heo

High Earth Orbit (HEO) is an Earth-centered orbit in which the satellite’s apogee lies above the altitude of geostationary orbit (GEO), roughly beyond 35,786 kilometers (22,236 miles) above the Earth's equator. HEOs are typically highly elliptical, with a low perigee and a much higher apogee, which can result in a wide range of orbital periods. Because the apogee is well above GEO, ground coverage patterns differ markedly from those of low or medium Earth orbits.

A notable class of HEO is the Molniya-type orbit, characterized by an inclination near the critical value of about 63.4 degrees, a long orbital period of roughly 12 hours, apogee near 39,700 kilometers, and a perigee of a few hundred kilometers. This configuration yields prolonged dwelling times over high-latitude regions, giving improved visibility for northern communications and observation. Other HEO configurations include various long-arc elliptical orbits with apogees well above GEO, used for communications, reconnaissance, or specialized observation.

Uses and advantages of HEO include enhanced coverage of polar and high-latitude areas, allowing a single satellite to provide extended service over regions that are poorly served by geostationary systems. This makes HEO attractive for communications networks serving Russia, parts of North America, and other high-latitude regions. HEO can also support scientific and military missions requiring periodic high-latitude visibility.

Challenges of operating in HEO include exposure to radiation belts during perigee passes, greater orbital perturbations from Earth’s oblateness and third-body effects, and the need for ground stations capable of tracking highly eccentric, slow-moving ground tracks. Overall, HEO remains a specialized option for applications demanding long northern dwell times and polar visibility.