MOS 1A (MOMO 1)

MOS 1A (MOMO 1) is an active satellite operated by Japan, launched on 1987-02-19 from TNSTA. With over 39 years in orbit, it has far exceeded many satellites’ design lifetimes. It orbits in Low Earth Orbit (LEO) at altitudes between 877 km and 889 km with an inclination of 98.8°. It travels at approximately 26,686 km/h (7.41 km/s), completing one full orbit every 103 minutes — that’s roughly 14.03 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 ~100–500 years. Orbital Radar tracks MOS 1A (MOMO 1) in real time using the latest two-line element set (TLE) data, providing live position, altitude, speed and orbital path updated continuously.

MOS 1A (MOMO 1) orbits at an average altitude of 883 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 MOS 1A (MOMO 1)’s average altitude, there are currently 210 active payloads and 1,591 tracked debris or rocket body fragments. With an inclination of 98.8°, MOS 1A (MOMO 1) passes over latitudes between 98.8°N and 98.8°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. Japan operates approximately 189 active satellites in total, of which 2 share a similar altitude band with MOS 1A (MOMO 1).