A high Earth orbit is a geocentric orbit with an altitude entirely above that of a geosynchronous orbit (35,786 kilometres (22,236 mi)).[1] The orbital periods of such orbits are greater than 24 hours, therefore satellites in such orbits have an apparent retrograde motion – that is, even if they are in a prograde orbit (90° > inclination ≥ 0°), their orbital velocity is lower than Earth's rotational speed, causing their ground track to move westward on Earth's surface.
Name | NSSDC id. | Launch date | Perigee | Apogee | Period | Inclination |
---|---|---|---|---|---|---|
Vela 1A[2][3] | 1963-039A | 1963-10-17 | 101,925 km | 116,528 km | 6,519 min | 37.8° |
IBEX | 2008-051A | 2008-10-19 | 61,941 km | 290,906 km | 12,963 min | 16.9° |