Understanding Geosynchronous Orbits for Communication Satellites

[jaypee]

Communications satellites must be in geosynchronous orbits. That is, they must remain above a fixed point on Earth’s surface, enabling sending and receiving antennas to be aimed at a fixed point overhead. What, then, must be a communication satellite’s orbital period (the time for one complete orbit around Earth)?

 

[Loren Booda]

Sounds like a textbook problem. My guess is that, relative to the Earth, the orbital period is infinite, relative to the Sun, 24 hours, and relative to the cosmic background, 23 hours 56 minutes 4.09 seconds.

 

[russ_watters]

Booda is correct and that should be self evident. Clarification though - comms satellites do NOT necessarily need to be in geo orbit. If you have enough of them you can ensure one is overhead at all times.

 

[MrCaN]

Yes, communication satelites can broadcast over wide areas, so not all systems need to be in a geo-sync orbit, the main systems that use geo-sync are TV, because they can't afford 20 satellites to cover all the Earth at once, that is why you always point your dish towards the equator.

 

[russ_watters]

the main systems that use geo-sync are TV, because they can't afford 20 satellites to cover all the Earth at once, that is why you always point your dish towards the equator.

Actually given the expense of launching a satellite into geo orbit, I believe the reason they do it with tv satellites is the difficulty in having every dish actively track satellites.