About this Article
Written by: Adam Goetsch
Written on: May 2nd, 2005
Tags: communication, security & defense
Thumbnail by: GDK/Wikimedia Commons
About the Author
Adam Goetsch was a senior from Sammamish, Washington in the fall of 2005. He was majoring in Computer Science at the University of Southern California.
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Volume VII Issue I > The Evolution of GPS
The Global Positioning System (GPS) is rapidly becoming an integral part of our everyday lives. The system, created by the United States Department of Defense in 1973, has gone through many changes since its introduction to the public in 1995. GPS uses the concept of trilateration to provide your location, but relies on Differential GPS and atomic clocks to vastly improve the accuracy. With such precision, GPS is being used in myriad applications including personal navigation and military missile guidance systems. And as this technology continues to decrease in price, GPS will likely be used in increasingly more exciting applications such as digital file security. First, though, the U.S Government must address the issue of privacy as it pertains to GPS.


We've all been there: you are cruising down the street, desperately trying to peer out your window and read the street numbers. Did you make a wrong turn? Soon, you come to a realization that you have been dreading: you're lost. In the past, this was a very common occurrence. But since the advent of the Global Positioning System (GPS), an increasing number of people are able to easily navigate to their desired destination. GPS technology allows users to pinpoint their exact location through a small GPS receiver. Today, GPS receivers are found in cars, boats, planes, laptop computers, tractors, and countless other applications.
GDK/Wikimedia Commons
In order to fully appreciate the importance of this technology, it is important to understand how GPS works, its current applications, potential problems associated with GPS, and expected future applications. First, however, one must understand the motivations behind the creation of GPS.


In 1973, the idea of a Global Positioning System, initially dubbed NAVSTAR, was developed by the United States Department of Defense. Originally, the technology was intended solely for military personnel and transportation units to obtain their location [1]. Five years later, in 1978, the first four GPS satellites were launched into space by the U.S. Department of Defense. GPS did not reach full operational capacity until July 17, 1995, because a minimum of 24 satellites are needed to provide full coverage.
Before the commercial release of GPS, the Department of Defense announced that two different GPS services would be developed: Standard Positioning Service (SPS) and Precise Positioning Service (PPS). SPS, eventually activated eight years later, was to be released to the public while PPS was to be reserved for use by the U.S military. The essential difference between SPS and PPS was that a deliberate random error was used in SPS to prevent civilians from obtaining exact coordinates through a technique called Selective Availability (SA) [2]. SA degraded the signal by roughly 100 meters by slightly altering the satellites' clocks [3]. The DOD felt that this change was necessary to protect the security interests of the U.S. and its allies by denying the full capabilities of GPS to potential enemies.
President Bill Clinton ended the SA service on May 1, 2000. He explained that "worldwide transportation safety, scientific, and commercial interests could best be served by discontinuation of SA" [4]. Because they are still able to selectively deny GPS signals regionally in the case of threatened national security, the DOD felt that SA could be eliminated without making the U.S or its allies vulnerable. While SPS is still not as precise as PPS, the termination of SA increased its accuracy fivefold.