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The Origins, Status, and Future of GPS

Presentation by Prof. Bradford Parkinson of Stanford University

October 7, 2003

Origins and heritage

In the current era of inexpensive, pocket-sized GPS receivers, when precision satellite guidance for everything from bombs to luxury cars has become ubiquitous, it is tempting to take the Global Positioning System for granted. But today's GPS is the product of a long and complicated history—a history witnessed firsthand by Professor Bradford Parkinson of Stanford University. Parkinson, who led the team that developed the first generation GPS system in the early 1970s, highlighted the development process and possible future directions for the satellite navigation at an Advanced Transportation Technologies seminar Oct. 7, co-sponsored by the ITS Institute and the Department of Aerospace Engineering and Mechanics.

GPS is not the first global satellite-based navigation system to be proposed. The Air Force and Navy, two organizations with a lot to gain from reliable worldwide navigation, developed three separate prototype systems in the late 1960s. However, technological limitations of the Transit, Timation, and 621B systems, combined with policy factors within the Department of Defense, resulted in federal funds being redirected to the development of a joint program.

Parkinson actively participated in the historic Labor Day 1973 meetings at the Pentagon which laid the foundations for a system that would incorporate and improve the best aspects of existing systems. In February 1978—44 months after contract authorization—the first GPS satellite was launched into orbit.

GPS satellites were the first satellite to carry atomic clocks into orbit, giving the new system a timing accuracy of one second in 317,000 years. This level of accuracy is critical, Parkinson pointed out, because in order to compute a location relative to a satellite in three dimensions, the user effectively has to know the satellite's location in four dimensions, i.e. it is necessary to know where the satellite was at the moment the timing signal was broadcast, so that transmission time and atmospheric delays can be factored out.

Current applications and research

Today, the number of GPS applications in both military and civilian sectors is exploding. Civilian receivers , some of which are priced at under $100, are selling at a rate of 200,000 per month. Civilian vehicle uses have expanded beyond commercial trucks and automobiles to include new farm tractors. In science, GPS is being used to track almost anything that can carry a receiver, from the edges of tectonic plates to grazing sheep.

High-accuracy GPS, which improves on the meter-scale accuracy of civilian receivers by adding a timing correction signal from a station on the ground or a private satellite, is rapidly gaining momentum. The ITS Institute uses differentially corrected GPS (DGPS) in several vehicle-based research projects, including the SAFEPLOW and the TechnoBus. This technology has also found wide application in civilian airports, where it can be used to enhance the safety of aircraft takeoffs and landings in low-visibility conditions.

The future

With GPS established as an increasingly ubiquitous utility for precision timing and navigation, Parkinson has turned his attention to the future enhancement of the system. He foresees an era of GPS improvements including accuracy upgrades, "hardening" the system against signal interference, and adding redundancy in terms of satellite geometry and broadcast frequencies.

However, these improvements are not assured. Just as in the original development process, technological challenges and policy limitations within the funding organizations have a profound impact on the evolution of the GPS system. As an example, Parkinson pointed out the current regulatory wrangling surrounding the open frequency bands that could be used by the GPS system—or by other, unrelated broadcast technologies with strong backing in the legislature. And competition to the U.S. controlled GPS network has recently emerged in the form of the European Galileo project.

Parkinson predicts that by 2010 there will be more than 50 million GPS users, including automobiles, ships, farm vehicles, aircraft, and virtually every other tracking and dispatch system in the world. Within just five years, every significant military system will depend on GPS in some way; this reliance will continue to drive improvements in precision and jam-resistance. The world's most ubiquitous navigation and timing system will continue to evolve, in a process shaped both by advances in technology and by the shifting policy landscape of the federal government.