Definition | Geosynchronous orbit | Futura Sciences

In the long list of different trajectories that a satellite can follow in space, theorbit geosynchronous is part of the large class of orbits geocentric. The latter designate, as their name suggests, the trajectories described by a spacecraft which revolves around our Planet. The peculiarity of the geosynchronous orbit is that it is described in the same direction of rotation as the Earth. That is to say, from west to east.

The period of the geosynchronous orbit – which English speakers call Geosynchronous Orbit (GEO) – is equal to the rotation period sidereal of the Earth, approximately 23 hours 56 minutes and 4.1 seconds. Its altitude is exactly 35,786 kilometers above the geoid earthly. To simplify, we often speak of an orbit at 36,000 kilometers. An altitude that locates this orbit above the low Earth orbit on which remote sensing satellites are located and the International space station (ISS) and even medium Earth orbits, but below the high Earth orbits.

About a quarter of the satellites circling the Earth are placed in a geosynchronous orbit. © dimazel, Adobe Stock

Several types of geosynchronous orbit

Thegeostationary orbit is a special case of geosynchronous orbit. One in which the orbit is circular and presents a zero inclination. It is therefore in the equatorial plane. Thus a satellite in geostationary orbit appears motionless compared to an observer located on Earth. A characteristic exploited by telecommunication satellites or by weather satellites.

In general, a geosynchronous orbit may, however, have an inclination other than zero. Some geostationary satellites at the end of their life are for example placed on a geosynchronous orbit having an inclination of approximately 13 °. They thus allow the polar stations to communicate.

His eccentricity may also appear non-zero. The satellite that settles there no longer describes a circle, but an ellipse. The trace on the ground that he leaves is no longer symmetrical with respect to theEcuador.

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