Q&A: The invention of GPS by Greg Milner


This article appears in Issue 15 of Umbrella.
Umbrella: Hi Greg. What actually is GPS?
Greg: GPS – Global Positioning System – is a system run by the US Air Force and wholly owned by the United States Department of Defense and the federal government. It’s a constellation of 24 active satellites that are arrayed in a way so that just about every spot on Earth has a direct line of sight with at least four of them at any given time. GPS is also the network of monitoring stations scattered around the world, all owned by either the Air Force or the National Geospatial-Intelligence, a wing of the Pentagon. And everything is overseen by the GPS master control station at Schriever Air Force base in Colorado.
So if we’re on the phone and pull up Google Maps, how does it tell us where we are?
The GPS chip in your phone works like every other GPS receiver. It first tries to find the four closest satellites with the strongest signals and when it does, determines the transmission time of a signal that’s sent from the satellite to the receiver. The signal has information in it that tells it where the satellite was when it left the satellite and the exact time. The GPS receiver figures out how long it took for the signal to reach it. If it does that simultaneously with at least four satellites it can extrapolate that information, translated into a three-dimensional position: latitude, longitude and altitude.
How did GPS start?
GPS came about because there were a few people in the Air Force, and one in particular, Brad Parkinson, who learned about the concept of ‘passive ranging’, which is the conceptual idea behind GPS. He'd been to Vietnam and was appalled by the way the bombing campaign was conducted there – there was no precision to it. Bombs were just dropped from really high distances just to make it safer for the pilots. And the way he put it to me, it was almost like an act of terror, rather than a way of  fighting a real war. What he saw in GPS was basically a way to create a precision weapons delivery system or “to drop five bombs in the same hole”.
Was GPS used in the 1991 Iraq War?
Greg: Yes, but not how most people think it was (that was mostly laser-guided bombs). In the opening hours of the war, it was used to drop cam lights to guide the way for the bombs, so they could be dropped in exactly the right place. It was also used after the war in things like clearing mines.
Were soldiers using it?
Greg: There were military contractors who were building military-grade GPS receivers but they were doing it so slowly that by the time the war happened, they weren't very many. So as the word of GPS spread around, individual soldiers were calling home and trying to get their families to send them the few civilian GPS receivers that had gone on the market. It was also a great advertisement for GPS in the civilian world.
So when did it start being used for civilian purposes?
Almost from the very beginning a sort of hackerish type who was fascinated by GPS was finding a way to use it. And there was a civilian GPS signal along with the military GPS signal from the start: that was always a precondition of its funding from Congress. 
U: Are ‘darker forces’ utilising it?
Greg: Yes: one of the most surprising things I discovered is how international and universal GPS is. There are certain systems that are similar, but the only one that's got plenty of global coverage and a full satellite constellation is Russia's GLONASS system and it's nowhere near as dependable as GPS. The EU’s Galileo system is coming and China's BeiDou, too. But like I say in my book, if an ISIS terrorist is getting a position fix on his phone, he's using technology that comes courtesy of the US Department of Defense. 
What else is GPS being used for today?
‘Precision agriculture’ is really transforming the way the world grows food because if you know exactly where a seed is planted, and you know exactly to the millimetre where to put the water and fertilizer, and exactly where it is when you dig it up so that you only use the right amount of fuel when you go to those fields, that thing adds up. The savings are astronomical. 
What do you think GPS is doing to us as people?
It may be affecting our ability to navigate. Countless scientists and psychologists talk about the cognitive map – basically the ingrained knowledge we have that allows us to figure out where we are in relation to things around us. When you use GPS, especially when navigating a street or city, you don't really have to have any kind of contextual awareness. So there’s a growing amount of studies that are looking at the ways in which GPS may be essentially eroding our cognitive map, and whether that actually has a sort of neurological component. It's too early to tell, but that might be happening, too.
Moving on to the taxi industry, Uber couldn’t survive without GPS, could it?
Uber is absolutely dependent on GPS. I was in a New York City a cab yesterday, a ‘Green’ one (not Yellow), and they’re only allowed to cruise in the outer boroughs. In Manhattan the main part of midtown is off limits to them unless they’re dropping people off. And the guy was telling me that they have it set up so as soon as they go south of 95th Streer, the meter shuts off automatically, making it impossible for them to pick up fares. That can only be done because of GPS.
What is the future for GPS?
One of the most impressive things about GPS is how little it’s changed since the ’70s and usually when we say that about technology, we’re being critical of it. But the architects of GPS were so forward-thinking that they came up with this system that, although it's constantly being updated, the core technology stays the same.
Could it break down and lead to chaos?
The fear isn't of a global GPS shutdown, but a more localised one – it's easy to jam the GPS signal or spoof it to introduce a signal that nearby GPS receivers think is real. And because GPS is used so much for critical infrastructure, especially for timing, a local outage could have wide-ranging consequences. For example, GPS clocks are used to regulate mobile phone transmission, the handover of one call from one tower to the next. And if you were to spoof a GPS signal so that towers in one area are confused and their clocks go wrong because they’re following a spoof GPS signal with a different time signal, then that could affect mobile phone traffic over a large area. People are going to have to figure out ways to make it stronger or look at alternatives if there’s a GPS shutdown. 
Pinpoint by Greg Milner, is published by Granta books, priced £14.99

Q&A: The invention of GPS by Greg Milner Comments

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