The evolution of GPS satellites and their use today

September 16, 2020  - By
1960: ARPA launched Transit, the first satellite in what would become the world’s first GPS. (Photo: U.S. Army/DARPA)

1960: ARPA launched Transit, the first satellite in what would become the world’s first GPS. (Photo: U.S. Army/DARPA)

Sixty-three years ago, on Friday, Oct. 4, 1957, the Space Age began — most everyone alive today is a progeny. The Soviet Union sent a shiny, metal, beach-ball-sized sphere into orbit. Sputnik beeped every second for 21 days before going silent. Its beeps were heard ’round the world. Using the Doppler effect, a listener could tell whether the tiny satellite was moving toward or away from them. Scientists pinpointed the satellite’s exact location by observing it in a single pass, and realized the reverse could also be true. A terrestrial observer’s unknown location could be derived from the known orbit of a single satellite. That idea turned into the first satellite navigation system.

In 1964, the Navy Navigation Satellite System (NNSS) became operational. The highly classified system called Transit was built to support the Polaris ballistic missile submarine fleet. It operated on a small constellation of less than five polar orbiting satellites. With so few satellites in orbit, it could take more than an hour to get a positional fix. Twenty-meter accuracy could be attained by using specially encrypted signals, but these were restricted to submarines. All other users of Transit could only achieve accuracy within 200 meters.

Accuracy was a challenge. The problem was solved the same way John Harrison’s chronometer solved it 300 years earlier, threading together the past and present. More accurate location required more precisely measuring time (see The problem was solved by two Timation satellites launched in 1967 and 1969 to broadcast a time reference signal. Essentially, the Timation satellites were space-based chronometers.

Timation improved location accuracy, even though it took hours to achieve sub-meter precision. It proved a success, and as a result, in 1967, Transit became available for non-military users, such as surveyors. In fact, everyone today who has ever worked with a reference system is familiar with WGS 84, which was originally based on “Doppler surveying receivers” called georeceivers, referring to measurements from the Transit system. Transit was also known as NavSat as it became more broadly adopted for civilian purposes such as commercial shipping.

In 1973 the Department of Defense sought to combine the success of Transit (NNSS) and Timation into one satellite system, which evolved into the NavStar-Global Positioning System. The first launches began in 1978 and reached a full constellation of 24 GPS satellites in 1993. Since that time, Russia, Europe, China, India and Japan have all created their own constellations. All of those systems combined with GPS make up the global navigation satellite system (GNSS), which totals more than 120 satellites.

Recognizing GPS’s sustained success and positive global impact, in February 2019 the Queen Elizabeth Award for Engineering went to four of the primary developers of the GPS program for their contribution to the world. These four gentlemen are Engineering Stars. On Feb. 12 of this year, President Trump signed an Executive Order further acknowledging the value of position, navigation and timing (PNT) as the invisible infrastructure of modern society. And, on July 1, Capt. “Sully” Sullenberger addressed the Space-Based PNT Advisory Board, stating how GPS has become a universal part of every facet of our lives including financial transactions, transportation, agriculture, rescue operations, surveying and construction.

The GPS satellites are our own constellation and each of them should be named in honor of a scientist or engineer who helped conceive and develop the Transit, Timation and GPS programs; even though the earlier systems no longer exist, their legacy should long be remembered.

From those Cold War origins of a chirping beach ball traveling through space 63 years ago, now more than 2,600 satellites enhance our terrestrial lives providing better communication, location and understanding. We are all children of the stars, albeit stars of our own making.