The Hottest Gift This Christmas…
is a GPS receiver. I get lost in my driveway and yet I still do not own one of these things. In case you were wondering (you probably weren’t wondering, but I was), here is how the thing works:
When people talk about “a GPS,” they usually mean a GPS receiver. The Global Positioning System (GPS) is actually a constellation of 27 Earth-orbiting satellites (24 in operation and three extras in case one fails). The U.S. military developed and implemented this satellite network as a military navigation system, but soon opened it up to everybody else.
Each of these 3,000- to 4,000-pound solar-powered satellites circles the globe at about 12,000 miles (19,300 km), making two complete rotations every day. The orbits are arranged so that at any time, anywhere on Earth, there are at least four satellites “visible” in the sky.
A GPS receiver’s job is to locate four or more of these satellites, figure out the distance to each, and use this information to deduce its own location. This operation is based on a simple mathematical principle called trilateration.
My simple mind finds that fascinating.
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Posted By Derrick Moe | General | |
[…] admin had some great ideas on this topic.You can read a snippet of the post here.The Global Positioning System (GPS) is actually a constellation of 27 Earth-orbiting satellites (24 in operation and three extras in case one fails). The US military developed and implemented this satellite network as a military … […]
Interesting fact: the GPS system was, like the internet (TCP/IP), a Defense Advanced Research Projects Agency (DARPA) program. This was deployed by the Pentagon as the NAVSTAR GPS. It was designed so that signals from at least four satellites would be on the horizon at all times, thereby making it possible to compute the current latitude, longitude and elevation of a GPS receiver anywhere on earth.
NAVSTAR’s reference system is free, but the EU is perturbed because they feel it leaves their forces unduly dependent on a US-based technology, so they have sunk billions into the Galileo Program. The Russians have yet another system, GLONASS. GLONASS has 21 satellites, presumably at higher orbits (sacrificing precision for lines of sight).
James - thanks for the expansion on this topic. I wish I could comprehend just how “busy” the space is above the Earth. I’m sure this system is unbelievably complex, but the principle of it seems elegantly simple.