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GPS satellite navigation
first satellite 1978; fully working 1995· Invention or discovery· Transport & space
Well documentedSolid records, physical evidence or scientific consensus.
A US military network of satellites that lets a receiver anywhere on Earth find its position and the exact time.
See it on the Technology & Medicine map →How it works
Approved by the Pentagon in 1973, with Air Force officer Bradford Parkinson leading it, the system built on the Navy's Transit and Timation satellites and on Air Force studies. The first satellite launched in 1978; the full 24-satellite system worked by 1995. Each satellite broadcasts its position and the time from atomic clocks. A receiver measures how long signals from four satellites take to arrive and calculates its location. The clocks must be corrected for Einstein's relativity, about 38 microseconds a day.
Why it mattered
Free, precise location and timing now guide ships, planes, farm tractors, surveyors, phone maps and deliveries, and synchronize power grids, banks and phone networks.
Think of it like
Like fixing a property corner by measuring its distance from three surveyed monuments; the fourth satellite corrects the receiver's cheap clock.
How we know
Pentagon and Air Force records, launch logs, and a 2019 study for the US government estimating about $1.4 trillion in private-sector economic benefits since the 1980s.
Still unknown or debated
After a Soviet fighter shot down Korean Air Lines Flight 007 in 1983, Reagan promised civilian use; historians debate whether that changed plans or publicized existing ones.
Connections (3)
▸Magnetic compass was largely superseded by GPS satellite navigationMostly agreed
The connection
For about 900 years, sailors found direction with a magnetised needle and estimated position from speed and time. GPS, fully working from 1995, gives position itself, to within metres, anywhere on Earth. Ships and aircraft still carry magnetic compasses as backups, because GPS signals can fail or be jammed.
When and how
Compass: Song China, described by Shen Kuo in 1088, reaching Europe about 1190. GPS: US Department of Defense, first satellite 1978, full service 1995.
How sure are we?
Navigation practice shows the shift: GPS receivers became standard on ships and aircraft in the 1990s, while international maritime rules still require a magnetic compass on board.
Debates and open questions
Heavy reliance on GPS worries planners; jamming in recent conflicts has revived interest in compasses, star sightings and land-based backup systems such as eLoran.
▸Sputnik 1 led, via satellite tracking, to GPS satellite navigationWell documented
The connection
Days after Sputnik's launch, physicists William Guier and George Weiffenbach noticed its radio pitch shifted as it passed overhead, the Doppler effect, and could calculate its whole orbit from that. Their colleague Frank McClure reversed the idea: if you know a satellite's orbit, you can find your own position. That became the Navy's Transit system, then inspired GPS.
When and how
Johns Hopkins Applied Physics Laboratory in Maryland, October 1957 to 1958; Transit guided Navy submarines from 1964, and GPS was approved in 1973.
How we know
The laboratory's histories and Guier and Weiffenbach's own published account document the chain; Transit was the first working satellite navigation system.
Debates and open questions
GPS also drew on the Navy's Timation clock satellites and the Air Force's Project 621B; how to divide credit among them is still argued.
▸GPS satellite navigation was built into nearly every SmartphoneWell documented
The connection
GPS receivers listen to timing signals from several of about 30 satellites and work out position from tiny delays. Once bulky and military, receivers shrank to a fraction of a chip. Phones gained them partly because US rules required locating 911 callers; the 2008 iPhone 3G added GPS, enabling turn-by-turn maps, ride-hailing and delivery apps.
When and how
US Air Force GPS, fully working 1995; deliberate degrading of civilian signals ended May 2000; first GPS phones 1999; iPhone 3G, July 2008.
How we know
FCC 911-location rules, phone specifications and app histories document the link; Google Maps navigation and Uber, both from 2009, relied on phone GPS.
Debates and open questions
Heavy reliance on GPS worries security experts, since signals can be jammed or faked, as seen in recent conflicts.