2. How GPS Works

The idea and history of the Global Positioning System (GPS) can be traced back to 1957 when scientists from the Massachusetts Institute of Technology found out that the position of the Russian Sputnik satellite could be tracked from the earth by following the strength of its radio signal. Since then, researchers and the US government have been working on a way to use satellites for error-proof determination of location and navigation capability.

The first GPS system was developed in the early 1960s and operated by the U.S. Department of Defense (DOD). By a presidential directive, it was decided in 1966 to move the system's management from the DOD to the Interagency GPS Executive Board (IGEB), which was overseen by Department Transportation and the DOD to ensure that GPS could meet the requirements for military as well as civil use.

The first operational GPS satellite dates back to 1978. The world's GPS network today consists of 24 satellites with the last unit placed in orbit in 1995. The satellites are positioned in six earth-centered orbital planes with four operation satellites and one open satellite slot in each region for a total capacity of 30 satellites. This organization allows anyone on the planet with a clear view to the sky to theoretically see at least four and a maximum of eight satellites at any given time.

The world surrounded by 24 GPS satellites. Image credit: U.S. Department of the Interior, U.S. Geological Survey

The satellites are overseen by the Master Control Station (MCS) located at the Schriever Air Force Base near Colorado Springs, Colorado. The US Air Force continuously tracks the position of the satellites from island locations in Ascension Island, Diego Garcia, Kwajalein and Hawaii; Cape Canaveral Kennedy Space Center in Florida and Colorado Springs, Col.

Users around the world are able to use devices that detect signals broadcasted to enable GPS-based navigation. The signals can be used to determine, location, speed and time. To detect the satellites' signals, users need so-called GPS receivers that capture the signals and translate them into usable navigation data.

GPS receivers always require a simultaneous connection (and therefore a clear view to the sky) to four satellites to be able to calculate the three dimensions of position (latitude, longitude and altitude). In order to pinpoint their current location, GPS receivers measure their distance to a group of four satellites. GPS receivers then provide location information with an error margin of about 15 ft. (five meters).

We will not go into more detail on how GPS calculates positions, but if you are interested we recommend resources such as Beaglesoft Software's Website to learn more about this technology. Needless to say, there are many other pages about GPS available on the Web, which can easily be found with Google.com.