Global positioning systems
I'm sure there is an obvious answer to this, but I've been thinking about GPS and how it works. It takes a minimum of three satellites in orbit each sending out a signal that your receiver picks up and then calculates the distance to each satellite and hence your position in relation to them. Now that's fine.
How do the satellites know where they are? If all of the satellites were one arc second out of position i.e. the net is as expected just slightly rotated out of position, what system is built in that tells the satellites where they are?
Cheers.