geostationary orbit (GSO)
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.
| 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
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
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.