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GPS: More Than Just a Gadget |
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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.
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