Military, government, and civilian users all over the world rely on GPS for navigation and location positioning, but radio signals have been used for navigation purposes since the 1920s. LORAN (Long Range Aid to Navigation), a position-finding system that measured the time difference of arriving radio signals, was developed during World War II.
The first step to GPS came way back in 1957 when the Russians launched Sputnik, the first satellite to orbit the Earth. Sputnik used a radio transmitter to broadcast telemetry information. Scientists at the Johns Hopkins Applied Physics Lab discovered that the Doppler shift phenomenon applied to the spacecraft — and almost unwittingly struck gold.
A down-to-earth, painless example of the Doppler shift principle is when you stand on a sidewalk and a police car speeds by in hot pursuit of a stolen motorcycle. The pitch of the police siren increases as the car approaches you and then drops sharply as it moves away. American scientists figured out that if they knew the satellite’s precise orbital position, they could accurately locate their exact position on Earth by listening to the pinging sounds and measuring the satellite’s radio signal Doppler shift. Satellites offered some possibilities for a navigation and positioning system, and the U.S. Department of Defense (DoD) explored the concept. By the 1960s, several rudimentary satellitepositioning systems existed. The U.S. Army, Navy, and Air Force were all working on independent versions of radio navigation systems that could provide accurate positioning and allweather, 24-hour coverage. In 1973, the Air Force was selected as the lead organization to consolidate all the military satellite navigation efforts into a single program.
This evolved into the NAVSTAR (Navigation Satellite Timing and Ranging) Global Positioning System, which is the official name for the United States’ GPS program. The U.S. military wasn’t just interested in GPS for navigation. A satellite location system can be used for weapons-system targeting. Smart weapons such as the Tomahawk cruise missile use GPS in their precision guidance systems. GPS, combined with contour-matching radar and digital image-matching optics, makes a Tomahawk an extremely accurate weapon. The possibility of an enemy using GPS against the United States is one reason why civilian GPS receivers are less accurate than their restricteduse military counterparts.
The first NAVSTAR satellite was launched in 1974 to test the concept. By the mid-1980s, more satellites were put in orbit to make the system functional. In 1994, the planned full constellation of 24 satellites was in place. Soon, the military declared the system completely operational. The program has been wildly successful and is still funded through the U.S. DoD.
The first step to GPS came way back in 1957 when the Russians launched Sputnik, the first satellite to orbit the Earth. Sputnik used a radio transmitter to broadcast telemetry information. Scientists at the Johns Hopkins Applied Physics Lab discovered that the Doppler shift phenomenon applied to the spacecraft — and almost unwittingly struck gold.
A down-to-earth, painless example of the Doppler shift principle is when you stand on a sidewalk and a police car speeds by in hot pursuit of a stolen motorcycle. The pitch of the police siren increases as the car approaches you and then drops sharply as it moves away. American scientists figured out that if they knew the satellite’s precise orbital position, they could accurately locate their exact position on Earth by listening to the pinging sounds and measuring the satellite’s radio signal Doppler shift. Satellites offered some possibilities for a navigation and positioning system, and the U.S. Department of Defense (DoD) explored the concept. By the 1960s, several rudimentary satellitepositioning systems existed. The U.S. Army, Navy, and Air Force were all working on independent versions of radio navigation systems that could provide accurate positioning and allweather, 24-hour coverage. In 1973, the Air Force was selected as the lead organization to consolidate all the military satellite navigation efforts into a single program.
This evolved into the NAVSTAR (Navigation Satellite Timing and Ranging) Global Positioning System, which is the official name for the United States’ GPS program. The U.S. military wasn’t just interested in GPS for navigation. A satellite location system can be used for weapons-system targeting. Smart weapons such as the Tomahawk cruise missile use GPS in their precision guidance systems. GPS, combined with contour-matching radar and digital image-matching optics, makes a Tomahawk an extremely accurate weapon. The possibility of an enemy using GPS against the United States is one reason why civilian GPS receivers are less accurate than their restricteduse military counterparts.
The first NAVSTAR satellite was launched in 1974 to test the concept. By the mid-1980s, more satellites were put in orbit to make the system functional. In 1994, the planned full constellation of 24 satellites was in place. Soon, the military declared the system completely operational. The program has been wildly successful and is still funded through the U.S. DoD.
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