Describe briefly the main benefits and shortcomings of communication satellite?

Question

Describe briefly the main benefits and shortcomings of communication satellite systems
including for example, their orbits, propagation delays, the nature of the radiation and the
antennae used, and energy requirements.

Answer 1

Wide open question.

Satellites use solar arrays to make electricity to run their transmitters. Satellites don't have a lot of power available so their signal when it reaches the ground is very weak. The following parameters are tradeoffs:

Antennas: Large antennas on board spacecraft can focus energy on small earth area. Coverage goes down but the energy in the covered areas goes up. Direct TV is like that. Entire earth coverage means smaller comsat antennas but larger earth based antennas.

Information rate (or bandwidth): If we want large earth coverage but don't want large earth based antennas, then we don't get much bandwidth. GPS is like that. GPS satellites cover whole earth and receiving antenna on earth is often just a whip antenna but the information rate is very low compared to TV, for example.

There are four main classes of orbits: GEO, HEO, MEO and LEO. GEO gives good coverage for ground stations in mid latitutes but they are low on the horizon for stations near the poles. Also GEOs are a long way away so more energy is needed both at the satellite and the ground station. HEOs are Highly Elliptical Orbits which work well for polar based stations. Canada, I think, has a HEO. LEO is low earth orbiting and MEO is medium earth orbiting. Power required is much lower but since satellites move rapidly across the sky usually some kind of tracking antenna is needed on the ground unless the bandwidth is low. The IRIDIUM network is LEO. Takes many satellites for whole earth coverage. MEOs are half way. Slower moving across sky; fewer needed for whole earth coverage but more power needed.

This could go on for hours.