50 Fun Facts About GPS

What do the letters GPS stand for?

It is one of several global navigation satellite systems, or GNSS.

Which country's government owns and operates GPS?

It is treated as a national resource but is freely accessible to anyone with a receiver.

Which branch of the US military has owned GPS since 2019?

Mission Delta 31 operates it from Schriever Space Force Base near Colorado Springs.

How many satellites make up a full GPS constellation?

Between 24 and 32 are usually flying, so several are visible from any point with a clear horizon.

What is the minimum number of satellites a receiver needs in view to compute a normal position fix?

Three for the position coordinates and one more to solve for the receiver's clock error.

At roughly what altitude do GPS satellites orbit?

Each completes two orbits per sidereal day, repeating the same ground track daily.

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

Precisely half a sidereal day, 11 hours 58 minutes.

How many orbital planes are the GPS satellites arranged in?

The original plan was three planes of eight; it became six planes tilted about 55 degrees.

In what year was the GPS project started by the US Department of Defense?

About twelve military officers met at the Pentagon over Labor Day weekend to discuss a Defense Navigation Satellite System.

In what year was the first experimental Block I GPS satellite launched?

Ten Block I prototypes flew between 1978 and 1985, and one more was lost in a launch failure.

In which year did GPS achieve initial operational capability with a full 24-satellite constellation?

Full Operational Capability for the military's secure service was declared in April 1995.

What was the name given to the individual GPS satellites?

Two Navy predecessor systems shared the same naming habit; GPS combined their ideas.

Which 1957 event led two Johns Hopkins physicists to realise satellites could be tracked, and users located, by the Doppler effect?

William Guier and George Weiffenbach's work led to the Navy's first satellite navigation system for Polaris submarines.

Which Naval Research Laboratory satellite carried the first atomic clock into orbit in 1974?

Proving that accurate clocks could work in space was essential to the GPS concept.

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

The 747 had strayed into Soviet airspace through navigational error and all 269 aboard died.

What was the name of the policy that deliberately degraded the civilian GPS signal to roughly the length of a football field?

It limited accuracy to about 100 metres and was temporarily switched off during the Gulf War because troops were using civilian units sent from home.

Which US president ordered the deliberate civilian signal degradation switched off, effective 1 May 2000?

Civilian accuracy improved roughly twentyfold overnight.

How accurate was GPS for civilians once the deliberate degradation was discontinued in 2000?

Modern L5-band receivers reach 30 centimetres, and survey gear can hit sub-millimetre over time.

By how much do the clocks on GPS satellites run fast each day, as predicted by relativity and corrected in the design?

Friedwardt Winterberg had proposed testing general relativity with orbiting atomic clocks back in 1955.

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

Iraqi forces also demonstrated its vulnerability by installing radio jammers on likely targets.

Which mathematician's geodetic Earth model was instrumental to GPS and earned her a place in the Air Force Space and Missile Pioneers Hall of Fame in 2018?

She worked at the Dahlgren Naval Proving Ground in Virginia.

Which two men, of The Aerospace Corporation and the Applied Physics Laboratory, are usually credited with inventing GPS and shared the 2003 Draper Prize?

Roger Easton of the Naval Research Laboratory received the National Medal of Technology in 2006.

Which award did four GPS founders, including Bradford Parkinson, receive on 12 February 2019?

Hugo Fruehauf, James Spilker and Richard Schwartz shared it; the citation called engineering the foundation of civilisation.

Where is the GPS master control station?

Command moved there from Onizuka Air Force Station in California in 1988; dedicated ground antennas sit at Kwajalein, Ascension, Diego Garcia and Cape Canaveral.

What is Russia's equivalent of GPS called?

Developed at the same time as GPS, it lacked full global coverage until the mid-2000s.

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

It began operation in 2016 and was fully deployed by 2020; the FCC approved its use in the US in 2018.

Which country's BeiDou system began global services in 2018?

Japan's QZSS is a regional augmentation system for Asia-Oceania.

How accurate can a smartphone's GPS be when helped by services like Wi-Fi positioning?

High-quality standard receivers managed better than 3.5 metres horizontally by 2015.

How much did the GPS programme cost, including launches but not user equipment, according to the estimate cited?

That is about $11 billion in 2025 dollars; only the Cold War nuclear threat was thought to justify it.

How often does the ten-bit GPS week number roll over to zero?

That is about 19.6 years; the second rollover happened on 6 April 2019.

How does GPS time differ from Coordinated Universal Time?

The navigation message broadcasts the offset, which can accommodate up to 255 leap seconds.

Which Navy predecessor system, first tested successfully in 1960, gave submarines a fix about once an hour from five satellites?

Its updates were too slow for fast-moving Air Force aircraft, which is why 621B and the NRL's clock satellites were pursued too.

Above what altitude and speed are GPS receivers classified as munitions under US export rules?

The rule aims to stop receivers being used to guide missiles; some units stop working even when stationary.

When was the first modern Block II GPS satellite launched?

The 24th satellite followed in 1994.

Which of these newer civilian GPS signals offers accuracy of about 30 centimetres?

As of March 2026, 21 satellites broadcast it, with a full 24 expected in 2027.

Which US vice president announced plans in 1998 for two new civilian GPS signals, an effort Congress named GPS III?

The first modernised satellite with the L2C signal launched in 2005.

Which location-based mobile game is named as an example of recreational GPS use, alongside geocaching?

Geodashing, GPS drawing and waymarking are on the same list.

How many satellites are usually visible at any time from any point on Earth with a clear horizon?

That gives plenty of redundancy over the minimum needed for a fix.

What is the estimated cost to the US economy of a day without GPS?

Which is why the Defense Department is required by law to keep the standard service running worldwide.

Which company's proposed ground network in the neighbouring 1525-1559 MHz band was found in 2011 to cause 'significant jamming' of GPS?

The FCC had licensed the spectrum next to the GPS L1 band since 1996.

What did President Clinton's 1996 policy directive declare GPS to be?

It set up an Interagency GPS Executive Board at the suggestion of Defense Secretary William Perry.

Roughly how many years behind schedule was the OCX ground control system when the military accepted Blocks I and II in July 2025?

It was also roughly $4 billion over budget, blamed on monolithic development and feature creep.

Which company unveiled the NAV 1000, the world's first commercial handheld GPS receiver, in 1989?

The units initially sold for around US$2,900 each.

Which 1990 car was the first production model with a built-in satellite navigation system?

Mitsubishi followed a year later with its Multi Communication System on the Debonair.

Which Sony portable GPS unit was the first to feature swappable map database cards?

Aimed at aviators and boaters, it followed the IPS-360, one of the first relatively affordable portable receivers.

In which year did Russia's GLONASS achieve full global coverage?

Like GPS, it operates with 24 active satellites and serves both civilians and the Russian Aerospace Defence Forces.

Europe's Galileo system reached global Early Operational Capability on which date?

The estimated €10 billion project's first experimental satellite had gone up in 2005; the last of its 24 active satellites launched in December 2021.

India's regional NavIC system uses a constellation of how many satellites?

Three sit in geostationary orbit and four in geosynchronous orbit, aiming for accuracy better than 7.6 metres over India.

How many satellites made up Japan's QZSS enhancement to GPS when services began in 2018?

Its first satellite launched in September 2010 and services began on a trial basis in January 2018.

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

Japan's equivalent is MSAS and Russia's is SDCM; all such systems sharpen the accuracy of GNSS signals.