Why GPS Is Free

It's Tuesday, September fifteenth. GPS — the Global Positioning System — is the most expensive public utility ever built. It cost somewhere north of twelve billion dollars to put the satellites up there, and it costs roughly two million dollars a day to run. You have certainly paid for the devices that use it. The first handheld GPS receiver, the Magellan Nav 1000, cost three thousand dollars in 1989 — and all it did was show you your latitude and longitude. For years, car companies charged two or three thousand dollars for a built-in navigation system, and Garmin and TomTom sold millions of dashboard units at hundreds of dollars each. People paid real money to use GPS.

But nobody has ever paid for the signal itself. There is no GPS tax. No subscription fee to access the satellite broadcast. The United States government spent somewhere north of twelve billion dollars to put those satellites in space, spends about two million dollars a day to maintain the constellation, and gives the signal to the entire planet for free. That is genuinely strange. Most public infrastructure this useful and this expensive eventually finds a way to bill you. GPS never has. The reason involves a passenger jet shot down over Soviet airspace, four atomic clocks screaming through space at fourteen thousand kilometers an hour, and a president who decided, on the first day of May in the year 2000, to turn off the switch that had been lying to civilian receivers for a decade.

The story started, like a surprising number of space stories, with the Soviets freaking out the Americans. October 1957. Sputnik went up — a polished metal sphere about the size of a beach ball, beeping a radio signal back to Earth. American scientists at the Applied Physics Laboratory at Johns Hopkins started listening to that beep, and they noticed something. When the satellite was moving toward their receiver, the beep sounded slightly higher in pitch. When it was moving away, the pitch dropped. This was the Doppler effect — the same thing that makes a siren sound higher as an ambulance approaches and lower as it passes you. The shift tells you how fast the source is moving relative to you.

Two physicists named William Guier and George Weiffenbach realized that if you tracked this frequency shift very carefully over time, you could work out the satellite's entire orbit. Their boss, Frank McClure, inverted the logic. If you can figure out a satellite's orbit from a known position on the ground, you can figure out a position on the ground from a satellite with a known orbit. The seed idea of GPS — using satellites as navigation beacons — fell out of a beeping Soviet beach ball and two guys with a radio receiver.

The Navy built the first version. It was called Transit, and it went operational in 1964. Submarines used it. Wait for a satellite to pass overhead — which might take an hour or two — and you could get a position fix good to a couple hundred meters. Useful, but not exactly turn-by-turn.

On Labor Day weekend 1973, an Air Force colonel named Bradford Parkinson sat in a Pentagon conference room with a small team of engineers. They'd been told to take the best pieces of three competing satellite navigation programs — Transit, Timation, and something called Project 621-B — and fuse them into one system. The Air Force had already studied twelve different approaches to satellite navigation. Most of them were simpler: put satellites in low orbits like Transit, which meant you didn't need atomic clocks because the Doppler shift alone could give you position. Or build a system where the receiver transmits a signal back to the satellite, so the satellite does the position calculation for you. Parkinson's team rejected all of that. They picked the hardest one on the list: a completely passive system, twenty-four satellites in medium Earth orbit, each carrying its own atomic clock.

Here's why that was harder. Passive means the satellites broadcast and receivers on the ground just listen, silently — they don't transmit anything back. That's important for submarines and soldiers who don't want to broadcast their location by asking the satellite "where am I?" But it also means the receiver has to do all the math itself. To fix its position in three dimensions, a receiver needs simultaneous signals from at least four satellites — three for latitude, longitude, and altitude, plus a fourth to correct for the fact that the receiver's own clock is just a cheap quartz oscillator, not an atomic clock. That means you need at least twenty-four satellites total so that at any moment, from any point on Earth, at least four are above the horizon. And those satellites have to carry clocks precise enough that an error of a single billionth of a second would translate to an error of about one foot in position.

A billionth of a second. That is the precision window.

The clocks they put on these satellites are atomic clocks. An atomic clock doesn't tick like a wristwatch — it counts the vibrations of atoms. A cesium atom, when you hit it with exactly the right frequency of microwave energy, resonates nine billion, one hundred ninety-two million, six hundred thirty-one thousand, seven hundred seventy times per second. That oscillation is so steady, so fundamental to the physics of the atom itself, that cesium clocks drift by roughly one second every hundred million years. These are the timepieces they strap to satellites and shoot into orbit at twelve thousand five hundred fifty miles up, moving at about fourteen thousand kilometers per hour.

But there's a problem. Einstein's relativity.

General relativity says that time passes faster the farther you are from a massive object — meaning the satellite clocks, sitting in weaker gravity than clocks on Earth's surface, run faster by about forty-five microseconds per day. Special relativity says that time passes slower the faster you move — meaning the satellite clocks, screaming through orbit, run slower by about seven microseconds per day. The two effects don't cancel. They leave a net gain of thirty-eight microseconds per day. Thirty-eight microseconds doesn't sound like much, but in GPS terms, multiplied by the speed of light, it's about eleven kilometers of position error per day. Without relativity corrections built into the system, GPS would be useless within minutes.

The engineers knew this. They built a frequency synthesizer into the first cesium-carrying satellite, NTS-2, launched in June 1977, with a switch they could flip after launch if Einstein turned out to be right. They flipped it. He was. The clocks slowed down and the system worked.

September first, 1983. Korean Air Lines Flight 007 took off from Anchorage, Alaska, headed for Seoul. It was a Boeing 747 with two hundred sixty-nine people on board. The crew programmed the autopilot and settled in for a long flight over the Pacific. But something went wrong. The autopilot was not tracking the waypoints they had entered into the inertial navigation system. The plane drifted north. It drifted more than two hundred miles north, over the Kamchatka Peninsula, into Soviet airspace.

Soviet radar picked it up. A US Air Force RC-135 reconnaissance plane had been operating in the same area earlier that night, monitoring a Soviet missile test. The Soviet military mistook the passenger jet for the spy plane. Fighter jets scrambled. A Soviet pilot named Gennadi Osipovich fired two air-to-air missiles. The 747 stayed airborne for another twelve minutes, its pilots fighting for control, before it crashed into the Sea of Japan. No one survived.

The world was horrified. Ronald Reagan called it a "massacre," an "act of barbarism." But he also did something specific and forward-looking. He announced that GPS, until then a purely military system, would be made available to civilian aircraft around the world — for free. The argument was simple. If KAL 007 had had access to GPS, its crew would have known exactly where they were. They would have known they were two hundred miles off course. The tragedy was, in a very direct way, a navigation failure. Reagan framed the free availability of GPS as the open, democratic alternative to Soviet secrecy.

The gesture had a geopolitical logic. But it also set a precedent that would echo for decades. The United States built a trillion-dollar technological infrastructure, funded entirely by the Defense Department budget, and then gave it to the world. For free. No country has ever done anything quite like it.

The first civilian portable GPS receiver hit the market in 1989. It was called the Magellan Nav 1000. It cost three thousand dollars, weighed a pound and a half, ran for a couple hours on a set of AA batteries, and looked like an oversized walkie-talkie from a sci-fi movie. It could tell you your latitude and longitude. That was it. No maps. No turn-by-turn. Just numbers on a screen. People bought it anyway.

There's a catch. For the first decade and a half of civilian GPS, the signal was deliberately degraded. The Pentagon called it Selective Availability. The satellites would introduce random timing errors into the civilian signal — little lies, essentially — so that your position reading could be off by up to a hundred meters. That's the length of a football field. The military signal was ten times more accurate, and that was the point. In a conflict, you wanted your guided bombs to have better GPS than the other guy's.

Throughout the 1990s, civilians worked around it. They built systems called differential GPS, which used a fixed ground station with a known position to calculate the error in the satellite signal and broadcast a correction. It worked, but it was expensive, clunky, and fundamentally absurd. The government was spending millions to put a perfect signal in the sky, then spending more money to degrade it, and private companies were spending more money to correct the degradation. The whole thing was a loop of cost and friction built around a lie.

On May first, 2000, President Bill Clinton issued a statement. Selective Availability would be turned off at midnight tonight. The announcement was a single page, less than four hundred words. The reasoning was partly economic — civilian GPS was by then a multi-billion-dollar industry serving fishing fleets, surveyors, trucking companies, emergency responders — and partly technological. The military had figured out how to jam GPS locally in a conflict zone rather than degrading it globally. They no longer needed to lie to everyone just to deny it to a specific region.

At midnight, Selective Availability went dark. Overnight, civilian GPS accuracy jumped from a hundred meters to about twenty meters. In practical terms, your phone went from knowing roughly which block you're on to knowing which side of the street you're standing on. The civilian GPS industry exploded. Within three years, the market for GPS devices and services more than doubled.

The next day — May third, 2000 — a computer consultant in Oregon named Dave Ulmer hid a collection of objects in the woods, recorded the GPS coordinates, and posted them online. He called it the "Great American GPS Stash Hunt." Three days later, someone found it. That was the first geocache. Within twenty years, more than three million people around the world would go on to hide or search for geocaches. All of it riding on atomic clocks and a presidential decision made on a Monday morning.

GPS now supports an estimated one billion dollars a day in economic activity in the United States alone. It synchronizes power grids, routes ambulances, guides tractors through fields within two inches of accuracy, times financial transactions, and lands planes in zero-visibility fog. The thirty-one satellites currently in the constellation, each the size of a large SUV, will each need to be replaced roughly every fifteen years — a rolling cost, absorbed entirely by the US Air Force budget. No one has ever been charged for it. No one ever will be.

Here is what is strange about GPS, as a piece of infrastructure. It is invisible, it is essential, and it is owned entirely by the US military — yet it is trusted universally. Banks in Zurich, fishing boats off the coast of Japan, Uber drivers in Mumbai, hikers in Patagonia all navigate by a signal controlled by the United States Space Force. The system works because it has to work. If GPS went dark tomorrow, the economic damage would be in the billions per hour. The military knows this. Everyone knows this. And so the clocks keep ticking at twelve thousand miles up, correcting for relativity thirty-eight microseconds at a time, broadcasting a signal anyone can pick up with a chip that costs less than a dollar to manufacture.

Stay informed, stay curious, and we'll see you tomorrow.