49 Fun Facts About GPS

What do the letters GPS stand for?

Global Positioning System, not 'Satellite': the satellites are only one of three parts, alongside the ground stations that steer them and the receiver in your hand.

Which treasure-hunting hobby was born in May 2000, days after civilian GPS signals suddenly became far more accurate?

Geocaching: on 3 May 2000 Dave Ulmer hid a bucket of trinkets in the woods of Oregon and posted its coordinates online. Within three days, two strangers had tracked it down.

Which branch of the US military operates the GPS satellites?

The Space Force, founded in 2019, took GPS over from the Air Force. US law obliges the Pentagon to keep the civilian signal on worldwide, free of any direct user fee.

What does every GPS satellite broadcast?

Its position and time: a receiver works out where it is from how long each signal took to arrive. Because receivers only listen and never transmit, any number of them can use GPS at once.

A GPS fix needs a fourth satellite to correct an error in the receiver's what?

Clock: the cheap clock in a phone drifts, and light covers about 300 metres in a millionth of a second, so a tiny timing slip would wreck the fix.

GPS satellites fly about 20,000 km up, in which class of orbit?

Medium Earth orbit: at about 20,200 km, the satellites are spread over six orbital planes so that at least four are in view from virtually anywhere on the planet.

How long does one GPS satellite take to orbit the Earth?

About 12 hours: two laps for every turn of the Earth means each satellite retraces the same track over the ground day after day.

GPS satellites also carry sensors that detect what?

Nuclear explosions: every GPS satellite doubles as a lookout for the flash and radiation of a bomb going off anywhere on the globe, helping to police the treaties that ban nuclear tests.

Which company's rocket launched the first GPS III satellite in December 2018?

SpaceX: unusually, the Falcon 9 booster made no attempt to land afterwards. The Air Force wanted every drop of the rocket's performance spent on the satellite, leaving no fuel for the trip home.

GPS stations track which drift of a few centimetres a year?

Tectonic plates: by re-measuring the distance between fixed points, GPS tracks the plates directly. The Atlantic is widening by about 2.5 cm a year, roughly the speed at which fingernails grow.

The GPS III satellites carry nicknames such as Vespucci, Sacagawea and Amelia Earhart, honouring what kind of people?

Explorers: the third satellite was to be Columbus, but before its 2020 launch it was renamed for Matthew Henson, the Black American who reported reaching the North Pole with Robert Peary in 1909.

What was the name given to the individual GPS satellites?

Navstar: the name arrived in 1973, when a Labor Day weekend meeting at the Pentagon folded rival Navy and Air Force satellite projects into a single programme.

Which event showed two Johns Hopkins researchers that Doppler shifts could be used to navigate?

The launch of Sputnik 1: by timing the shift in its beeps, the pair could plot its orbit. Their director then flipped the trick: if you know where the satellite is, you can find out where you are.

In the 1970s the Navy's Timation satellites proved that which devices, vital to GPS, could survive and work in orbit?

Atomic clocks: a test satellite launched in 1974 carried the first into orbit. Clockmakers had to shrink a laboratory instrument and harden it for space without losing the stability that makes it useful.

The shooting down of which airliner in 1983 prompted President Reagan to promise GPS to civilians?

Korean Air Lines Flight 007: a navigation slip let the 747 stray into Soviet airspace, where a fighter shot it down and all 269 aboard died. Reagan wanted no airliner to get lost like that again.

What was the name of the policy that deliberately blurred civilian GPS fixes by about the length of a football field?

Selective Availability: the satellites deliberately fudged their timing so that civilian fixes wandered by up to 100 metres, while military receivers held the key to strip the error out.

Which US president ordered the deliberate degradation of civilian GPS signals switched off?

Bill Clinton: the blurring stopped within hours of his announcement on 1 May 2000. The military had decided it could deny GPS to an enemy region by region instead of degrading it for the whole world.

In 2013 Texas students lured an $80 million yacht off course by attacking its GPS with a trick known as what?

Spoofing: unlike jamming, which merely drowns the real signal out, the fake signals set off no alarm. The ship turned and those aboard could feel it, yet the chart on the bridge still showed a straight line.

GPS fixes would drift by about 10 km a day if the satellites' clocks ignored which branch of physics?

Relativity: speed slows the orbiting clocks, but weaker gravity up there quickens them by more. The net gain is 38 millionths of a second a day, so each clock is set to tick slightly slow before launch.

Which was the first war in which the US military widely used GPS?

The Gulf War of 1990-91: GPS let coalition troops find their way across empty desert, but military receivers were so scarce that the Pentagon had to buy civilian sets to meet demand.

Which mathematician spent four decades at a US Navy base modelling the Earth's true shape, work that underpins GPS?

Gladys West: at Dahlgren in Virginia she programmed an early IBM supercomputer to map the planet's lumps and dips. She retired at 68, suffered a stroke, and went on to finish a PhD anyway.

A global map of GPS-tracked runs from the fitness app Strava was found in 2018 to reveal what?

Secret military bases: soldiers jogging laps with fitness trackers had drawn glowing outlines of remote outposts in Afghanistan and Syria. An Australian student was the first to point it out.

In 2019 four pioneers of GPS shared the Queen Elizabeth Prize, a major international award in which field?

Engineering: the prize rewards innovation of global benefit to humanity, and GPS qualifies handsomely, since billions of people with a smartphone now rely on it to find out where they are.

The GPS master control station sits at Schriever, a military base in which US state?

Colorado: from Schriever, near Colorado Springs, an active-duty squadron and a reserve unit, together nicknamed Team Blackjack, fly the whole constellation day and night.

What is Russia's equivalent of GPS called?

GLONASS: begun by the Soviet Union, it decayed in the 1990s and was rebuilt to a full 24 satellites in 2011, because Moscow did not want to rely on an American system that could in theory be switched off.

What is the European Union's global navigation satellite system called?

Galileo, after the Italian astronomer: unlike GPS it is under civilian control, and the chief reason for building it was independence, so that Europe need not rely on a system another power could switch off.

Which country completed BeiDou, its own global rival to GPS, with a final satellite launch in June 2020?

China: BeiDou is the Chinese name for the Big Dipper, the bright stars that travellers have long used to find north, which makes it a fitting name for a navigation system.

Under open sky, a typical smartphone's GPS fix is accurate to within about what distance?

5 metres: when over a thousand online students in a hundred countries tested their own phones, the average came to 4.9 m.

In March 2025 a receiver built for NASA and Italy's space agency became the first to get a GPS fix where?

On the Moon: about 225,000 miles from home, a receiver on the Blue Ghost lander picked up navigation satellites built to serve Earth. NASA hopes future lunar crews can find their way the same way.

In April 2019, what made some older GPS devices reset their calendars by nearly 20 years?

A week counter hitting its limit: GPS numbers its weeks with only ten binary digits, so after week 1,023 the count returns to zero. It happens every 19.6 years, and the press called this one a mini Y2K.

How does GPS time differ from Coordinated Universal Time?

It is not corrected with leap seconds: GPS time matched world time in 1980 and has ignored every leap second since, so it has run 18 seconds ahead since 2017. Receivers quietly subtract the gap.

Which Navy satellite system, first tested in 1960, let submarines fix their position decades before GPS was ready?

Transit: a navigator had to track a single satellite for about 15 minutes as it crossed the sky to work out one fix. It served the Navy's submarine fleet from 1964 into the 1990s.

Many GPS receivers cut out above 18 km and 1,000 knots, thanks to export rules meant to stop them guiding what?

Missiles: the limits are meant to keep a shop-bought receiver out of a fast, high-flying weapon. Some cut out on height alone, which catches hobbyists whose balloons climb to 30 km.

In 1999 a GPS unit anchored at the top of which peak led National Geographic to add two metres to its height?

Everest: the receiver gave 8,850 metres, two more than the figure in use since the 1950s. In 2020 the two countries that share the peak jointly settled on 8,848.86 m.

The third civilian GPS signal, L5, is broadcast in a protected radio band reserved for the safety of what?

Aviation: L5 is stronger than the original civilian signal, and an aircraft that listens to both can cancel out the delay that the upper atmosphere adds to each one.

Which 2016 mobile game sent players out into real streets and parks, using GPS to find and catch virtual creatures?

Pokemon Go: it was downloaded more than 500 million times in 2016, and within a week of its release Nintendo's market value had risen by $9 billion.

What was a driver doing with the GPS jammer that upset Newark airport?

Hiding from his boss: the jammer blinded the tracker his employer had fitted to the company truck, but in 2012 it also upset a GPS landing system on test at Newark. The FCC proposed a fine of nearly $32,000.

A 2019 study for the US government estimated that a day without GPS would cost the American economy how much?

$1 billion: the same study warned the bill could run half as high again if GPS failed for weeks in the spring planting season, because so many American farmers now steer by it.

Which navigation app, bought by Google in 2013, spots traffic jams from the GPS speeds of its own users?

Waze: every phone running the app reports its speed and position, so the drivers themselves become the traffic sensors. Apple and Facebook were both reported to be circling the Israeli start-up before Google won it.

What did a 1996 presidential directive declare GPS to be?

A dual-use system managed as a national asset: a board led jointly by the Pentagon and the Transportation Department took charge. The directive also promised to stop blurring the civilian signal within a decade.

How do flight-tracking sites such as Flightradar24 know where most airliners are?

Planes broadcast their own position: an airliner continually announces where its GPS receiver says it is. Volunteers around the world pick the signals up on home receivers and feed them to the site.

Which company launched the NAV 1000, the first handheld GPS receiver sold to the public?

Magellan: the young firm built its battery-powered NAV 1000 for hikers, boaters and other weekend adventurers. An early unit is now kept in the Smithsonian's collection.

GPS is American, but the first production car with built-in GPS navigation went on sale in 1990 in which country?

Japan: Mazda fitted it to its Eunos Cosmo coupé. Honda had sold Japanese drivers a navigator as early as 1981, which tracked the car with a gyroscope and showed its path under transparent map sheets.

Farmers who let GPS steer their tractors save seed, fuel and fertiliser mainly by avoiding what?

Overlapping passes: steered by satellite, a tractor neither covers a strip twice nor skips one. It can also hold its line through dust, fog and darkness, when a human driver could not see the last row.

Russia lost three navigation satellites in 2013 because rocket sensors were fitted how?

Upside down: investigators found signs that several sensors had been forced into place the wrong way round. Fed false readings about its own motion, the rocket swerved wildly and fell back to Earth in flames.

A 1996 US rule that helped put GPS into ordinary phones was meant to help whom?

Emergency dispatchers: a 911 caller on a mobile often cannot say where they are. Networks had to report the caller's latitude and longitude, and a GPS chip in the handset proved a neat way to get it.

India named its satellite navigation system NavIC, which sounds like the Hindi word for what?

Sailor: the name is also short for Navigation with Indian Constellation. It suits the job, since the system can send storm and disaster warnings to fishermen out at sea.

Which GPS problem is beaten by always keeping one satellite almost directly above Tokyo?

Tall buildings: in a street of skyscrapers only a satellite high overhead stays in view. The Quasi-Zenith satellites, whose name means nearly overhead, trace a lopsided figure of eight that lingers in the north.

Which satellite-based augmentation system serves India, as WAAS does the US?

GAGAN: ground stations across India measure the errors in GPS signals and satellites parked over the region broadcast corrections, sharpening a fix enough to guide airliners in to land.