Geostationary orbits allow satellites to focus on a single part of Earth, and that makes them ideal for
a large variety of applications. My question is: Why don´t all satellites use them?

Lucy Suver

Ann Arbor, Mich.

Like many of the best things in life, geostationary orbits come at a huge price. Maintaining a fixed position in relation to Earth, which is extremely helpful for communication, surveillance and other key functions, is a lot more complicated than finding a good parking space and staying put.

In a conventional low orbit, some 300 miles above the planet, maintaining a fixed position would require continuously firing rockets-which would demand more fuel than any satellite could possibly carry (though small, infrequently fired rockets can help maintain orbital altitudes).

To stay in sync with Earth, satellites in geostationary orbit exploit a neat trick of geometry-they fly about 24,000 miles above Earth, at which height their natural orbit matches the speed of Earth´s rotation-that is, it takes the satellite 24 hours to rotate around the planet.

But a high-altitude orbit has several disadvantages. Reaching it requires a considerable expenditure of fuel. From that height, camera resolution is diminished, and communication times are delayed by several seconds, because when a satellite is so far from Earth, signals take longer to reach it and then bounce back.

Consequently, geostationary orbits are generally used for weather satellites that assess entire hemispheres and â€non-live†communications satellites.

_Edited by Bob Sillery

Research by Eric Adams, Greg Mone and Jill C. Shomer