GPS receiver uses signals from satellites to pinpoint its exact location on Earth, any time, anywhere. Find out how the Global Positioning System lets you find your way around the globe.

Essay by Dylan18560University, Bachelor'sA+, March 2005

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Final Report

Engineering 100

GPS Systems

For years our ancestors having been relying on the stars to cordinate their direction and position when traveling. Some of the greatest explorers of our time, Leif Ericson, Marco Polo, Prince Henry, Christopher Columbus, Amerigo Vespucci, and Vasco da Gama all had to rely on the stars to calculate their positions or the direction they were traveling using two important principles:

altitude (is the angle up from the horizon). Zero degrees altitude means exactly on your local horizon, and 90 degrees is straight up.

azimuth (is the angle along the horizon). Zero degrees corresponds to North, and increasing clockwise. 90 degrees is East, 180 degrees is South, and 270 degrees is West.

Using these two angles, one can cordinate your own position. Today, things are different a little bit easier. With a Garmin GPS handheld device, 4 AAA batteries you can instantly track your position.

Until about a twenty years ago, GPS existed in the realm of high-tech military thrillers. Fictional spies would tote hand-held units that precisely displayed their locations anywhere on earth.

Reality today is that for the price of a $100, you can too. The GPS is based on 24 orbiting satellites that broadcast a precise data signal that allow GPS receivers to locate themselves anywhere on the planet. A receiver can calculate its position (latitude and longitude), altitude, velocity, heading, and precise time of day.

The 24 satellites have a staggered orbit designed so four satellites will be visible from any location on earth 95 percent of the time.

Each satellite broadcasts a repeating message (psydo code) indicating the position and orbital parameters of itself and other satellites, and precise atomic time. The information is encrypted into a signal and sent to earth.

A small bit of algebra envolving...