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A little light reading on GPS info

Oct 27, 2021
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The U.S. Department of Defense(in the late 70's/early 80's) began work on a revised system to improve the accuracy of an earlier project that was designed for "tracking and positioning" purposes. The improved system became known as The Global Positioning System(GPS) that we use today. Many satellites have since been retired and replaced by more advanced satellites and the system is still going strong. But, it wasn't always smooth sailing for the GPS project. The GPS service was first made available for civilians in 1983, but, for national security reasons, the U.S. Military decided to scramble the signal, making it inaccurate to be reliable for consumer companies. The practice, was known as "selective availability," and was aimed at preventing military use of our GPS by foreign enemies.
It wasn't until President Clinton's decision to turn off the GPS interference signal and make GPS available to commercial and public users which in-turn, helped make consumer-grade mobile navigation systems possible. Today we can drive our cars aided by directions and fly are drones with great accuracy because of that decision. But, our GPS system was not alone for too long. The EU(Galileo) and Russia(GLONASS), both luanched systems for positioning purposes. On any given day the US GPS has a minimum of 24 satellites available for use with others just floating around up there.
When I bought my first Q500+ I read somewhere that Yuneec drones were capable of using satellites from the US, EU, and Russia. I assume that they still make drones that are able to use systems from the Big 3.

A few facts about GPS:
Three satellites are needed to ascertain the position of a GPS receiver.
It takes 24 satellites and several backup satellites orbiting the Earth at a height of more than 20,000 kilometers, to ensure that three satellites are available anywhere in the world and at any time.
Satellites transmit an uninterrupted signal detailing their current location and time, and it's up to the GPS receiver to handle the signal delay with the help of an integrated clock to calculate its own position and speed.
Using distance measurements from three points, known as triangulation, exact positions are determined. The signal from the first satellite determines the receiver's degree of longitude; the second identifies the degree of latitude. As the receiver's integrated clock is not accurate enough to measure the exact signal delays, the clock error is calculated using a third satellite and thus identifying the exact position.

(Removed by moderator - rule 13)

Edited Nov 23, 2022...
In the last paragraph above, I used the word "triangulation" this is not correct and it should be trilateration.
is based upon distances rather than the intersection of lines based on angles.
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