GPS is not an app on your phone. GPS stands for Global Positioning System. It comprises a minimum of 24 satellites (currently 31) that orbit the earth at an altitude of 20,200 kilometers (12,550 miles). The system is a utility that provides positioning, navigation, and timing services. It is owned by the U.S. government and operated by the U.S. Air Force. Your phone is just one type of signal receiver.
Here's how GPS works:
Each satellite occupies a position in one of six different orbital planes and orbits the earth every 12 hours. Their precise placement ensures that at least four are visible to virtually every spot on the planet at every moment of every day. As the satellites orbit, they continually send out radio signals, broadcasting information about their locations and the precise time. These signals serve as beacons. The radio signals travel through space at the speed of light. Although the time it takes a signal to reach the earth's surface is just a tiny fraction of a second, the time varies in miniscule amounts based on how far away a specific satellite is from an individual receiver. When a GPS device receives signals from multiple satellites and notes the exact time the signals arrive, it employs the principles of geometry to pinpoint its location on Earth's surface. The map software used by the receiving device is not actually part of the GPS system, but adding map information helps provide the turn-by-turn directions that have become ubiquitous for today's travelers.
The origins of modern GPS technology can be found in the 1960s when satellites were first employed to track submarines. In 1978, the U.S. Department of Defense launched the first NAVSTAR (Navigation System with Timing and Ranging) satellite. By 1995, 24 radionavigation satellites were in place and fully operational. The most recently deployed GPS satellite was launched on February 5, 2016, and it became available to the system on March 9, 2016. The GPS satellites represent a mix of older and newer technologies. When aging GPS satellites need to be replaced, the Air Force is responsible for launching new ones. Some decommissioned satellites are maintained in orbit in case a need arises to reactivate them.
In addition to location information for travelers, GPS provides global navigation and time services. The precise time information provided by GPS enables accurate time stamping for financial transactions and the global synchronization of events. Navigation services aid search and rescue operations, facilitate disaster relief and emergency responses, help guide civilian and military aircraft (and even some spacecraft), and enable precision agricultural methods that result in increased crop yields. For ships at sea, GPS stands as a virtual network of lighthouses in the sky.
Current GPS satellites provide two different levels of service: Precise Positioning Service (PPS), which is available to U.S. and selected allied agencies and armed forces, and Standard Positioning Service, which is freely available to users around the world. Civilian GPS accuracy with a high-quality receiver is 3.5 meters or better, and often within one meter (although accuracy can be compromised by atmospheric effects, structural blockages, signals bouncing off obstacles, and the quality of the receiver). GPS is operated and controlled by the U.S. Air Force's 50th Space Wing, which is located at Schriever Air Force Base in Colorado.
This article, along with additional images and resources, originally appeared in the May 2016 issue of Observations: A Pier Press® Newsletter. If you're not already a subscriber, click here to sign up. It's free.