Global Positioning System (GPS)

The Global Positioning System (GPS) is a system of satellites that provides navigation and timing information to military and civilian users worldwide. GPS satellites, in one of six medium earth orbits, circle the earth every 12 hours emitting continuous navigation signals on two different radio frequencies. GPS receiver units acquire the satellite signals and translate them into precise position and timing information.

SFC Dan MacMaster (left) and SGT Julie Munsterman of 323d Maintenance Company confirm their position at a designated waypoint during GPS training, Tobyhanna Army Depot, PA, 2006
SFC Dan MacMaster (left) and SGT Julie Munsterman of 323d Maintenance Company confirm their position using Precision Lightweight GPS Receivers (PLGR) at a designated waypoint during GPS training, Tobyhanna Army Depot, PA, 2006.

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Global Positioning System (GPS)

The Global Positioning System (GPS) is the only utility operating and providing continuous services on a worldwide basis. GPS is also the world's largest military satellite constellation, called Navigation System using Timing And Ranging (NAVSTAR). Dual use (civilian and military) GPS supports military operations, search and rescue, communications, farming, recreation and both military and commercial aviation. GPS also provides precise timing for financial transactions and similar time-dependent applications.

The Global Positioning System (GPS) is fundamentally a military system, operated by the 2nd Space Operations Squadron at Schriever Air Force Base, CO. From the program's inception in the 1970s, the U.S. Department of Defense has been dedicated to successful management of the GPS as both civil and military national information resource. Under DoDís stewardship, GPS has grown to be a global industry.

Diagram of the GPS nominal constellation of 24 satellites in six orbital planes, four satellites in each plane.  Altitude is 13,800 miles (22,200 km) at 55 degree inclination
Diagram of the GPS nominal constellation of 24 satellites in six orbital planes, four satellites in each plane. Altitude is 13,800 miles (22,200 km) at 55 degree inclination.

The first GPS satellite was launched in February 1978 and the first widespread use was in the 1990-1991 Gulf War where GPS was highly useful in the featureless desert. The space component of GPS now consists of a minimum of 24 satellites, each in one of six medium earth orbits. GPS satellites circle the earth every 12 hours emitting continuous time signals on two different L-band frequencies (1575.42 MHz civilian and 1227.60 MHz military). The orbital plan guarantees that at least three satellites are in view of a receiver at any time, anywhere on earth, sufficient to locate the receiver by latitude and longitude. To also fix altitude, a fourth satellite must be in view. The system is managed by a worldwide satellite control network that feeds satellite reference data to 2nd Space Operations Squadron in Colorado.

For military operations, Global Positioning System (GPS) is being integrated into all DoD combat forces, at all levels, from the hand-held receiver carried by the infantryman to the embedded GPS aircraft or naval navigation system. GPS provides precision location determination and navigation support automatically with unprecedented accuracy. GPS is a part of the guidance system in most current and planned precision-guided munitions being acquired by the armed services.

GPS receivers are incorporated into nearly every type of system used by the DoD: aircraft, spacecraft, ground vehicles and ships, providing highly accurate, three-dimensional location information. Such missions as mapping, aerial refueling, rendezvous operations, geodetic surveying, and search and rescue operations have all benefited greatly from the accuracy of GPS.

Global Positioning System (GPS) Security

To prevent the hostile use of GPS against U.S. and allied forces, DoD has implemented a security program known as Navigation Warfare (NAVWAR). The objectives of NAVWAR are:

  • Protect the use of GPS by DoD and allied forces in times of conflict within the theater of operations
  • Prevent the use of GPS by adversary forces
  • Preserve routine GPS service to all outside the theater of operations

In a hostile environment, GPS signals may be jammed or spoofed by the enemy. This has actually been observed when commercial GPS receivers are utilized. Military GPS is encrypted and cannot be easily interfered with on the battlefield. At one time, the civilian GPS signal was purposely degraded to provide a lower quality of service (position accuracy) than that available to the military. However, the use of Differential GPS overcame the inaccuracy and could provide position location within 1-3 meters for all users. For that reason, the U.S. Department of Defense dropped the selective availability feature in 2000.

Global Positioning System (GPS) Equipment

Generations of GPS equipment: the 17 pound AN/PSN-8 backpack receiver (rear left), the ten pound AN/PSN-9 portable, the four pound AN/PSN-10 (front left), the three pound AN/PSN-11 PLGR (second from right), and the one pound AN/PSN-13 DAGR (right)
Generations of GPS equipment: the 17 pound AN/PSN-8 backpack receiver (rear left), the ten pound AN/PSN-9 portable, the four pound AN/PSN-10 (front left), the three pound AN/PSN-11 PLGR (second from right), and the one pound AN/PSN-13 DAGR (right).

This section of Olive-Drab.com has individual pages with photos and information about specific items of U.S. military GPS equipment, listed here:

Find More Information on the Internet

There are many fine websites that have additional information on this topic, too many to list here and too many to keep up with as they come and go. Use this Google web search form to get an up to date report of what's out there.

For good results, try entering this: gps satellite. Then click the Search button.

Especially recommended: USNO NAVSTAR Global Positioning System. This link is a video explaining military and civilian GPS systems and the risks to warfighters using civilian models.