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  • Writer's picturePatrick Mullane

GPS - The accidental invention

Updated: Jun 4, 2020

I read a great book a while ago called Where Good Ideas Come From: The Natural History of Innovation by Steven Johnson. In it, Johnson explores exactly what the title suggests; he uses some awesome real-world cases to illustrate seven patterns behind innovation and inspiration. One of those cases involves the story of two scientists at the Johns Hopkins Applied Physics Laboratory (APL) named William Guier and George Weiffenbach and the power of sharing hunches and experiments with colleagues while trying to solve a problem.  

Guier and Weiffenbach were employees of APL in October of 1957 when the U.S.S.R. launched Sputnik, the world's first artificial satellite. It was an event that shocked the world in an era when tensions were high and the ability of a country to loft a payload into space was a signal that that nation was on the path to making the intercontinental ballistic missile (ICBM) possible. 

Sputnik (Photo Credit: Air and Space Museum)

The Soviet Union had concerns that nobody would believe that they had actually accomplished what they did and so they made sure Sputnik could emit a signal that could be tuned and listened to. Guier and Weiffenbach, the curious nerds that they were, used equipment they had to dial in the 20 Mhz signal and, like many Americans, became mesmerized by it. But their curiosity didn’t stop there, they began to wonder if they could study the doppler shift of the signal to determine the satellite’s speed. 

You may remember studying the doppler effect in high school. The common example given in most textbooks is that of the train passing a stationary observer while the train’s horn is blaring. The perceived frequency of the noise heard by the observer increases as the train gets closer to the stationary listener and decreases as the train fades into the distance, an effect caused by the compression (and decompression) of the sound waves emitted by the moving horn. Guier and Weiffenbach used their understanding of the doppler effect to run some numbers and did, indeed, calculate an orbital speed exceptionally close to that of Sputnik. Not content to only know the velocity of the Soviet satellite though, our fearless scientists chatted with some colleagues and they realized that by studying the slope of the doppler shift, they could approximate the altitude of the Sputnik as well. They then reserved some time on their shiny new UNIVAC computer to, over several weeks, calculate with amazing accuracy the orbit of Sputnik.

That story in and of itself is cool enough. But believe it or not, it gets cooler. Guier and Weiffenbach’s boss, the director of APL’s research center, Frank McClure, asked the pair if they thought they could use what they’d learned to answer another question. That question was this: if they could determine the position of a satellite from a fixed location on earth, could they determine a location on earth from a satellite in a known position? Guier and Weiffenbach gave the question some thought and determined that there was no reason - theoretically - that they couldn’t solve this problem, which became known as “the navigation problem.” They then went on to prove that it was indeed possible. 

Guier, McClure, & Weiffenbach (Photo Credit: APL)

What they didn’t know at the time is that McClure had a specific reason for asking them to do this work. The U.S. had developed the Polaris Missile, a nuclear-tipped missile that could be launched from a submarine, in an effort to counter the Soviet threat. But in order to target the Polaris well, it needed to know the position of the submarine it would be launching from. After all, it’s hard to get directions to your destination if you don’t know your starting point. Guier’s and Weiffenbach’s calculations helped McClure refine his idea for a satellite navigation system based on a series of satellites emitting signals that an instrument could receive and use to calculate its position on earth. Here’s how it all unfolded according to Guier and Weiffenbach themselves in the Johns Hopkins APL Technical Digest:

We learned later that many were concerned about navigating Polaris submarines such that a launch location at sea would be accurately known, ideally within a few hundred feet. In particular, Mac [McClure] had been spending part of his time downtown in the Navy’s Special Projects Office, which was responsible for development of the Polaris system and was aware of this serious problem in submarine navigation. He realized that the Doppler satellite tracking method, when “turned on its head,” had the potential for a solution. Learning of our latest progress on a Friday, Mac had the idea to invert the process, called his close friend, Dick Kershner, and over that first weekend designed the essentials of the complete Transit Navigation System: multiple polar orbiting satellites radiating two ultrastable frequencies encoded with their orbit parameters, a satellite tracking system receiving these same two frequencies to solve the “direct problem,” and an injection station to transmit the resulting orbit parameters to each satellite, which would continue to orbit the Earth so that submarines with navigation receivers/computers could determine submarine position about once an hour anywhere on Earth.

The “Transit Navigation System” referenced above was the first system in the evolutionary process that led to the GPS we have today. 

The Polaris Missile (Photo Credit: US Naval Institute)

In the history of spending by a government on a system meant for military purposes, there has probably never been an investment that returned so much back to the country and, indeed, the world. The market for GPS-enabled products is expected to be around $130 Billion in the next five years. The lives and frustration saved (remember printing maps from or using a Rand McNally street map?) are incalculable. Perhaps the only downside of GPS - my children have no freaking clue how to navigate without it. The next time you are using a GPS device, think of how two guys with boundless curiosity, the Soviet launch of Sputnik, and a man who had to help a submarine know where it was all came together to get you from point A to point B. 

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