Quote:
Originally Posted by Barrie Yates
...Satellite surveillance is normally on a polar orbit although geo-stationary are used to cover areas of perceived threat or specific interest...
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Only if the area of interest can be seen from a satellite directly over the equator. A geostationary satellite is one that stays in the same place in the sky if you view it from a fixed position on the Earth. This can only happen for equatorial orbits.
Polar orbits are really used for mapping (which is surveillance of a sort, I suppose). This is because it takes so long for the satellite to return to one spot after its last pass over that spot.
A geosynchronous orbit can be used to view areas of interest, but it only returns to the same place once per day (minus a few seconds). Not much good if you want to survey the area at a different time to when it passes over.
Surveillance satellites are in normal elliptic orbits. They have to be higher than 100 miles in order to maintain an orbit. The higher they are, the more ground they can "see", but as you'd expect, it's at a lower resolution. Also, they have to travel at about 5 miles per second to maintain such a low orbit, so they can only see a particular site for a short time.
Surveillance satellites carry fuel so they can be retasked to a new orbit if events require it. When that fuel runs out, they are only good for photographing what's in their prevailing orbit until their orbit decays enough for them to shoot off into space or fall towards Earth. When a satellite is retasked, the fuel it needs is dependent on its altitude. A low-Earth orbit needs more fuel to change than a medium-Earth orbit.