01-12-2012, 06:15 PM
GPS: Global Positioning System
gps2.ppt (Size: 1.77 MB / Downloads: 33)
What is GPS?
GPS is the Global Positioning system which is used to located the position of any person, vehicle or device such that where is that particular device is present etc.
Developed by the Dept. of Defense
$12 billion system
Began construction in mid ’70s
Developed for military operations, but with a provision for civilian use
Consists of 24 (28) high orbit satellites sending out coded radio signals that are picked up by receivers that calculate position
How does GPS work?
GPS is based on satellite ranging
24+ satellites orbit 11,000 miles overhead
Each satellite orbits the earth once every 12 hours
Four satellites are required by the receiver for an exact position
Usually with 5 to 8 SVs visible at any time
(SVs= Space Vehicles)
Precision timing
Each satellite is equipped with an atomic clock, accurate timing is key
Receiver clocks don’t have to be perfect because a trigonometry trick can cancel out receiver clock errors
In reality 3 satellites can give a position (narrows it down to 2 points and the erroneous point is discarded)
The fourth satellite allows for correction of the receiver’s clock
GPS Satellites
NAVSTAR (NAVigation Satellite Timing And Ranging)
Rockwell International
Orbit is 10,900 nautical miles above Earth
Satellites weigh 1900 lbs
17 ft with solar panels extended
12 hour orbital period
Six orbital planes with 4 SVs in each plane
Life span 7.5 years
24+ satellites at any given time (only 17 are required)