INDEX

INDEX is an active satellite operated by Institute of Space and Astronautical Science (ISAS)/Japan Aerospace Exploration Agency (JAXA) (Japan), launched on 2005-08-23 from Baikonur, Kazakhstan. With over 21 years in orbit, it has far exceeded many satellites’ design lifetimes. It orbits in Low Earth Orbit (LEO) at altitudes between 519 km and 548 km with an inclination of 98.0°. It travels at approximately 27,353 km/h (7.60 km/s), completing one full orbit every 95 minutes — that’s roughly 15.11 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. At its current altitude, the estimated orbital lifetime before atmospheric re-entry is ~3–10 years. Orbital Radar tracks INDEX in real time using the latest two-line element set (TLE) data, providing live position, altitude, speed and orbital path updated continuously.

INDEX orbits at an average altitude of 534 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 INDEX’s average altitude, there are currently 3,512 active payloads and 304 tracked debris or rocket body fragments — notable neighbours include STARLINK-1184, STARLINK-1276, STARLINK-1451. This makes it one of the more crowded altitude bands, containing roughly 20.2% of all active satellites. With an inclination of 98.0°, INDEX passes over latitudes between 98.0°N and 98.0°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 50 share a similar altitude band with INDEX.