NASA is developing a navigation system that augments GPS signals via a satellite phone network so that it works around the globe, beyond the limited implementation of WAAS. Their intended application is a UAV based mapping function utilizing synthetic aperture radar technology which requires a highly stable and accurate platform.

For testing purposes they will mount the radar and navigation system on a Gulfstream III (I especially like this part), "Since the Gulfstream III operates outside civilian air space it will not need a permit to use the UAV which takes 90-days due to a somewhat archaic processing system." I guess we're not the only ones frustrated with the FAA, even the best & brightest at NASA have a hard time with the red tape!

For details see article:

Nasa Develops Highly Accurate Plane Nav System

The PPA system will help keep the C-20A Gulfstream III flying level so the UAVSAR radar pod can scan geoseismic hot spots.