Highly Elliptical Orbit (HEO) is an elliptic orbit with a high inclination and high eccentricity. This type of orbit results in the satellite spending the majority of its time over a specific area of the Earth, especially in the high-latitude regions. Here’s an overview of HEO satellites:

1. Applications:

  • Communication: Due to their unique orbit, HEO satellites can provide extended coverage to high-latitude areas where geostationary satellites might have limited visibility. This is particularly beneficial for regions near the poles.
  • Earth Observation: Satellites in HEO can monitor the polar regions more effectively than those in geostationary orbits. This is especially valuable for studying polar ice, weather patterns, and other environmental phenomena.
  • Navigation: Some navigation satellites use HEO to provide coverage in regions where traditional medium Earth orbit (MEO) navigation satellites might have limitations.

2. Advantages:

  • Extended Coverage: HEO satellites can provide continuous coverage for high-latitude regions, which might be challenging for satellites in other orbits.
  • Extended Observation Times: For Earth observation satellites, the slow movement of the satellite at the apogee (highest point) of its orbit allows for extended observation and data collection periods over specific areas.

3. Challenges:

  • Orbital Maintenance: Maintaining a satellite in a highly elliptical orbit can be more challenging than maintaining one in a circular orbit, requiring precise control and propulsion systems.
  • Varying Speed: The satellite’s speed varies significantly throughout its orbit, being slowest at apogee and fastest at perigee. This variation can pose challenges for certain applications and for maintaining a stable connection with ground stations.

4. Notable Examples:

  • The Molniya Orbit is a type of HEO that was popularized by the Soviet Union. Satellites in this orbit were primarily used to provide telecommunication services to the northern parts of Russia, where geostationary satellites had limited coverage.
  • Sirius XM, a satellite radio service in North America, originally used satellites in HEO to provide coverage.

5. Future of HEO:

With advancements in satellite technology and the rise of mega-constellations in low Earth orbit (LEO), the use of HEO for certain applications might decrease. However, for specific niche applications, especially those requiring extended coverage over high-latitude regions, HEO remains invaluable.