Aren't GPS satellites in the same LEO (low earth orbit) as these satcomm birds?
Keep the sextant polished as well!
Edit: I discovered they aren't LEO (http://en.wikipedia.org/wiki/Low_earth_orbit
) like some satcomms...they are in the middle range between that and geostationary.
"Orbiting at an altitude of approximately 20,200 kilometers (12,600 miles or 10,900 nautical miles; orbital radius of 26,600 km (16,500 mi or 14,400 NM)), each SV makes two complete orbits each sidereal day, so it passes over the same location on Earth once each day. The orbits are arranged so that at least six satellites are always within line of sight from almost anywhere on Earth."
That means they are subject to cosmic rays, solar storms, "outages" and whatnot, but aren't likely to be dragged down by atmospheric expansion or other issues affecting LEO birds like Globalstar: http://en.wikipedia.org/wiki/Globalstar
Wikipedia: the sailor's pal.