What is a geostationary satellite?

It might be hard to imagine there is much difference between satellites. They go into space and orbit the Earth performing their roles. An orbit is an orbit, isn’t it?

There can be a distance of more than 35,000km between the satellites orbiting our planet.

This is deliberate; each satellite sent into space needs to be at the right vantage point for its job.

Geostationary satellites require phenomenal precision to put into the right places, but serve very important purposes. We will discuss their purposes and what exactly a geostationary satellite is, in this article.

What is a geostationary satellite?

Satellites in geostationary orbit (GEO) have been put into a region of Earth orbit some 35,780km above the surface. This places them tens of thousands of kilometres above the lowest orbiting satellites, which are still many times higher than the highest flying commercial aircraft.

GEO satellites possess a unique property due to the speed of their orbit and their positioning. Orbiting on the same plane as the Earth’s equator, they complete their orbits in tandem with the planet. This makes the satellites appear stationary in the sky to observers on the ground.

Geostationary and geosynchronous (GSO) are terms often using interchangeably to describe this type of orbit. Technically speaking, GEO is a particular type of GSO. GEO satellites will appear more or less completely still in the sky, whereas GSO satellites could appear to move up and down in the sky while matching the same orbit speed as Earth.

What does a geostationary satellite do?

GEO satellites stay in their ‘fixed’ positions above the equator and commonly are one of a few making up a small constellation. They move at speeds of about 3km per second to maintain their orbits.

Due to their lofty positions, just a handful of GEO satellites can create coverage for nearly the entire globe.

Since observers on Earth know that GEO satellites will be in the same location every time they need it, these particular spacecraft are much more convenient solutions to certain demands than satellites in other orbits.

How is a geostationary satellite used?

Geostationary satellites are useful for purposes where constant or frequent connection to the satellite is needed, such as telecommunications. Because the position of the satellites can be relied on, relays on the ground can be pointed at them without having to worry about their movement from the original position.

Other satellites moving in orbits out of sync with Earth would only be able to briefly make contact once or twice a day, making them unfit for functions that need 24/7 availability.

GEO is also used for weather monitoring and surveillance. They can keep track of fixed positions and monitor changes over time, making them highly useful for monitoring oceans and the progression of storms. Their altitudes from Earth give them the longest and widest possible views of the planet’s face.

Geostationary satellites also aid with satellite navigation systems and relay information to non-GEO satellites and stations. The European Space Agency uses GEO satellites for such purposes as part of their European Data Relay System.

How far are geostationary satellites from Earth?

Geostationary satellites orbit the Earth from roughly 35,780km away. This puts them in the highest true orbit utilised by humans, with the space 300km above being used as ‘graveyard orbit’ for satellites that can no longer serve their purpose.

GEO satellites that have ended their missions are moved to this orbit so as not to interfere with still-operational satellites.

Satellites orbiting closer to Earth fall into the categories of low Earth orbit (LEO) being within 2,000km of the planet’s surface, and medium Earth orbit (MEO) covering a region of over 30,000km between LEO and GEO.

Lowest LEO satellites can be around 160km from Earth, making the difference between the lowest satellite orbits and geostationary orbit almost 90% of the Earth’s entire circumference (roughly 40,000km). That’s quite a distance!

GEO vs LEO: What is the difference?

Apart from the gulf between the operational distances of LEO and GEO in relation to Earth, these two types of orbit differ in their typical applications.

LEO, being closest to the planet, is useful for satellite imaging. Images can be taken from satellites at high resolutions and without the vastly increased distance of GEO.

LEO is also more convenient for CubeSats, being easier and cheaper to achieve for their limited payloads. LEO is used for the International Space Station, facilitating astronauts’ travel to and from the station.

However, LEO is inconvenient for applications where GEO shines, such as telecommunications. Their relative closeness to the planet means that LEO satellites travel very fast – taking at most two hours to complete an orbit – making them harder for ground stations to track and rendering them unsuitable for stable uplinks.

GEO satellites are more reliable in terms of position, making them useful for purposes like observation and monitoring, as well as being relays for other satellites that can’t afford their stationary stability.

However, this stability means that geostationary satellites need to be above the equator and cannot deviate. This makes them unfeasible for polar orbits and limiting their view of the planet.

LEO can be achieved on tilted planes, granting them more available paths for their missions while ensuring they won’t collide with other satellites.

GEO is also more costly to achieve due to its distance, which introduces certain delays in information transfer.

The right satellite in the appropriate orbit can achieve its mission perfectly – this is why the purpose of a satellite is the biggest factor that will define its optimal orbit.

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