how did they use the GPS (global positioning system, unless you are referring to something else) to communicate? to my knowledge, a GPS receiver works by timing how long it takes a signal to make it from the satellite to the receiver and then using that information to calculate the longitude and latitude of the receiver. this site is where I learned about it: http://www.howstuffworks.com/gps.htm . I might be wrong though; do you know any details about how they accomplished it?