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What on Earth is the Global Positioning System?

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GPS is everywhere—on your phone, in your car, even on your wrist—but what the heck even is it and how does it work?

GPS is short for Global Positioning System. It’s a satellite-based navigation system that helps people find their precise location on Earth. 

A seaman recruit  uses a stadimeter sextant looking across sea.
Stadimeter sextant
Seaman Recruit Emily Gideon, from San Antonio, uses a stadimeter sextant to measure the distance to the approaching USS Stethem (DDG 63) from the bridge of the Navy's only forward-deployed aircraft carrier, USS Ronald Reagan (CVN 76). USS Stethem was on approach to conduct a fueling-at-sea with Ronald Reagan. Ronald Reagan, the Carrier Strike Group Five (CSG 5) flagship, is on patrol supporting security and stability in the Indo-Asia-Pacific region. (U.S. Navy photo by Petty Officer 3rd Class Nathan Burke/Released)
Photo By: Navy photo
VIRIN: 161002-N-OI810-004

Before GPS, navigation involved paper maps or very specialized tools like sextants and chronometers. Now, satellites orbiting the Earth 12,000 miles up can guide pizza delivery drivers to your house before the cheese cools.

Back in 1973, the military began looking for a reliable, accurate means of electronic navigation. Existing systems didn’t always work accurately enough for military purposes, and some were vulnerable to an enemy attack.

The difference between Trilateration and Triangulation.
Trilateration versus Triangulation
The difference between Trilateration and Triangulation.
Photo By: Defense Media Activity
VIRIN: 181029-D-ZZ999-013

The system that was developed allowed a GPS receiver to connect to three or more satellites to trilaterate their position, but it was limited to military use until the 1980s. President Ronald Reagan made it available to the world after a Korean airliner was shot down by Soviet fighters when it strayed off course due to navigational errors.

A photo of a service member looking at a GPS device appears on a graphic illustration showing satellites in orbit.
How Your GPS Device Knows Where You Are
How Your GPS Device Knows Where You Are graphic
Photo By: DOD
VIRIN: 200630-D-ZZ999-101

GPS is still owned by the U.S. government and the satellites are operated by the Air Force, though it’s available for use by anyone in the world with a GPS receiver.

Technological advances have improved GPS’ accuracy, and the newest systems will allow a user to pinpoint their position to within less than a foot.

Quick facts:

GPS was developed by the U.S. military, but is free for anyone in the world to use.
The Gulf War was the first time the military used GPS in combat.
Early military ''handheld'' GPS receivers weighed 35 pounds.
The first GPS-enabled cell phones appeared in 2004.
GPS has two levels of service: Standard Positioning Service, available free worldwide, and Precise Positioning Service, which is restricted to U.S. armed forces and federal agencies and to selected allies.
Other countries are developing their own versions of GPS, such as the Russian Global Navigation Satellite System, or GLONASS, and China’s BeiDou Navigation Satellite System.

A U.S. Marine kneeling on the ground positioning a satellite
U.S. Marine with Satellite
A U.S. Marine with 2nd Assault Amphibian Battalion, 2nd Marine Division, establishes communication with Marines on the USS New York located in the Norwegian Sea during an amphibious landing during Exercise Trident Juncture 18, in Alvund, Norway, Oct. 30, 2018. Trident Juncture 18 demonstrates II Marine Expeditionary Force ability to deploy, employ, and redeploy the Marine Air-Ground Task Force while improving interoperability with NATO Allies and partners. (U.S. Marine Corps photo by Cpl. Patrick Osino)
Photo By: Cpl. Patrick Osino
VIRIN: 181030-M-AS512-009C

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