posted on May, 1 2012 @ 05:49 AM
Geostationary satellites are in an orbit about 36000km above earth, i don't know the exact distance but its somewhere that height, and the orbit they
are in is almost circular, so they never get much lower than this.
Only this orbit has the unique feature that a satellite travels around the earth at the same speed the earth is rotating, thus having a direct
uninterrupted view on the same side of the earth all the time.
Satellites being up there have an ammount of fuel onboard and usually need that just for attitude control (pointing) and minor trajectory correction
for a little drift they develop over time.
imagine that a satellite,-and i read that from ASTRA-SES-, that a geostationary satellite has a virtual cube up there in space with a sidelenght of
about 160km , and that the control station keeps this satellite within this cube, using the onboard thrusters every once in a while.
These corrections are like once or twice in three month, and the satellites often have fuel onboard making them able to maneuver this way at least for
its designated lifetime, which can be 10 or more years.
Once the satellites are no more used they are maneuvered into a nearby 'parking-orbit' where they can stay almost forever, and noone really has to
care since its still in the range of 36000 km's
There was a case where a still functioning TV-Satellite developped an anomaly making it incapable performing its stationkeeping, but the attitude
control (in this case based on reaction wheels) was still working).
So TV-Enthsiasts (i guess it was the Asian zone which the satellite was build for) saw the Satellite drifting off its position.
This satellite worked for a long time, but since people are not that happy in constantly adjusting their satellite dishes compensating the drift, the
satellite wasn't that much used by major stations anymore.