geostationary orbit (GSO)

1. Geostationary satellites "parked" over equator travel at same direction and speed as Earth revolves. Each "footprint" covers 40% of globe. Directional antennae are aimed and fixed in position with no need for tracking

2. Satellites at lower orbits must travel faster than Earth revolves to avoid being pulled out of orbit by gravity, so they need tracking. Many do not follow an equatorial path

Credit: BBC

A direct, circular geosynchronous orbit at an altitude of 35,786 km (22,223 miles) that lies in the plane of Earth's equator. A satellite in this orbit always appears at the same position in the sky and its ground-track is a point. Such an arrangement is ideal for some communication satellites and weather satellites since it allows one satellite to provide continuous coverage of a given area of Earth's surface.

The first satellite was placed into geostationary orbit was Syncom 3 in 1964. It orbited above the Pacific Ocean and beamed pictures from the Tokyo Olympics to the US later that year – the first trans-Pacific TV transmission.

The possibility of spacecraft in geostationary orbits was first discussed by Herman Potocnik (who wrote under the pseudonym Herman Noordung) and Konstantin Tsiolkovsky. In 1945, Arthur C. Clarke discussed how a set of such satellites could form a global communications network.

Related category

• CELESTIAL MECHANICS

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