In December of 2016 Galileo first went online in the European Union got its own satellite navigation system. it joins the American GPS and the Russian GLONASS and becoming the third system available around the globe.
Navigation systems have long become a part of our everyday lives they power the world of logistics, orchestrate, commercial aviation and enable your phone to take you anywhere in the world. But looking at the history of these systems it’s clear that the motivation behind them was not to take you to your next cappuccino but instead what always pushes technology forward. War – especially if it’s cold – when the Soviet Union launched Sputnik 1 into space in 1957 they became the first nation put a man-made satellite into orbit that of course annoyed the Americans but more importantly it marked the beginning of satellites. A radio in space that constantly orbits the earth and can be used for communication or spying navigation this is especially important if you have things that really should know where they’re going.
GPS first became operational in 1978 and along with the Russian GLONASS it was one of the two major satellite navigation systems for multiple decades. China has since stepped up its base game as well and plans to expand its regional beta into a global system by 2020 and Europe’s own Galileo just went online and will reach completion and 2019 probably.
Our focus on GPS because it’s the most popular, but all of these systems were more or less the same. GPS is not just one satellite but actually a network of up to 32 satellites orbiting the Earth 20,000 kilometers above ground that way they are always a few above you. These GPS satellites are basically atomic clocks with radio and solar panels constantly sending signals back to earth. Each broadcast contains the current location and the precise time the signal was sent and even though these broadcasts travel at the speed of light it still takes between 50 and 100 milliseconds for them to reach the earth. a GPS receiver listens to all of these signals but because some satellites are further away from you than others, their signals arrive at different times so when satellite A and B send out a signal saying that is exactly 12 o’clock but the signal from satellite A gets to you’re first then you have to be closer to satellite A than B. Your GPS receiver can measure the process time between the two signals and calculate how much closer satellite A is. because the satellites also sent out their current position you not only know where you are in relation to the satellites but where you are exactly at a third satellite and you can get coordinates in a two dimensional space or a map, and with a fourth you can also calculate elevation, and with a system like that you can pinpoint your exact position on earth with an accuracy of up to one meter.
But it wasn’t always this accurate when GPS was first developed it was supposed to provide public accuracy of 100 meters, but somewhat accidentally turned out to be five times better. For a system available to everyone, the military thought this to be too accurate so they implemented selective availability which added a random offset to the public signal, but still retained accuracy on the encrypted signal which only the military could use.
So now public institutions had to work with a signal that was significantly less accurate so that led to the development of differential GPS which improves accuracy by using reference points, take a landmark someplace you know the exact coordinates of, stick a GPS receiver on top and you can always compare its actual location with the location the receiver calculates and apply that difference to other receivers nearby. but the artificial offset is not the only thing that affects accuracy GPS satellites broadcast in the location but slight deviations in orbit can often not be avoided and while the atomic clocks are really precise over a life span of multiple decades the clocks go ever so slightly wrong. location inaccuracies and clock drift are the same around the globe and can be easily compensated, but for the signal to get from the satellite to the ground they have to go through the atmosphere. Atmospheric distortions are much harder to deal with because they are highly local, depending on where you’re on the signal has to travel further and the atmosphere itself changes all the time, so generating a single offset isn’t enough, it is why there are a number of these stations all around the globe.
The issue is how to get these corrections to the receiver one way is to simply broadcast them locally the US Coast Guard did just that and by the late 1990s at most ports and maritime whatever is covered but that still left a large part of the continental US without the improved accuracy which brings us back to satellites. to improve navigation in aviation the FAA worked on a system to broadcast these differential information via satellites to make them available all around the u.s. by now there are multiple differential GPS systems available in different parts of the world both terrestrial and satellite based all of these systems ended up making GPS more accurate then it could ever be on its own more accurate even the GPS would be without artificial distortion which made selective availability useless so with an executive order from Bill Clinton it was finally turned off in the year 2000 that is why the European Union launched Galileo to have a system of its own where no one else can flip a switch.