Global Positioning System - WAAS Related

The U.S. Air Force's GPS constellation includes at least 24 operational satellites in 12-hr orbits. These satellites provide navigation and positioning services for both military and civilian users. JPL has developed techniques to rapidly determine very precise (centimeter-level) orbits for low-Earth orbiters such as the Topex/Poseidon satellite, which enables daily monitoring of global climatic and ocean changes, such as the El Niño and La Niña phenomena.

The GRACE mission (2001 launch) will improve knowledge of the gravity field by orders of magnitude through precise GPS and satellite to satellite tracking. In addition, JPL and NASA participate in ground-based GPS networks to measure crustal deformation to the few-millimeter level. This research activity will ultimately lead to a better understanding of earthquake mechanisms and may enable us to better anticipate their impact on populated areas.