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.