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Everything You Need to Know About
Satellite Navigation (GPS)
GPS Explained.
In a nutshell, the Global Positioning
System (GPS) is a space-based navigation system, consisting
of 24 satellites orbiting about 11,000 miles above the
earth. The system is maintained by the US Department
of Defense. A GPS receiver will show you your position,
velocity, direction and time anywhere on the planet.
There are no fees associated with using the signal.
History.
In ancient times, navigation was a difficult
and less than exact science. Sailors guided themselves
using a compass and the stars. A good navigator who
could get you within a few miles of your destination,
was worth his weight in gold. Bad ones, who got lost,
were often executed. In the 17th century accurate time
keeping was added to the equation and navigation became
more accurate but there was still a long way to go.
Fast forward to the 1960s. In the height
of the cold war, scientists were looking for a better
and more precise way to guide ICBMs. After years of
development and testing, GPS was born. On Feb. 22, 1978,
the first Navstar Global Positioning System satellite
was launched from Vandenberg Air Force Base, California.
It was the first of four GPS satellites to be launched
that year.
It took 16 years for the system to become
fully operational with 24 satellites (and some back-ups).
Each satellite weighs about 2,000 pounds and is about
17 feet across with the solar panels extended. The satellites
come equipped with an atomic clock, accurate to within
10-billionths of a second, and a radio transmitter of
about 50 watts. They are solar powered and have a battery
backup for the times when the sun is eclipsed.
How It Works.
The satellites (SVs) transmit a signal
using their own unique ID code, ephemeris data and almanac
data. The ephemeris data contains information about
the position of the satellite, along with the current
date and time. This part of the signal is essential
for determining a position. The almanac data indicates
where all the SVs are supposed to be in orbit at that
given moment. This information is constantly updated
and synchronized by land stations throughout the globe.
The GPS receiver takes this information
and, making dozens of calculations per second, finds
your position. The receiver determines how long it takes
the signal to get from space and then can determine
a “sphere” where it is located. The point
at which the spheres intersect is the location.
The Future
The GPS industry is still very much in
its childhood. Engineers and scientists are working
to make GPS navigation even better. Using corrections
from Ground stations (see DGPS and WAAS Explained),
GPS receivers are becoming more accurate. The Department
of Defense is working on systems with stronger signals
that can penetrate walls and will resist an enemy’s
ability “jam” the signal.
Additionally, industry leaders like Garmin
and Magellan are working to make smaller receivers that
have greater functionality. Look for more integration
with devices like the Garmin Rino, which combines a
GPS and a radio, or the Navtalk GMS cell phone. And
look for other manufacturers to emerge with new and
unique uses for the Global Positioning System.
Who knows? In the future your car may
drive itself guided by the satellites!
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