NEWS RELEASE
`
`06/13/95
`CONTACT: Stanford University News Service (650) 723-2558
`A brief history of satellite navigation
`STANFORD -- Getting lost soon may be a problem of the past.
`The reason: the growing use of radio signals from satellites for navigation.
`With handheld receivers that cost less than $300, users can determine their position anywhere on the globe, provided
`they are outside and have a clear view of the sky. When combined with a computerized map, such receivers can
`pinpoint an individual or a vehicle's location on a given street within 30 feet.
`More than 60,000 of these receiver sets are sold each month, for myriad purposes. Rental car companies equip
`luxury cars with satellite receivers and computer maps to help customers navigate. Scientists use the receivers to
`study the movement of animals in the wild. Ambulance drivers calculate the shortest route to pick up heart attack
`victims. Geophysicists track the motion of earthquake faults.
`This revolution in navigation is the consequence of the development of a military satellite navigation system called
`the Global Positioning System/NAVSTAR, developed in the 1970s under the direction of Bradford W. Parkinson,
`now Stanford professor of aeronautics and astronautics, and a U.S. Air Force colonel at the time.
`On May 17, Parkinson discussed his experiences in the evolution of satellite navigation, which has spawned a whole
`new research area at Stanford under his direction. Current research, sponsored by the Federal Aviation
`Administration, includes contracts and grants exceeding $12 million. Specific research areas include control of small
`model aircraft and robotic farm tractors. More than 25 graduate students are involved in GPS-related research. Other
`Stanford faculty members involved are Robert Cannon, the Charles Lee Powell Professor of Aeronautics and
`Astronautics; Per K. Enge, research professor of aeronautics and astronautics; J. David Powell, professor of
`aeronautics and astronautics; and Bernard Widrow, professor of electrical engineering.
`The story of the system began Oct. 4, 1957, when the Soviets launched Sputnik, the first artificial satellite to orbit the
`Earth, Parkinson said in his lecture. Two researchers at the Johns Hopkins Applied Physics Laboratory in Baltimore -
`- William Guier and George Wiefenbach -- figured out a way to determine Sputnik's orbit simply by measuring the
`Doppler-induced changes in the frequency of the simple radio signal that it transmitted.
`Several years later, Parkinson said, another APL scientist, Frank McClure, was seeking a system that would allow
`Polaris nuclear submarines to keep precise track of their locations. He realized that this could be done by "inverting"
`the approach of Guier and Wiefenbach. That is, by measuring a radio signal from a satellite whose position is known,
`a submarine could determine its own position.
`McClure persuaded a colleague, Richard Kerschner, to design a system of satellites that would provide navigation
`information. The system, TRANSIT, began operating in 1964, with five satellites that broadcast two different tones.
`The use of two tones allowed the system to compensate for variable signal delays that occurred in the ionosphere.
`(One satellite became oriented upside down, its antenna pointing away from Earth, and due to limitations of its
`stabilization system could not be re-oriented. But the remaining satellites were adequate.) It took the submarines six
`to 10 minutes to get a fix, which was accurate to within 25 meters, Parkinson said.
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`Meanwhile, the Naval Research Laboratory and the Space and Missile Systems Organization of the U.S. Air Force
`favored different satellite navigation systems.
`The naval lab backed the TIMATION program, which used high-precision clocks to provide both accurate position
`and precise time measurements to ground observers. The time measurements improved the system by allowing more
`precise determinations of the satellite location and lengthening the time between required position updates. Two
`TIMATION satellites, each bearing a quartz clock accurate to one part per billion, were orbited: one in 1967 and the
`other in 1969.
`The Space and Missile Systems Organization pushed a program called 621B, which used a signal that employed
`pseudo-random noise to resist jamming. Unlike the various Navy systems, 621B provided altitude, as well as latitude
`and longitude. "To the Navy, navigation is essentially a two- dimensional problem, but the Air Force was definitely
`interested in the third dimension," Parkinson said. The 621B system was tested using aircraft between 1968 and
`1971.
`"There was a fierce competition, not just between the Navy and the Air Force, but also between Navy and Navy," he
`said. "The competition was over dollars. And there were also people like me -- who believed in using inertial
`guidance rather than external navigation systems -- standing around on the sidelines." Inertial guidance systems rely
`on sensitive accelerometers to keep track of an object's movements.
`Each of the systems had some major drawbacks, Parkinson said. TRANSIT fixes could be updated only four to six
`times a day, and if too many satellites were launched they would begin jamming each other. TIMATION was easy to
`jam and only two-dimensional. 621B needed continuous signals from a ground station to operate.
`In 1972, Parkinson was transferred by the Air Force to the 621B program over his objections, and thus got into
`satellite navigation through what he terms a "lucky failure."
`He soon was called upon to give an extended briefing on the system to the new director of research and engineering
`for the Department of Defense, Dr. Malcomb Currie. Currie liked the system and wanted to do something new, so he
`encouraged Parkinson on his many trips to Washington, D.C., to sell the program.
`In August 1973, the 621B proposal went before a streamlined Department of Defense decision- making process,
`called the Defense System Acquisition and Review Council (DSARC), that had been set up by David Packard in
`1972. In this process, all the decision-makers were convened in one room and projects voted up or down.
`"That was 'Black Thursday.' The DSARC panel said 'no' to the project," Parkinson recounted.
`But the rejection turned out to be another "lucky failure." Currie determined that what the panel wanted was a joint
`project, with all the services participating, and he put Parkinson in charge of pulling such a project together.
`Parkinson and a small staff met in an empty Pentagon over the Labor Day weekend in 1973, coming up with a
`system that incorporated the best features of each of the competing systems: the signal structure from 621B, the
`orbits and orbital prediction method from TRANSIT and the clocks from TIMATION. They called the new system
`Global Positioning Satellite/NAVSTAR. When the project went before the DSARC panel on Dec. 17, 1973, it was
`approved.
`"A message you might take from this talk is, 'You succeed better if you fail' or 'Failure is an essential catalyst for
`success,"' Parkinson said.
`The first "phase 1 bird" was launched in February 1978, on time and within budget, Parkinson said. When the system
`was up and running it provided positions accurate to within 10 meters. The signal was specially encoded so that
`civilian users were only able to obtain locations with an accuracy of about 50 meters. Nevertheless, civilians --
`surveyors being among the first -- immediately started finding uses for this new capability, Parkinson said.
`Today there are 25 GPS satellites in orbit: Six to 11 are normally in view at any given time at any point on Earth.
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`The GPS/Navstar development group had predicted that the military would have use for 27,000 GPS receivers and
`set of goal of making these for less than $10,000 apiece. Today, the number of military receivers is nearly 40,000, a
`modest number compared to the nearly three- quarter million civilian sets being sold annually.
`"Civilian use is clearly dominating military use," Parkinson acknowledged. Originally, there was some controversy
`about allowing non-military use of the GPS system. But after the downing of the Korean jetliner KAL 007 when it
`strayed into Soviet territory, President Reagan decided that GPS, which could reduce the likelihood of such
`navigational errors, would be made freely available to the airlines, shipping industry and other civilian users.
`Commercial interest has grown, particularly with the spread of differential GPS, developed by Parkinson's group at
`Stanford. Differential GPS uses GPS receivers and satellites in conjunction with a ground station, or pseudo-satellite,
`at a known position, to provide high-precision tracking in specific locations. The Stanford group has been developing
`differential GPS for use in an automatic landing system for commercial aircraft. Last October, the system was
`installed on a United Airlines 737 jetliner and flawlessly executed more than 100 blind landings.
`"Differential GPS has largely defeated the GPS encoding so I expect that the military will eventually turn it off,"
`Parkinson predicted. The number of civilian users is now so high that he does not think the government will be able
`to start charging to use the system, "although they may charge to make improvements."
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