MEO Between GEO and LEO
Satellite communication uses orbital ranges with different coverage areas and propagation delays. Geostationary Earth Orbit (GEO) satellites orbit at 35,786 kilometers and appear fixed over one longitude, while Low Earth Orbit (LEO) systems use many satellites at lower altitudes to reduce path length and latency. GEO provides broad coverage from one spacecraft, whereas LEO requires a larger constellation and frequent handoffs. The longer GEO path also adds propagation delay to every user packet and gateway exchange.
Medium Earth Orbit, or MEO, occupies the range above roughly 2,000 kilometers and below 35,786 kilometers. Its altitude gives each satellite a larger coverage footprint than LEO and a shorter path than GEO. GNSS constellations use this range for predictable geometry, while systems such as O3b use it for broadband links with a smaller constellation than a comparable LEO service. The range covers several orbital regimes, so coverage, period, radiation exposure, and link budget still depend on the selected altitude and inclination.
The Dynamics of the Intermediate Orbit
Kepler's Third Law links orbital period with altitude. A satellite at a higher MEO altitude completes an orbit more slowly than a satellite in LEO, so the exact period depends on the selected orbit. NASA gives the GPS orbit as approximately 20,200 km with a 12-hour period; Molniya orbits can also have 12-hour periods but use high eccentricity. A semi-synchronous navigation orbit is one useful example, not a definition of every MEO system.
- Orbital Period: Common circular MEO examples have periods from about 2 to 12 hours, while the upper boundary of MEO approaches a 24-hour period.
- Visibility from Ground: A MEO satellite can remain above a ground station for several hours, depending on altitude and the elevation mask. A LEO pass usually lasts minutes. The usable interval begins when the satellite clears the minimum elevation and ends when it falls below that mask.
The Need for Constellations and Tracking
MEO satellites remain in motion relative to a ground station, even during a long visibility window. System design therefore combines constellation planning with antenna tracking. The receiver predicts the pass from orbital data and keeps the antenna pointed as the elevation and azimuth change.
Continuous global coverage requires a of multiple satellites. MEO's higher altitude gives each satellite a larger coverage footprint than LEO. A complete constellation can therefore use tens of satellites, with 20 to 30 as an example for a particular coverage geometry rather than a universal design value. The required count changes with the service area, minimum elevation, orbital planes, redundancy, and the continuity target for the link.
Communication terminals for MEO must track the moving satellite. A fixed dish used for GEO television cannot follow this path, so MEO ground stations use antennas on motorized gimbals. A service that requires continuity can use two antennas: one carries the active link while the other acquires the next satellite, enabling a "make-before-break" handoff. This arrangement keeps the first carrier active while the second terminal completes acquisition, which avoids a gap during a scheduled satellite transition.
MEO and Global Navigation Satellite Systems (GNSS)
Medium Earth Orbit is used by the main global navigation satellite systems. Its altitude supports broad coverage, predictable motion, and signal geometry suitable for positioning receivers. GPS, GLONASS, Galileo, and the MEO portion of BeiDou use measured time of flight from several spacecraft to calculate a receiver position and clock offset.
Trilateration in GNSS Positioning
GNSS positioning uses a geometric principle called . Each GNSS satellite broadcasts a precise timing signal. A receiver in a phone, car, or measurement instrument measures arrival-time differences from several satellites, converts them into distances, and intersects the resulting spheres. One distance defines a sphere around a satellite, two spheres intersect in a circle, and three spheres narrow the simplified solution to two points. A fourth measurement also solves the receiver clock offset and yields latitude, longitude, altitude, and time. The receiver also applies satellite ephemeris and clock data when converting the signal measurements into a position.
Why GNSS Uses MEO
MEO supports GNSS operation for several engineering reasons:
- Global Visibility: Nominal GNSS designs with about 24 to 30 satellites can provide at least four visible satellites across most of Earth when the constellation geometry and elevation mask are specified. The current operational count changes by system and date. Four measurements provide the basic position and clock solution, while additional satellites improve redundancy and geometry.
- Stable Geometry and Predictability: MEO satellites follow predictable paths and have a lower angular velocity than LEO satellites. The resulting distribution of visible satellites supports trilateration. Control segments can predict their ephemerides and publish timing data to receivers.
- Less Orbital Decay:At MEO altitude, residual atmospheric drag is low. The orbit therefore needs fewer drag-related corrections, which supports predictable long-term timing references. Station keeping still corrects perturbations from Earth's gravity field, radiation pressure, and the Moon and Sun.
Examples of GNSS Constellations
- GPS (Global Positioning System): The United States Space Force operates GPS satellites at an altitude of approximately with an orbital period of about 12 hours. GPS.gov lists a 24-slot nominal design and reports operational counts separately; a status presentation dated 2026-05-19 lists 39 satellites, with 32 marked healthy.
- GLONASS (Global Navigation Satellite System): Russia's global navigation system uses MEO at about , with a design of 24 satellites in three orbital planes and an orbital period near 11 hours 15 minutes.
- Galileo: The European Union's global navigation system is designed for civilian control and use. It operates at about in three MEO planes; ESA describes 28 satellites in its current system overview.
- BeiDou:China's navigation system, which uses a combination of GEO, MEO, and inclined geosynchronous orbit (IGSO) satellites to provide both regional and global services.
MEO Data Communications: O3b
GNSS is the largest MEO application by constellation count, while SES uses MEO for broadband communication through O3b. The name O3b refers to the "Other 3 Billion" and describes the original service concept for regions where terrestrial networks were limited. SES describes the original O3b service as a 20-satellite MEO constellation and later introduced O3b mPOWER as a second-generation system with a separate satellite fleet.
O3b mPOWER operates in an equatorial MEO at approximately . SES describes a round-trip latency of about for its service and publishes that value as an RTT target or SLA for specified products. Trunk mPOWERED materials describe packages from tens of megabits to multiple gigabits per second. The platform serves enterprise connectivity, telemedicine, cellular backhaul, maritime links, and government networks around the equator; measured latency depends on the service path and terminal. The value is an end-to-end service condition that includes the satellite route and ground equipment, so it is distinct from a free-space propagation calculation.
MEO Trade-offs in Multi-Orbit Systems
Medium Earth Orbit shows the trade-off between coverage footprint, propagation delay, constellation size, and ground equipment. Its engineering role depends on the service and orbit selected. A navigation receiver, a gateway terminal, and a broadband service can therefore use MEO with different hardware and performance targets.
- Advantages: MEO has lower propagation delay than GEO, can cover a larger area per satellite than LEO, and experiences little atmospheric drag. A MEO communication system can therefore use fewer spacecraft than a comparable LEO system for a selected coverage target.
- Disadvantages: Communication MEO systems require tracking antennas on the ground, and their propagation delay remains higher than in lower LEO systems. MEO paths can cross the Van Allen radiation belts, where high-energy charged particles require radiation-tolerant satellite electronics and add design mass, complexity, and cost. GNSS user receivers avoid large tracking dishes, but the spacecraft still require radiation design for their selected orbital environment.
Multi-orbit systems assign different tasks to LEO, MEO, and GEO. MEO remains the orbital range used by GPS, Galileo, GLONASS, and other GNSS constellations, while O3b demonstrates its role in broadband communication between terrestrial networks and remote sites.