What I fail to understand is that if a satellite can read a number plate, how the freak can it not see a plane
It's a question of knowing where to look... you can search along a flight plan, but that gives a very broad track, and doesn't allow for any deviation off route
As an example. You're looking for a red car travelling from London to Edinburgh. You know it left at noon, and should therefore arrive at about 6pm. It fails to arrive by nine, so you then go looking. Starting at Edinburgh and working south, you would look at the M1/A1/A1M corridors, tracing them back towards London until you found it.
But what if the driver had deviated from the plan and gone M40/M42/M6, then cut across from Carlisle to Edinburgh and stopped in Lancaster for the night
Using satellites, you would never find it
Also airspace is three dimensional, whereas the ground is by and large two dimensional...