Gps: More Than Just A Gadget

Whenever we hear the term "GPS", what would probably come to our minds is a digital device with maps and other features that tells us our exact location on Earth. But did you know that such a device is just one part of GPS? The device is called a GPS receiver, and while it is certainly an important GPS device, it is but a part of a very large and complicated system that allows us to measure our exact location on earth.

The three-lettered abbreviation "GPS" stands for Global Positioning System. It is a satellite-based navigation system that has the ability to measure an object's exact location on earth. The United States' Department of Defense (DOD) developed the system and officially called it the NAVSTAR GPS (Navigation Signal Timing and Ranging Global Positioning System). It was intended to be used for only military operations but has been available for civilian use since the 1980s.

The Global Positioning System is an enormous and complex system that may be divided into three segments: space, control, and user. The "control" segment refers to the various stations on Earth that sustain and control the system. The "space" segment of the GPS refers to its system of satellites that transmits the signals used for location identification. The "user" segment refers to the GPS receivers--the actual unit that we often mistakenly think of as the system.

CONTROL

The "control" segment of the GPS refers to the various ground stations run by the US Department of Defense that controls the numerous aspects of the system. Specifically, these stations oversee the flight of the GPS satellites, synchronize the satellite's onboard atomic clocks, and upload the data to be transmitted by the satellites.

SPACE

The "space" segment of the GPS is a constellation of 27 satellites that orbit Earth 12,600 miles above its surface. 24 of these satellites are in operation while the other three are on standby mode and will be used only if one of the 24 fails. Each of the satellites travels around the earth twice in less than 24 hours, traveling at a speed of approximately 7,000 miles per hour.

Each of the satellites used in the GPS configuration weighs between 3,000 to 4,000 pounds. All of these satellites are solar-powered, but all have backup batteries onboard to be used in the absence of solar power (i.e., solar eclipse). The satellites are also equipped with small rocket boosters to keep them flying on the correct path.

The signals that are transmitted by the GPS satellites are low-powered radio signals. These signals contain three different sets of data--a pseudorandom code, ephemeris data, and almanac data--that are deciphered by the GPS receiver to obtain a precise measure of its location. The pseudorandom code tells the receiver which satellite is broadcasting the signal while the ephemeris data provides information about the satellite's position. Meanwhile, the almanac data contains information like the status of the satellite, current date and time.

USER

The "user" segment of the GPS refers to the GPS receivers, used for either military or civilian purposes. The GPS receiver is essentially an electronic device that picks up the signal transmitted by the satellites and uses the information on those signals to figure out its precise location. Of course, this function is much more complex than a simple summary makes it sound.

The GPS receiver in fact needs two things for it to gauge its location. First, it needs information to tell it the location of at least three GPS satellites. Then, it would need to measure the length between it and each of the three GPS satellites. The first information can be interpreted from the signal transmitted by the satellites while the second set of data can be obtained by measuring the speed at which the signal was received.

ALL-IN-ONE SYSTEM

Combining the control, space, and user segments, we have a Global Positioning System that can reveal our precise location here on earth.

As you can see, the GPS is not solely the GPS receiver alone. It is an immense system, and a very complex one at that. But, because every other part of the system is well maintained by the Department of Defense, we should never have to worry about those parts. All we must do is secure a GPS receiver and, in an instant, we'll receive information about our current location and other landmarks and road conditions that the receiver may want us to know.