The Global Positioning System: Assessing National Policies

By Scott Pace; Gerald Frost et al. | Go to book overview
Save to active project

Chapter One

The Global Positioning System (GPS) is a U.S. military space system operated by the U.S. Air Force. It consists of three segments: The space segment of GPS is a constellation of 24 satellites that broadcast precise time signals. When the satellites are in view of a suitable GPS receiver, these signals can be used to aid position-location, navigation, and precision timing. The control segment consists of a control center and access to overseas command stations, and the user segment includes GPS receivers and associated equipment. The GPS space and ground segments were developed over two decades at the cost of more than $10 billion.1 The purpose of this massive effort was to provide a highly accurate, secure, reliable way for U.S. forces to navigate anywhere in the world, without having to reveal themselves through radio transmissions.

GPS satellites transmit two different signals: the Precision or P-code and the Coarse Acquisition or C/A-code. The P-code is designed for authorized military users and provides what is called the Precise Positioning Service (PPS). To ensure that unauthorized users do not acquire the P-code, the United States can implement an encryption segment on the P-code called anti-spoofing (AS). The C/A-code is designed for use by nonmilitary users and provides what is called the Standard Positioning Service (SPS). The C/A-code is less accurate and easier to jam than the P-code. It is also easier to acquire, so military receivers first track the C/A-code and then transfer to the P-code. The U.S. military can degrade the accuracy of the C/A-code by implementing a technique called selective availability (SA). SA thus controls the level of accuracy available to all users of the Standard Positioning Service.

GPS had its wartime debut during the Persian Gulf War and was one of the most prominent military technologies of the war. Although the entire constellation of satellites was not yet complete, GPS signals were available for many hours a

Senator James Exon, "GPS's Limitless Potential", April 30, 1993 speech on the floor of the U.S. Senate, reprinted in Space News, May 31-June 6,1993, p. 15. The ground segment consists of the master control station and worldwide monitoring stations.


Notes for this page

Add a new note
If you are trying to select text to create highlights or citations, remember that you must now click or tap on the first word, and then click or tap on the last word.
Loading One moment ...
Project items
Cite this page

Cited page

Citations are available only to our active members.
Sign up now to cite pages or passages in MLA, APA and Chicago citation styles.

Cited page

Bookmark this page
The Global Positioning System: Assessing National Policies


Text size Smaller Larger
Search within

Search within this book

Look up

Look up a word

  • Dictionary
  • Thesaurus
Please submit a word or phrase above.
Print this page

Print this page

Why can't I print more than one page at a time?

While we understand printed pages are helpful to our users, this limitation is necessary to help protect our publishers' copyrighted material and prevent its unlawful distribution. We are sorry for any inconvenience.
Full screen
/ 368

matching results for page

Cited passage

Citations are available only to our active members.
Sign up now to cite pages or passages in MLA, APA and Chicago citation styles.

Cited passage

Welcome to the new Questia Reader

The Questia Reader has been updated to provide you with an even better online reading experience.  It is now 100% Responsive, which means you can read our books and articles on any sized device you wish.  All of your favorite tools like notes, highlights, and citations are still here, but the way you select text has been updated to be easier to use, especially on touchscreen devices.  Here's how:

1. Click or tap the first word you want to select.
2. Click or tap the last word you want to select.

OK, got it!

Thanks for trying Questia!

Please continue trying out our research tools, but please note, full functionality is available only to our active members.

Your work will be lost once you leave this Web page.

For full access in an ad-free environment, sign up now for a FREE, 1-day trial.

Already a member? Log in now.

Are you sure you want to delete this highlight?