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A pathfinder in outer space

Thanks to a laser beam that reached the surface of the moon in 1969, ships at sea and cars on the road are safely reaching their destinations. The ubiquitous global positioning system (GPS) that is part of every navigation system was made possible by the moon landing. How so?

Goddard
Source: NASA

The road in front of us is dark, and we passed the last road sign ten minutes ago. The light from our headlights only reaches about 50 meters ahead. In the past, this would have been the moment when panic would set in; when we would desperately look at the crumpled map one last time and begrudgingly admit to ourselves that we were lost. But not anymore. Now we just follow the voice from our navigation system. “In 500 meters, turn left.” No problem.

Navigation systems lead us safely to our destination in part because of a technology that was first tested on the moon. The Apollo 11 crew left behind more than just footprints on the moon in 1969; they also left a laser reflector. This reflector still helps determine the exact distance between Earth and the moon. It consists of an array of 100 quartz glass prisms made by Heraeus. NASA selected this special glass because of its durability and extreme purity. To measure distances, a laser beam is focused on the reflector, and then the time it takes for the light to return to Earth is measured.

Satellite
Source: NASA

The exact position of the satellites – determined with laser beams

It was a real sensation when this laser beam returned to Earth in 1969 – and a starting signal. This laser experiment soon developed into a standard tool in satellite technology. To optimize the use of satellites it’s important to know their exact position in space. And this is made possible with the help of a laser retroreflector that are being aimed at from ground stations. So many satellites, even those, that don’t have anything to do with navigating our cars, have a retroreflector on board today. The most important component in those reflectors is the same robust fused silica by Heraeus that is built into the reflector on the Moon. Many satellite missions like for example of the Earth observation satellites JASON of NASA are only made possible thanks to these reflectors.

The Global Positioning System (GPS) as we know it today was developed by the US Department of Defense in the 1970s, shortly after the original moon landing. It helps determine a person’s or vehicle’s exact position – wherever they might be. GPS functions according to an ingeniously simple principle. More than 30 satellites are orbiting the Earth and sending out radio signals, which are received by our car navigation system or the cell phone in our pocket. These devices need signals from at least four satellites to calculate our location.

Ground stations on Earth repeatedly aim laser beams at the GPS satellites. The beam of light hits a reflector the size of a postage stamp that is located on the exterior shell of the satellite. The light speeds from the satellite back to Earth; the time this takes indicates the satellite’s exact position. And that functions so well that more and more satellites are being outfitted with retroreflectors to enable increasingly precise navigation here on Earth – regardless of whether we are on a ship out at sea, walking in the woods, or driving a car in the dark.

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