What Are GPS Satellites Used For?

GPS stands for Global Positioning System. It is an elaborate system that uses a number of satellites in orbit to provide our location here on Earth. The system was designed by the United States Department of Defense and originally designated for military applications. It helped US forces stage operations in Operation Desert Storm. Its usage was later extended to civilians.

Satellites

There are 24 GPS satellites in orbit at all times. The satellites travel on six separate orbital paths 20,000 kilometers over Earth's surface. Each satellite completes one full orbit every 12 hours. The design of the orbits was strategically calculated to ensure that anyone using a GPS receiver on Earth's surface is able to have a clear view of at least four satellites at any one time.

Function

Each satellite in the system beams radio wave transmissions down to Earth at regular intervals. The transmissions contain a variety of information including the satellite's orbital location, identification on the individual satellite and the time the transmission was sent. Each satellite uses an atomic clock, which provides a very precise time, down to the nanosecond. The transmissions travel to Earth at the speed of light.

Reception

Every GPS device that we use is a receiver that contains circuitry capable of receiving transmissions from the GPS satellites and deciphering the information contained in the signal. The receiver uses the time stamp from the transmission to calculate distance. Since the transmission was travelling at a known speed (speed of light), the receiver is able to determine the distance to the satellite by gauging how long it took the transmission to reach Earth.

Trilateration

Getting the distance to one satellite will only provide a distance from you to it. One distance is useless in providing your actual location. It takes the distances to three separate satellites to provide a set of coordinates. Four satellites enable the user to get the additional measurement of altitude. The more satellites that are used in the equation, the more accurate the location provided by GPS becomes.

Other Uses

In addition to its use in land, air and sea navigation, GPS has a variety of applications across many disciplines. The GPS system is constantly being applied to new activities and its uses are numerous. Some of the scientific and public uses include providing data on earthquakes, helping to coordinate emergency service efforts and assisting in surveying and building projects.