GPS (Global Positioning System) was funded, developed and controlled by the US Department and Defense. Now GPS has become an important aid to navigation arount the world.
GPS send specially coded signals to satellite. Now a days, our cell phone not for only conversation. It has many features like mp3 player, digital camera and video camera and many more features. But now, GPS feature will soon be added to this list, and GPS has the capability of tracking any cell phone user.
Capability of tracking a cell phone, user can easily track anyone in emergency situation like a car accident, or any other case, where every minute may be a matter of life or death. In situation like this, the GPS system will tell you the exact location of the road accident, so that emergency service to be quickly dispatched.
How GPS Works?
GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use trilateration. to calculate the user’s exact location. This operation is based on a simple mathematical principle called trilateration. The principle behind GPS is the measurement of distance (or “range”) between the satellites and the receiver. The satellites tell us exact location where they are in their orbits by broadcasting data and the receiver uses to compute their positions. The GPS receiver processes the satellite range measurements and produces its position. A GPS receiver’s job is to locate four or more of these satellites, figure out the distance to each, and use this information to deduce its own location.
GPS uses a system of coordinates called WGS 84, which stands for World Geodetic System 1984. It allows surveyors all around the world to produce maps like the ones you see in school, all with a common reference frame for the lines of latitude and longitude that locate places and things. Likewise, GPS uses time from the United States Naval Observatory in Washington, D.C., to synchronize all the timing elements of the GPS system, much like Harrison’s chronometer was synchronized to the time at Greenwich.
Now you have clear picture of the GPS system, how does it work. You know that it consists of satellites whose paths are monitored by ground stations. Each satellite generates radio signals that allow a receiver to estimate the satellite location and distance between the satellite and the receiver. The receiver uses the measurements to calculate where on or above Earth the user is located.
Here are some other interesting facts about the GPS satellites (also called NAVSTAR, the official U.S. Department of Defense name for GPS):
- The first GPS satellite was launched in 1978.
- A full constellation of 24 satellites was achieved in 1994.
- Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.
- A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended.
- Transmitter power is only 50 watts or less.