Orbits
Satellites are deployed in defined orbits around a particular celestial body, most commonly the Earth. The geostationary Earth orbit (GEO) is of particular regulatory and operational significance due to its unique physical characteristics. GEO is located in the Earth’s equatorial plane at an altitude of 35,786 km above the Earth’s surface and is characterised by an orbital period equal to the Earth’s rotation period about its axis. As a result, a satellite in GEO appears fixed relative to the Earth.
A key advantage of GEO operation is that earth station antennas are not required to track the satellite across the sky and may remain fixed, pointing towards the nominal orbital position of the satellite. The principal limitation of GEO arises from its considerable distance from the Earth, which results in increased signal propagation delay. Consequently, certain applications requiring near real-time transmission and feedback, such as two-way voice communications, may experience reduced performance. GEO satellites are most commonly used for the broadcasting of television and sound programme services. All other satellite orbits are classified as non-geostationary satellite orbits (NGSO), as satellites operating in these orbits exhibit apparent motion relative to a fixed point on the Earth’s surface. The most commonly used NGSO regimes are low Earth orbit (LEO) and medium Earth orbit (MEO).
LEO typically extends from altitudes of approximately 200 km to 2,000 km above the Earth’s surface, while MEO generally ranges from around 8,000 km to 20,000 km. In order to provide continuous radiocommunication services from LEO and MEO systems, a constellation of multiple satellites is required to ensure that at least one satellite is visible from any given service area at all times. Due to their closer proximity to the Earth, LEO and MEO satellites benefit from lower propagation delays and reduced transmission power requirements compared with GEO systems.
LEO hosts a number of well-established space assets, including the International Space Station (ISS) and the Hubble Space Telescope. In recent years, LEO has gained increased regulatory attention due to the deployment of large constellations of small satellites, including nanosatellites, for scientific, research and educational purposes, as well as for the provision of electronic communications services. Notable examples include the Starlink satellite system operated by SpaceX and the Kuiper system proposed by Amazon, both of which aim to deliver broadband Internet access through constellations comprising many thousands of satellites.
MEO is primarily associated with global navigation satellite systems (GNSS), such as GPS and Galileo. It also accommodates satellite networks such as O3b, which provide broadband electronic communications services, particularly to remote and underserved areas, as well as to the maritime and aeronautical sectors.
A key advantage of GEO operation is that earth station antennas are not required to track the satellite across the sky and may remain fixed, pointing towards the nominal orbital position of the satellite. The principal limitation of GEO arises from its considerable distance from the Earth, which results in increased signal propagation delay. Consequently, certain applications requiring near real-time transmission and feedback, such as two-way voice communications, may experience reduced performance. GEO satellites are most commonly used for the broadcasting of television and sound programme services. All other satellite orbits are classified as non-geostationary satellite orbits (NGSO), as satellites operating in these orbits exhibit apparent motion relative to a fixed point on the Earth’s surface. The most commonly used NGSO regimes are low Earth orbit (LEO) and medium Earth orbit (MEO).
LEO typically extends from altitudes of approximately 200 km to 2,000 km above the Earth’s surface, while MEO generally ranges from around 8,000 km to 20,000 km. In order to provide continuous radiocommunication services from LEO and MEO systems, a constellation of multiple satellites is required to ensure that at least one satellite is visible from any given service area at all times. Due to their closer proximity to the Earth, LEO and MEO satellites benefit from lower propagation delays and reduced transmission power requirements compared with GEO systems.
LEO hosts a number of well-established space assets, including the International Space Station (ISS) and the Hubble Space Telescope. In recent years, LEO has gained increased regulatory attention due to the deployment of large constellations of small satellites, including nanosatellites, for scientific, research and educational purposes, as well as for the provision of electronic communications services. Notable examples include the Starlink satellite system operated by SpaceX and the Kuiper system proposed by Amazon, both of which aim to deliver broadband Internet access through constellations comprising many thousands of satellites.
MEO is primarily associated with global navigation satellite systems (GNSS), such as GPS and Galileo. It also accommodates satellite networks such as O3b, which provide broadband electronic communications services, particularly to remote and underserved areas, as well as to the maritime and aeronautical sectors.