geostationary orbits?

Question

why must the satellite's orbit lie in the plane of the equator?

Answer 1

A geostationary satellite is still orbiting the earth. Its orbit just takes it once around the earth every 24 hours.

If you placed a 24-hour-orbit satellite over the north pole, it obviously couldn't just stay there 24 hours a day. In 12 hours, it would have gone halfway around the earth, and it would be over the south pole.

If you placed the satellite at, say, 45 degrees latitude north of the equator, then in 12 hours, it would be at 45 degrees south.

If you place it on the equator, then in 12 hours it would still be over the equator. It would have gone halfway around the earth, but the earth will have rotated 180 degrees in those 12 hours, so the net effect is that the satellite stays over the same spot.

The same principle doesn't work at 45 degrees latitude. If you move a satellite halfway around the earth from 45 degrees north, 90 degrees east, then in 12 hours it would move to 45 degrees north, 90 degrees west (if the earth didn't rotate at all). Then rotate the earth 180 degrees around the equator... you'll find the that the longitude may be your original 90E, but your latitude will still have changed to 45S.

Hopefully that helps you envision how geostationary orbits work!

Answer 2

Geosynchronous orbits are not required to be above the equator. A ping-pong ball over a fan pointing upwards could be in geosynchronous orbit anywhere on earth.

The answer actually lies in the general size (MASS) of satellites. Satellites must be large enough to carry on thier tasks, yet small enough to be lauched by rocket. This limits their mass to within a small variance of size.

Satellites also must not travel significantly upwards or downwards. This EQUALIBRIUM of hieght is achieved by moving the satellite at a speed great enough to overcome earth's gravity. A satellite ten thousand times more massive would need to move at much greater speed. To achieve such speed, and yet be geosynchronous, it would need to be substantially higher in orbit.

Witness the moon. Though not geosynchronous, it neither falls into the earth, nor floats away, but keeps a reasonable equalibrium of height above the earth, inspite of its huge mass. This is because it moves at a high rate of speed, even though it is a quarter million miles away.

A satellite the size of a golfball could be substantially closer to earth. If a typical satellite were above, say, 45 degrees latitude, it would still need to travel at a high rate of speed to keep its height equalibrium. To be geosynchronous, and achieve that speed, it would need to be substantially higher above the earth than at the equator.

The higher the orbit, the longer the time required to bounce signals. Still, a satellite 100 miles above the equator is a long way from NY, London or Moscow.

Geosynchronous satellites not above the equator do exist. They are simply less practical for certain uses.

Answer 3

That is the only way that the satellite will remain stationary over one point on the earth's surface. Otherwise the satellite would appear to move up and down in the sky.

Answer 4

Because if it didn't it wouldn't be geostationary. The earth would be rotating beneath it.