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Purveyors of the Cosmic 'Occult'
11.30.06
 
In the early 1960's, teams from JPL and Stanford University exploited radio links between Earth and the Mariner 3 and 4 spacecraft to probe the atmosphere and other properties of Mars. This aspect of radio science has become a staple of planetary exploration.

As GPS emerged in the 1980s, NASA devised new analysis techniques and equipment to enable precise positioning of points on Earth and of orbiting satellites. The quest for sub-centimeter global accuracy led to a fuller understanding of the perturbations of the GPS signals as they pass through the ionosphere and atmosphere. That soon led to GPS-derived measurements of the atmosphere and ionosphere that rivaled or exceeded existing capabilities.

JPL submitted the first GPS occultation proposal to NASA in 1988. Though that “GPS Geoscience Instrument” did not fly, the concept was established, and development of GPS remote sensing technology began. NASA began developing GPS remote sensing receivers, and global ground networks were put in place.

The GPS/MET experiment, proposed by the University Corporation for Atmospheric Research and sponsored by the U.S. National Science Foundation, employed NASA's first-generation TurboRogue receiver and global GPS ground network. Launched in 1995, GPS/MET was remarkably successful in measuring properties of the atmosphere and ionosphere with a low-cost and reliable instrument that also provided the host satellite with precise navigation and timing information.

NASA followed the GPS/MET success with experiments on six international partnership missions launched between 1999 and 2002, including the Oersted (Denmark); Sunsat (South Africa); Satelite de Aplicanciones Cientificas-C, or SAC-C (Argentina); Challenging Minisatellite Payload, or Champ (Germany); Gravity Recovery and Climate Experiment, or Grace (Germany); and FedSat (Australia). The lessons learned in these early missions refined the systems and techniques of GPS sounding, setting the stage for Cosmic—the first operational GPS occultation constellation. These pathfinder satellites demonstrated the robust low-cost technology. Several of these satellites continue to provide high-quality GPS remote sensing data today.

In 1998, the University Corporation for Atmospheric Research partnered with Taiwan's National Space Organization to take GPS remote sensing to the operational level with Cosmic, which is known as FORMOSAT-3 in Taiwan. For the science GPS receiver, the Cosmic team turned to JPL's second-generation BlackJack space receiver, now proven on Champ, SAC-C and Grace. JPL transferred the technology to Cosmic industrial partner Broad Reach Engineering, Golden, Colo., resulting in Cosmic's Integrated GPS Occultation Receiver.

 
 
Media contacts: Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.