GPS Navigation that talks

GPS has many advantages for the tracking of satellites orbiting the Earth. It provides unsurpassed observability because low-Earth satellites are able to track six or more GPS satellites, with tracking arcs amounting to about half of the user satellite orbit. This cannot be achieved by any ground-based tracking station. This ability also renders the method robust. There is a high level of redundancy because orbits can be determined with as few as two GPS satellites being tracked at any time. When four satellites are being tracked, GPS allows for real-time autonomous determination of the position of the satellite, with an accuracy equivalent to that obtained with non-precise ground tracking methods. If a precise dual-frequency receiver is used and data is processed together with ground based data, GPS possibly provides the best accuracy that can be achieved in precise orbit determination.

Future uses:

The relative navigation of two spacecraft (currently being validated).
The tracking of the launch and early-orbit phases of rockets.
The tracking of re-entering spacecraft, even to the point of autonomous landing