Bradford Parkinson and Hugo Fruehauf: Inventing GPS

10 September 2019


Hugo Fruehauf and Bradford Parkinson recently appeared on BBC Inside Science to discuss their incredible, world-changing innovation: the Global Positioning System. Both engineers made a crucial contribution to the development of the revolutionary system, which opened up navigation to people all around the world. In February 2019, Bradford and Hugo, along with Richard Schwartz and James Spilker, Jr, were awarded the Queen Elizabeth Prize for Engineering for their pivotal roles in creating GPS.

In the 1960s and 70s, the US Navy developed a rudimentary satellite navigation system called Transit, using a constellation of just 5 satellites. This gave locations in two dimensions, and returned navigational positions once per hour. The Department of Defense wanted to advance this system, but the Navy and the Air Force had competing ideas as to how it would work. The Navy was happy to expand their current setup, but the Air Force required additional altitude data in three dimensions.

Bradford Parkinson, then an Air Force Colonel, was tasked with coming up with a new concept to meet the needs of both groups.

On Labor Day in 1973, Brad called a strategic meeting in the Pentagon, to decide on the future direction of the GPS project. He outlined how his new concept would work for the Air Force, but also for the rest of the world. Within three months, he had approval to start work on creating a full-scale demonstration of the system.

The chief engineer for the company tasked with creating the satellites was Hugo Fruehauf. Hugo’s game-changing contribution to the project materialised in the form of highly accurate atomic clocks. GPS satellites need to tell the time with extreme accuracy, in order to work out how long it takes a signal to travel from the satellite to a user on the ground. This then enables the distance from the satellite to be calculated, and data from four satellites can be combined to pinpoint a location.

Hugo’s concept involved placing atomic clocks inside the satellites themselves, rather than on the ground, as previously planned. Sending the satellites into space meant that they had to be miniaturised, which created another engineering challenge.

The technology was initially intended for military purposes, so the engineers introduced a ‘dither’ for non-military usage. This enabled the ground controller to limit acces and accuracy, which was initially set at 100 metres for the general public. Later, it was decided that GPS would be available to civilians at an improved accuracy of around three metres, and the technology began to be taken up by all kinds of industries, from fishing to forestry.

Listen to the BBC Inside Science podcast to find out more about Brad and Hugo’s story, and their views on the development of new GPS applications since its inception.

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