Highly elliptical orbit (HEO) is a satellite orbit that has an altitude of about 1,000 to 35,756 km above the earth’s surface. Satellites in HEO are used for communications, satellite radio, remote sensing, and astronomical observations.

A satellite in an HEO orbit takes around 12-24 hours to complete one orbit around the earth. A major feature of an HEO is its apogee and perigee points. HEOs have a low perigee (the point of orbit closest to the Earth) with an altitude of under 1,000 km and a high apogee (the point farthest from the earth) with an altitude of over 35,756 km. 

As the satellite approaches perigee, orbital velocity is at its maximum, and as the satellite approaches apogee, the orbital velocity decreases and is at its minimum. This indicates that the satellite spends more time in the Apogee, where it moves very slowly and can be in the view over its operational area most of the time. The Satellite will have maximum coverage of the Earth’s surface when it is at the apogee (the point farthest from the earth), and have minimum coverage when it is at perigee(the point of orbit closest to the Earth).

HEOs can be used to provide coverage over any point on the globe. As a result of this ability to provide coverage over high latitudes over a specific region, countries such as Russia which need coverage over polar and near-polar areas make significant use of highly elliptical orbits. With two satellites in any orbit, HEOs can provide continuous coverage. Their only main disadvantage is that the satellite's position from a point on the earth does not remain the same and hence requires multiple satellites perfectly timed in the same path for continuous coverage.