HEO

A highly elliptical orbit is an orbital path where one point (apogee) sits far from Earth while the other (perigee) dips close to the surface. The spacecraft spends the majority of its orbital period near apogee, loitering over a specific region, usually a polar area. This asymmetry makes HEO fundamentally different from circular or moderately elliptical paths, where dwell time spreads evenly around the globe.

HEO satellites are commonly deployed at inclinations between 60 and 90 degrees to maintain coverage over high northern or southern latitudes. A typical HEO might have perigee at 500 km altitude and apogee at 40,000 km or higher. Because the spacecraft moves slowly at apogee (where gravity's pull weakens), it can broadcast or observe a fixed region for many hours per pass. This makes HEO valuable for communications serving Arctic regions or polar observation, where geostationary coverage fails.

The orbit's name reflects its geometry, not its purpose. 'Elliptical' describes the shape; 'highly' indicates the pronounced difference between perigee and apogee distances. The term distinguishes it from medium elliptical orbits (MEO) used by navigation systems like GPS, where perigee and apogee are less extreme.

Maintenance crews track HEO spacecraft using predicted pass times and orbital elements. Because apogee remains fixed in inertial space (not relative to Earth's rotation), coverage windows shift slowly across the calendar. This predictability allows ground stations to schedule antenna tracking, power management, and payload operations well in advance. Orbital decay from atmospheric drag is negligible above perigee altitudes typical of HEO, but station-keeping maneuvers are required periodically to correct drift caused by solar pressure and gravitational perturbations.

Russian communications satellites historically used HEO to serve high-latitude regions where ground infrastructure was sparse. The orbit requires higher launch energy than low Earth orbit (LEO) but delivers extended dwell time without the station-keeping burden of geostationary (GEO) satellites. For aviation and maritime operators in polar regions, HEO satellite links provide periodic contact that LEO constellations augment and that GEO cannot reach.