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YPG testing critical to development of GPS
Technological change alters the world and becomes so common that radically transformative inventions eventually are taken for granted. The Global Positioning Satellite (GPS) system, tested at YPG for 16 years, is such an example.
Currently consisting of 31 satellites in orbit around the Earth, the GPS system allows anyone with a handheld receiver to pinpoint their exact geographic location with astonishing accuracy. Today, the technology is used not only by military personnel and testers at Yuma Proving Ground, but by millions of civilian consumers around the world as a navigational aid in automobiles, aircraft, and boats, by owners as a means of tracking lost pets wearing a GPS-enabled collar, and even by hikers and casual participants in the pastime called “geocaching,” a treasure-hunting game that utilizes GPS coordinates.
Few, if any of these users realize YPG tested GPS from the earliest days of its existence.
“It was the biggest single project the proving ground was ever involved in,” Bob Mai, then-associate director of the Range Support Directorate, said in a 1994 interview. “It paid a lot of bills for YPG for a long time.”
Yuma Proving Ground was the home of GPS testing from 1974 through 1990. YPG testers attracted the program by demonstrating their ability to collect more data at a lower price than other test ranges. Whereas other test ranges of the period gathered position, acceleration and trajectory data of test items with electro-optical trackers called Cinetheodolites, recently completed testing of the AH-56 Cheyenne attack helicopter had given YPG an edge.
The proving ground owned and used a then-state-of-the-art laser tracker that had a far greater range and comparable accuracy to a battery of Cinetheodolites. Further, engineers at the proving ground had adapted room-sized 1960s vintage IBM computers with specialized software that allowed them to collect test data from range instruments and onboard telemetry devices in real time, a groundbreaking advancement that dramatically reduced the time and cost of testing.
“YPG didn't have supercomputers,” said Bill Heidner, curator of YPG's Heritage Center. “We had sharp people writing algorithms for hand-me-down computers that made real-time data reduction possible.”
Added retired Air Force Maj. Jim Bybee, who worked on the GPS program from 1975 to 1982 and retired as officer in charge of GPS testing at YPG: “YPG was already ahead of the state of the art, which is why the Air Force came here. That they had laser trackers integrated into real time was a tremendous cost savings.”
When evaluations began in March 1977, the launch of the first GPS satellite was more than a year away and, like today, a GPS user needs coordinates from four satellites to get an accurate location reading. YPG testers coped with this by creating an “inverted range” made up of satellite simulators located in ground-based shelters at four different places.
Ground tests of the infant technology were conducted from modified 2-1/2-ton trucks, and aircraft used for testing were outfitted with antennas on the bottom of aircraft to pick up simulated signals from the ground receivers. The earliest GPS systems were so large that a UH-1 helicopter, which carried as many as 14 troops at a time when used in Vietnam, could only accommodate a pilot and two passengers when carrying a GPS device. By September 1977 over 70 test flights with UH-1 helicopters and F-4, P-3 and C-141 airplanes had been conducted.
“The UH-1 and the C-141 were real workhorses for us,” said Bybee. “But the C-141 cargo plane was large enough to fit three different contractor systems inside, so we got a lot of bang for the buck with them.”
As the Air Force began to launch GPS satellites, evaluators used position information beamed from the satellites instead of the inverted range receivers. This created new test challenges, however.
“The satellites gradually change position,” said Bybee. “As they launched more satellites, we had a pretty good test period for three or four hours per day. But every two weeks, we had to move back our testing by half an hour. We went around the clock at least three times in the time I was here.”
Though the continual changing of work hours was difficult for the scores of range workers involved with the testing, YPG's vaunted flexibility in range scheduling always gave testers the opportunity to make the most of the situation. This was accomplished even as another monumental program, the Apache Longbow attack helicopter, began testing at the proving ground in the late 1970s.
“The satellites being available for only a few hours a day gave us an urgent requirement to test whenever we could,” said Bybee. “We also didn't have to compete for range space at YPG. The ranges at other locations were consistently tied up, but at YPG we always had top priority.”
By the early 1980s, GPS technology had been miniaturized to the point that a man portable backpack weighing a mere 25 pounds began testing with soldiers at the proving ground.
“We had a good group of people at YPG and in the program office,” said Bybee. “There was a lot of high level interest in the program, and everyone was pretty attuned to how important the project was.”
Mark Schauer writes for The Outpost, the newspaper at Yuma Proving Ground.