Does it work in reverse?

On a Friday in 1957, what was then the United Soviet Socialist Republic (USSR) surprised the world and successfully delivered Sputnik 1 into orbit above the earth.

It was the world’s first artificial satellite and it startled America into the Space Race.

The unexpected launch also got William H. Guier and George C. Weiffenbach thinking.

They were two American theoretical physicists from the John Hopkin’s Applied Physics Laboratory who, on the Monday following the launch were surprised to learn that no one had come in over the weekend to try and receive the radio signal that Sputnik was broadcasting.

Not least to prove that the thing was actually up there: fake news was not invented with social media!

So they set to work and before the end of Tuesday, they were ‘listening’ to a man-made scientific first.

In a lesson to politicians, George Weiffenbach described it as the “marvellous achievement of the Russians.”

For the next three months, they (and amateur radio operators all over the world) continued to track Sputnik as it encircled the planet.

Bill and George combined their mathematical skill with some hours on the brand new Univac 1200F digital computer, to show that they could roughly predict the satellite’s orbit using only this received signal.

In March 1958 their boss, Frank McClure (known to all as ‘Mac’) asked them if they could invert their solution?

In other words, if they knew the position of the satellite could they locate the receiving station?

At the time, Mac was trying to find a way of accurately locating Polaris submarines and he recognised a possible solution in George and Bill’s work.

Once the question had been asked, the pieces quickly fell into place.

The team calculated that they could work this the other way around and that satellites emitting radio signals could be used to locate receivers on the surface of Earth

Before too long the Polaris Doppler navigation system wasup and operational.

Today, its most famous descendent – the Global Positioning System – is fundamental to the lives of nearly everyone on Earth.