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I want to cross post a dumb thing i posted on a gbs thread about GPS satellites because theyre cool and i've worked on GPS related poo poo on and off./ A key component of GPS satellites is that they know the UTC time and their own position in space very accurately, and that time is periodically fed to them by ground stations equipped with atomic clocks. A gps receiver determines its position by a process called trilateration, which is where you time how long it takes for a signal to reach you from three known points - this gives you the intersection of three spherical surfaces which is two points in 3D space, and you can easily decide which of those two is where you are because one will be on the earth's surface and the other will be out in space somewhere.  How do you know how long the signals took to reach you? You have the speed - they are radio signals are travelling at (roughly) the speed of light - and can determine the time as the signals are sent out exactly every millisecond relative to the UTC clock, so you can measure how much the signal is delayed compared to the clock. Your hand-held GPS receiver doesn't have an accurate atomic clock, but it's OK because it can figure out the time given a fourth satellite signal (creating a system of 4 simultaneous equations in 4 variables), and can solve for your xyz position in cartesian coordinates centred on earth's core. The GPS satellites are in medium earth orbit, about 12 thousand miles out - they need to be far out in space so that the radio signal takes long enough to get to earth that you can measure the time taken - but the interesting thing about GPS is that the principle of trilateration is not at all limited to earth's surface. It would work just fine out in space too, or more to the point in the upper atmosphere where an ICBM could track its position, etc. GPS devices are all manufactured with a hard limit on the altitude that they will work at so you can't use them for nukes Are there any other GPS/GNSS goons in the house??
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Feb 24, 2021 17:03
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| # ¿ Apr 24, 2024 13:13 |
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