Medium Earth Orbit (MEO)

Medium Earth Orbit (MEO) is the orbital region that spans the altitude range between Low Earth Orbit (LEO) and Geostationary Earth Orbit (GEO). MEO occupies altitudes between LEO and GEO and is often analyzed in relation to the Van Allen radiation belts according to many definitions.

Orbital Altitude Velocity and Period

Medium Earth Orbit refers to a band of altitudes rather than a single fixed altitude. In some definitions the upper limit of LEO is set at approximately 2000 km and MEO extends from above this boundary up to Geostationary Earth Orbit. According to an operational definition an orbit is classified as MEO if its perigee altitude is greater than 2000 km and its apogee altitude is less than 35786 km (approximately the 2000–35786 km band).

Orbital velocity and period depend on altitude. For example in circular orbits at the common MEO altitude of approximately 20200 km used in global positioning systems the orbital period is about 12 hours and the orbital velocity is approximately 3.9 km/s. Such positioning constellations employ multiple orbital planes with specific inclination angles.

Medium Earth Orbit - MEO (Generated by Artificial Intelligence)

Communication with Ground Stations and Coverage

The coverage footprint of MEO is larger than that of LEO therefore fewer satellites are required to achieve global or hemispheric coverage compared to LEO systems. Unlike Geostationary Earth Orbit satellites which appear fixed in the sky MEO satellites move relative to the ground therefore ground stations and user terminals must perform tracking and handover processes. In some communication architectures MEO is considered as an orbital option offering lower latency than GEO.

Applications

• Satellite navigation / positioning (GNSS): Medium Earth Orbit is the most commonly used orbital region for navigation satellites.
• Communication systems: MEO is evaluated in certain system designs as a compromise between latency and coverage between GEO and LEO.
• Observation / remote sensing concepts: Some studies report that MEO altitude coverage and radiation environment can be jointly considered for environmental monitoring missions.

Space Environment and Radiation Conditions

In some classifications the upper boundary of LEO (approximately 2000 km) is associated with regions where Van Allen belt effects become significant. MEO encompasses altitudes above this boundary and radiation effects are considered in mission design under headings such as electronics design shielding and redundancy.

Comparison of MEO with LEO and GEO

Advantages of MEO over LEO:

• Coverage geometry and satellite number efficiency: The ground coverage footprint of a single satellite in MEO is wider than that of a satellite in LEO. Therefore for a given coverage target (global or hemispheric) the required number of satellites and orbital planes can be reduced compared to LEO architectures.
• Visibility duration and handover load: Since MEO satellites move more slowly relative to ground terminals than LEO satellites visibility durations are extended. This reduces the frequency of handovers at the user or ground station side and simplifies tracking cycles relatively.

Disadvantages of MEO over LEO:

• Latency: Propagation delay increases with satellite-to-Earth distance. Although MEO provides lower latency than GEO it produces higher one-way and two-way latency than LEO.
• Link budget: Increased range raises free-space path loss. To maintain the same service level higher EIRP higher antenna gain narrower beam design or more sensitive receivers are typically required. This creates a disadvantage for user terminals compared to LEO particularly under size and power constraints.
• Radiation environment: The MEO band overlaps partially with or exhibits pronounced effects of the Van Allen belts. As a result shielding rad-hard component selection error tolerance and redundancy requirements become more critical than in LEO due to risks such as total ionizing dose (TID) single event effects (SEE) and internal charging.
• Debris sustainability: Atmospheric drag in MEO is very weak so satellites do not naturally deorbit and decay after mission end. This necessitates end-of-life disposal maneuvers and sufficient separation from the operational band; otherwise long-term collision risks and band congestion increase.

Advantages of MEO over GEO:

• Latency: MEO systems offer lower propagation delay than GEO due to shorter path lengths. This is an advantage over GEO particularly for interactive services and latency-sensitive applications.
• Coverage: GEO satellites appear at low elevation angles near the horizon at high latitudes increasing link margin and blockage sensitivity. With appropriate inclination and constellation geometry MEO can provide better elevation angles and more stable visibility at high latitudes (GNSS constellations are a typical example of this approach).

Disadvantages of MEO over GEO:

• Ground segment: While GEO satellites remain fixed in azimuth and elevation MEO satellites move across the sky. Therefore ground segments require tracking planning and handover processes and user terminals may need tracking capability or multi-beam solutions.
• Constellation requirement for continuity: GEO provides wide regional coverage with one or few satellites whereas MEO requires multiple satellites and multiple orbital planes for continuous service. This increases overall system complexity including satellite count ground segment control and operations.
• Long-term dynamics and resonances: In the MEO regime combined effects of Earth’s harmonics and Sun-Moon third-body perturbations can lead to long-term evolution in certain combinations of inclination RAAN and argument of perigee (e.g. eccentricity growth different regimes of node and perigee drift). This makes station-keeping strategies and especially end-of-life disposal orbit selection more critical.

Space Debris Density and Observation Studies

The MEO region is an actively used orbital regime alongside GNSS constellations. This region can be evaluated not only to include circular MEOs but also portions of highly elliptical transfer orbits. Studies on the MEO debris population consider optical scanning and tracking approaches in scenarios where highly elliptical and inclined orbits partially overlap with MEO.

End-of-Life and Disposal Approaches

In MEO atmospheric drag is weaker than in LEO so natural orbital decay is limited and end-of-life disposal plans are implemented. In some applications satellites are raised to separate disposal orbits above their operational altitude; in other cases they are left passive in their operational orbits. Since long-term orbital dynamics such as Sun-Moon-Earth gravitational perturbations and resonances can affect the evolution of disposal orbits the selection of disposal orbits and separation distances must be evaluated in conjunction with these dynamics.