A geostationary orbit, is a type of geosynchronous equatorial orbit (GEO), is a circular geosynchronous orbit 35,786 kilometres (22,236 miles) above Earth’s equator and following the direction of Earth’s rotation.
An object in such an orbit has an orbital period equal to the Earth’s rotational period, one sidereal day, and so to ground observers it appears motionless, in a fixed position in the sky. The concept of a geostationary orbit was popularized by Arthur C. Clarke in the 1940s as a way to revolutionize telecommunications, and the first satellite to be placed in this kind of orbit was launched in 1963.
Communications satellites are often placed in a geostationary orbit so that Earth-based satellite antennas (located on Earth) do not have to rotate to track them, but can be pointed permanently at the position in the sky where the satellites are located. Weather satellites are also placed in this orbit for real time monitoring and data collection, and navigation satellites to provide a known calibration point and enhance GPS accuracy.
Geostationary satellites are launched via a temporary orbit, and placed in a slot above a particular point on the Earth’s surface. The orbit requires some stationkeeping to keep its position, and modern retired satellites are placed in a higher graveyard orbit to avoid collisions.
The orbital period is equal to exactly one sidereal day. This means that the satellite will return to the same point above the Earth’s surface every (sidereal) day, regardless of other orbital properties. For a geostationary orbit in particular, it ensures that it holds the same longitude over time. This orbital period, T, is directly related to the semi-major axis of the orbit through the formula:
- {\displaystyle T=2\pi {\sqrt {a^{3} \over \mu }}}
where:
- a is the length of the orbit’s semi-major axis
- {\displaystyle \mu } is the standard gravitational parameter of the central body.
Difference between GEO and GSO
Different orbits
