Highly Elliptical Orbit (HEO)

In satellite communications, a highly elliptical orbit (HEO) is an Earth-centered elliptical orbit with a large eccentricity, such that the satellite’s perigee (closest point to the Earth) is much lower than its apogee (farthest point from the Earth). This results in long dwell times near apogee, during which the satellite appears to move slowly relative to the Earth’s surface and can provide extended coverage of a particular region. Consequently, HEOs are often selected to provide high-elevation-angle coverage of high-latitude regions that are poorly served by geostationary satellites.

Many operational HEOs employ orbital periods of 12 or 24 hours and inclinations chosen to minimize perturbations of the argument of perigee. Examples of highly elliptical orbits used for satellite communications include the Molniya orbit, the Tundra orbit, and proposed concepts such as the LOOPUS orbit.