populated land masses in both hemispheres. This mid-inclination band balances global coverage with efficient launch energy requirements. Japan operates approximately 209 active satellites in total, of which 2 share a similar altitude band with TANSEI 3 (MS-T3).