GPS or the Global Positioning System an Overview
The GPS can be used for determining someone else"s definite location that provides a highly accurate time reference almost anywhere on Earth. The accuracy of the GPS signal itself is about 5 meters (16 ft) as of 2005 and has steadily improved over the last 15 years. Using differential GPS and other error-correcting techniques, the accuracy can be improved to about 1 cm (.4 in) over short distances.This system was made by and is controlled by the United States Department of Defense and can be used by anyone, with no charge.
The GPS is a satellite-based navigation system made up of a 24-satellite network placed into orbit by the U.S. Department of Defense. The system was first intended for military application. It was in the 1980s, when the government made the system accessible for civilian use.
GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.
The GPS system is divided into three segments: the space, control and the user. The space segment includes the GPS satellite constellation. While the control segment comprises the ground stations around the world that are in charge for monitoring the flight paths of the GPS satellites. And the user segment consists of GPS receivers used for both military and civilian applications.
A GPS receiver decodes time signal transmissions from multiple satellites and calculates its position by trilateration.
The expense of maintaining this system is an estimated amount of US$400 million per year, including the replacement of aging satellites. The first GPS satellite was launched in February 1978, and the most recent launch was in September 2005. The oldest GPS satellite still in operation was launched in February 1989.
Below is a list some other interesting facts about the GPS satellites. The first GPS satellite was launched in 1978.
ð€×   A full constellation of 24 satellites was achieved in 1994.
ð€×   Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.
ð€×   A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended.
ð€×   Transmitter power is only 50 watts or less.
Wondering how it works?
GPS satellites circle the earth twice a day in a very accurate orbit and broadcast signal information to earth. GPS receivers take this information and use triangulation to calculate the user"s exact location. Basically, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user"s position and display it on the unit"s electronic map.
A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position, the latitude and the longitude and then track movement. With four or more satellites in view, the receiver can determine the user"s 3D position (latitude, longitude and altitude). Once the user"s position has been determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more.