Gps

If you happen to be in a quiet place while you’re reading these words—I mean a really quiet place—cast your eyes heavenward for a moment and listen very intently. Hear it? That very gently swishing sound you hear is being made by thirty satellites moving silently through space, circling our globe more than 12,000 miles above your head.

Okay, they wouldn’t really make a swishing sound in the vacuum of space. But it’s the best way I know to describe the amazing fact that these satellites, 24x7x365 are moving in their steady circles. You and I didn’t put them there, and you may not have even known about them—or thought about them if you did know. But more and more, the presence of these satellites is impacting how you and I live.

These satellites are part of the nearly thirty-year-old Global Positioning System. You’ve probably heard of “GPS,” and may even be an experienced user. GPS technology is being integrated further and further every day into the fabric of our lives. You may have a car or boat that uses GPS for navigation. Or a GPS unit that fits on your bike, or one that straps on your wrist. If you’re a pilot, you’re very familiar with GPS; and if you’re a farmer, your computer-guided tractor may use the GPS system to plow perfectly-straight furrows, acre after acre. Some cell phones are equipped with GPS technology. (Think of the life-saving benefits of such a phone when it comes to search-and-rescue.) Map-makers, surveyors, members of the military—the list goes on and on. You and I may not think much about what makes GPS work, but we should be thankful for it.

GPS was originally developed by the Department of Defense for military purposes and is today maintained by the U. S. Air Force at an annual cost of $750 million. The satellites’ orbits are arranged so that at any given moment, six of the thirty satellites would be visible from any point on earth (if you could actually see them in space). Each of these thirty satellites is constantly sending out signals that are picked up by the other satellites and a GPS receiver on earth (in your car, cell phone, boat, or in your hand as you hike a wilderness trail).

Then, by a technology called trilateration (using some really fancy math), the location of the GPS receiver on earth is instantly calculated and recalculated as the receiver moves—even moving a few feet creates a new calculation and location. Trust me—I can’t conceive of how this works from a mathematical and scientific perspective. I’m only glad that it does. When I am trying to drive in my car somewhere I’ve never been before, I’m grateful for the GPS device that tells me when and where to turn.

Care; Direction; Purpose

Turning Points

August 2007

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