America’s Gift to the World

In 1973 the Navy and the Air Force were each building their own way to navigate by satellite. The Pentagon told an Air Force colonel named Brad Parkinson to build one system for every service. He took the best of each: Navy clocks, Air Force signals, orbits high enough to cover the planet. Twenty-two years later it was fully operational, and the whole world could use it.

1. October 1957 · Laurel, Maryland

   Listening to Sputnik

   The Soviet Union launches Sputnik on 4 October. Days later, at the Johns Hopkins Applied Physics Laboratory, physicists William Guier and George Weiffenbach record its radio beeps and measure how the pitch shifts as it passes overhead. From that Doppler shift alone, on a single pass, they work out its orbit. APL’s Frank McClure turns the idea around: if you know where the satellite is, the same shift tells you where you are.

2. 1959–1967 · Transit

   The Navy navigates by satellite

   APL builds the Transit system for the Navy’s Polaris missile submarines. The first prototype flies in September 1959. By the end of 1964 the lab has launched 15 navigation satellites, and Transit enters naval service. In 1967 Vice President Hubert Humphrey opens it to the ships and aircraft of every nation. Transit is slow and gives only latitude and longitude, but it proves that navigation from space works.

3. 1963–1972 · Washington and Los Angeles

   Clocks and codes

   Two teams chase something better. At the Naval Research Laboratory, Roger Easton’s Timation program puts precise clocks in orbit, starting with a satellite launched on 31 May 1967. In Los Angeles, the Aerospace Corporation under Ivan Getting has studied navigation from space since 1963, work the Air Force names System 621B. In tests over White Sands in 1971 and 1972, 621B receivers fix aircraft positions to a hundredth of a mile, using transmitters on the ground and on balloons.

4. Labor Day weekend 1973 · The Pentagon

   The lonely halls

   In April the Pentagon puts the Air Force in charge of one joint program, under Col. Brad Parkinson. In August a review board turns him down: the plan is just 621B in new clothes. Over the holiday weekend Parkinson gathers about a dozen officers and engineers in the quiet Pentagon. The design that emerges takes 621B’s signal, the Navy’s atomic clocks and a higher orbit that circles the Earth twice a day. On 17 December the board approves it.

5. 22 February 1978 · Vandenberg AFB, California

   Navstar 1

   An Atlas F, a retired intercontinental missile, lifts Navstar 1 into orbit, the first GPS satellite. It goes to work on 31 March. The Navy’s test satellites have already flown the first atomic clocks in space, starting in 1974. Rockwell International builds eleven Block I satellites, launched through 1985. Several outlast their three-year design life by more than ten years. Testers try the first receivers in the Arizona desert against ground transmitters standing in for satellites.

   

6. Every orbit · 12,550 miles up

   Einstein’s correction

   GPS runs on time. Each satellite broadcasts the exact time from its atomic clocks, and a receiver turns the delay into distance. Here Einstein matters. Orbital speed slows the satellite clocks by about 7 microseconds a day. Weaker gravity speeds them up by about 45. Left alone, they would run 38 microseconds a day fast, and fixes would drift about six miles a day. So before launch each clock is set to tick at 10.22999999543 MHz instead of 10.23.

7. 16 September 1983 · The White House

   Open to every airliner

   On 1 September a Soviet fighter shoots down Korean Air Lines Flight 007 after it strays over Soviet territory, killing all 269 people aboard. Two weeks later the White House announces President Reagan’s decision: when GPS is ready, the world’s civilian aircraft may use it. In 1991 the United States offers the civil signal to the whole world with no direct charge to users.

   White House statement, 16 September 1983The President has determined that the United States is prepared to make available to civilian aircraft the facilities of its Global Positioning System when it becomes operational in 1988.
8. 1990–1991 · Persian Gulf

   The first GPS war

   Sixteen GPS satellites are working during the Gulf War, and the Pentagon has too few military receivers. It switches off the deliberate blurring of the civil signal and buys 10,000 commercial sets from Trimble and 3,000 from Magellan. Soldiers tape them to dashboards and helicopter panels. Tank columns cross a desert with few roads and few landmarks. Artillery hits its marks, and B-52 bombers and F-16 fighters navigate by satellite.

9. 1 May 2000 · Washington

   Ten times sharper

   The constellation reaches 24 satellites in December 1993, and Air Force Space Command declares GPS fully operational on 17 July 1995. One limit remains. A feature called Selective Availability still blurs the free civil signal to about 100 meters. On President Clinton’s order, the blurring stops at midnight. Overnight, civilian receivers everywhere become up to ten times more accurate.

   President Bill Clinton, 1 May 2000Civilian users of GPS will be able to pinpoint locations up to ten times more accurately than they do now.