NASA researchers have demonstrated the ability to very
precisely navigate airplanes in real time, anywhere in the
world, independent of local navigational aids or
infrastructure. The breakthrough will not only benefit
scientists, but promises to extend precision navigation to
infrastructure-poor areas of the world, potentially
enhancing aviation safety in these areas.

Ron Muellerschoen, lead architect of the NASA Global
Differential GPS system at NASA’s Jet Propulsion
Laboratory, Pasadena, Calif., has demonstrated the ability
of the system to achieve real-time aircraft positioning
accuracy of 10 centimeters (3.9 inches) horizontally and 20
centimeters (7.9 inches) vertically, anywhere in the world?
a factor of 10 improvement over current autonomous
navigation systems. The system relays precise, real-time
navigation data to specially equipped aircraft. The JPL
team’s results were presented recently at the Institute of
Navigation Global Positioning System (GPS) 2002 Exhibit in
Portland, Ore.

Although developed to improve the accuracy, efficiency
and timeliness of Earth science missions, the technology’s
by-products may also include numerous civil and commercial
applications in such areas as aviation safety, marine
operations, land management, transportation and
agriculture, said Dr. Yoaz Bar-Sever, the principal
investigator for NASA’s Global Differential GPS system at
JPL. “Civil and commercial navigation services, currently
only available within Earth’s infrastructure-rich regions,
could now be extended to any part of the world without
lowering performance and with little to no marginal cost,”
he said.

Within the field of Earth science, Bar-Sever said the
technology would be used to develop better exploration
techniques for Earth observing instruments flying aboard
aircraft and spacecraft. “The ability of Earth science
instruments to precisely and autonomously know their
position and velocity in real time is critical to many
Earth observing applications, including monitoring and
responding to natural hazards such as earthquakes,
volcanoes and hurricanes,” he said.

JPL’s Airborne Synthetic Aperture Radar Group has
already used the precise real positioning from the Global
Differential GPS system to improve the resolution of Earth
images from NASA’s aircraft-based Airborne Synthetic
Aperture Radar instrument, said Group Supervisor David
Imel. Imel envisions even greater use for the system in
the near future. “For missions where an aircraft must fly
exactly the same flight profile repeatedly, in order to
sense subtle changes in the Earth from one flight to the
next, the need for the extremely precise navigational
accuracy that this system provides is critical,” he said.

In space, precise onboard knowledge of position will
improve the efficiency of a spacecraft’s onboard data
processing and reduce the time needed to transmit data to
the ground. Bar-Sever and his team have already conducted
successful demonstrations of decimeter-level real-time
satellite positioning using data from NASA’s Jason-1
spacecraft and the Argentinean Satelite de Aplicaciones
Cientificas-C satellite. The team is currently developing
a prototype payload to be flown aboard a spacecraft.

The NASA Global Differential GPS system flight
demonstrations were conducted over the United States and
Greenland in February through September 2002 aboard a NASA
Airborne Synthetic Aperture Radar DC-8 aircraft from NASA’s
Hugh L. Dryden Flight Research Center, Edwards, Calif., and
a NASA P-3 aircraft from NASA’s Wallops Flight Facility,
Wallops Island, Va.

Developed and operated by JPL since 1999 for NASA’s
terrestrial, airborne, and spaceborne science applications,
NASA’s Global Differential GPS system provides end-to-end
capabilities for autonomous, real-time orbit determination
and positioning at unprecedented levels of accuracy and
availability. The system processes real-time GPS data from
a global network of more than 30 dual-frequency GPS ground
sites. It is the only system in existence that provides
global, multiply redundant, real-time coverage of all GPS
satellites, all the time. It routinely and automatically
produces the most accurate real-time estimates of GPS
satellite orbits and clocks, media calibrations and many
other products and performance metrics. The system
leverages NASA investments in the global GPS network and
the U.S. Government’s investment in the Wide Area
Augmentation System navigation technology developed at JPL.

NASA’s Earth Science Technology Office funds the
development of the Global Differential GPS system, with
support from the Solid Earth and Natural Hazards Program
within NASA’s Earth Science Enterprise, Washington, D.C.
More information about the Internet-based Global
Differential GPS system is available online at:
http://gipsy.jpl.nasa.gov/igdg/ .

The California Institute of Technology in Pasadena
manages JPL for NASA.