HEO (Highly Elliptical Orbit): Advantages and Disadvantages

This page explores the pros and cons of using a Highly Elliptical Orbit (HEO) for satellites.

Introduction to Earth Orbits

Different types of Earth orbits offer unique advantages and capabilities:

• LEO (Low Earth Orbit): Commonly used for communication, remote sensing, the International Space Station, and the Hubble Space Telescope.
• MEO (Medium Earth Orbit): Primarily used for navigation systems like GPS.
• GSO (Geosynchronous Orbit) & GEO (Geostationary Orbit): Ideal for telecommunications and Earth observation. GEO is a specific type of GSO.
• Polar Orbit & SSO (Sun-Synchronous Orbit): Within 30 degrees of Earth’s poles. Utilized for reconnaissance, weather tracking, atmospheric measurements, and long-term Earth observation.
• HEO (Highly Elliptical Orbit): Can support applications similar to both LEO and MEO satellites.

What is HEO (Highly Elliptical Orbit)?

HEO is an oblong orbit around the Earth, characterized by one end being much closer to Earth than the other. It’s also known as a Molniya orbit.

Characteristics of HEO:

• Altitude: Ranges from approximately 20,000 to 47,000 km.
• Orbital Period: Longer than 24 hours, causing satellites in this orbit to appear retrograde.

HEO satellites are used for communication, satellite radio, remote sensing, magnetosphere studies, and astronomical observations. Examples include Ellipso, Molniya, Archimedes, and Inmarsat satellites (e.g., GX10A and GX10B).

Advantages of HEO

• Medium Round-Trip Delay: Offers a balance in signal delay.
• Variable Path Loss: Path loss between the satellite and Earth varies significantly depending on the satellite’s position in its orbit (smaller on the closer side, larger on the far side).
• Variable Coverage Area: Coverage area varies with the satellite’s position (smaller on the closer side, larger on the far side).
• Reduced Atmospheric Drag: HEO satellites experience less atmospheric drag compared to LEO and MEO satellites.
• Service to High-Latitude Regions: Can provide services to high-latitude regions that geostationary orbits cannot reach.
• Longer Dwell Time: Offers extended dwell time over specific areas of the sky.

Disadvantages of HEO

• Complex Satellite Systems: HEO satellite systems are more complex than those in other orbits.
• High Propagation Delay: Can result in the highest propagation delay on one side of the Earth.
• Selective Area Coverage: Offers coverage to selected areas.
• Apparent Opposite Direction: Satellites in HEO appear to move in the opposite direction.
• Higher Cost: Manufacturing and launching HEO satellites is typically more expensive.