The GPS system was started by the U.S. Department of Defense in 1973, with the first prototype spacecraft launched in 1978 and the full constellation of 24 satellites operational in 1993.
Originally limited to use by the United States military, civilian use was allowed from the 1980s.
Advances in technology and new demands on the existing system have now led to efforts to modernize the GPS and implement the next generation of GPS Block IIIA satellites and Next Generation Operational Control System (OCX).
Announcements from Vice President Al Gore and the White House in 1998 initiated these changes. In 2000, the U.S. Congress authorized the modernization effort, GPS III. During the 1990s, GPS quality was degraded by the United States government in a program called “Selective Availability”; this was discontinued in May 2000 by a law signed by President Bill Clinton.
What is GPS system?
GPS or Global Positioning System is a satellite navigation system that furnishes location and time information in all climate conditions to the user. GPS is used for navigation in planes, ships, cars and trucks also.
The system gives critical abilities to military and civilian users around the globe. GPS provides continuous real time, 3-dimensional positioning, navigation and timing worldwide.
How does GPS System Work?
The GPS system consists of three segments:
1) The space segment: the GPS satellites
2) The control system, operated by the U.S. military,
3) The user segment, which includes both military and civilian users and their GPS equipment.
· Space Segment:
The space segment is the number of satellites in the constellation. It comprises of 29 satellites circling the earth every 12 hours at 12,000 miles in altitude.
The function of the space segment is utilized to route/navigation signals and to store and re transmit the route/navigation message sent by the control segment. These transmissions are controlled by highly stable atomic clocks on the satellites.
· Control Segment:
The control segment comprises of a master control station and five monitor stations outfitted with atomic clocks that are spread around the globe.
The five monitor stations monitor the GPS satellite signals and then send that qualified information to the master control station where abnormalities are revised and sent back to the GPS satellites through ground antennas. Control segment also referred as monitor station.
· User Segment:
The user segment comprises of the GPS receiver, which receives the signals from the GPS satellites and determine how far away it is from each satellite. Mainly this segment is used for the U.S military, missile guidance systems, civilian applications for GPS in almost every field. Most of the civilian uses this from survey to transportation to natural resources and from there to agriculture purpose and mapping too.
GPS is used on some incidents in several ways, such as:
- To determine position locations; for example, you need to radio a helicopter pilot the coordinates of your position location so the pilot can pick you up.
- To navigate from one location to another; for example, you need to travel from a lookout to the fire perimeter.
- To create digitized maps; for example, you are assigned to plot the fire perimeter and hot spots.
- To determine distance between two different points.
3 Advantages of GPS:
- GPS satellite based navigation system is an important tool for military, civil and commercial users
- Vehicle tracking systems GPS-based navigation systems can provide us with turn by turn directions
- Very high speed.
2 Disadvantages of GPS:
- GPS satellite signals are too weak when compared to phone signals, so it doesn’t work as well indoors, underwater, under trees, etc.
- The highest accuracy requires line-of-sight from the receiver to the satellite; this is why GPS doesn’t work very well in an urban environment.