As the United States marks its 250th anniversary, 草莓传媒 presents 鈥�250 Years of America,鈥澛燼 multipart series examining the innovations, breakthroughs and pivotal moments that have shaped the nation since 1776.
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Three scientists and a president are responsible for the global positioning satellite boom that transformed transportation, commerce and daily life. While research into satellite navigation dates back nearly 70 years, it was not until the widespread availability of GPS technology that its full impact was realized.
GPS has transformed transportation and made it possible for us to reach destinations more safely and efficiently, allowed airlines to fly with greater precision and enabled consumers to track packages from warehouse shelves to their front doors.
The origins of GPS can be traced to the Cold War. After the Soviet Union launched Sputnik in 1957, American scientists discovered they could track satellites by measuring changes in their radio signals. Researchers soon realized the opposite was also true: if the position of a satellite was known, a receiver on Earth could determine its own location.
In the early 1970s, scientists Roger Easton and Ivan Getting developed the satellite tracking system and Col. Bradford Parkinson led the effort to turn the concept into the Navstar Global Positioning System used today.
The first GPS satellite was launched in 1978, and the system was initially designed to help military aircraft, ships and troops navigate anywhere in the world. A major turning point came in September 1983 after Korean Air Lines Flight 007 was shot down by the Soviet Union after straying into restricted airspace.
鈥淭he 747 is equipped with the most modern computerized navigation facilities, but a computer must respond to input provided by human hands. No one will ever know whether a mistake was made in giving the computer the course or whether there was a malfunction. Whichever, the 747 was flying a course further to the west than it was supposed to fly 鈥� a course which took it into Soviet airspace,鈥� then-President Ronald Reagan said in a nationwide speech from the Oval Office the day after the shootdown took place.
In response, Reagan announced that GPS technology would eventually be made available for civilian use to improve navigation safety worldwide.
That promise became reality in May 2000 when then-President Bill Clinton ordered the end of 鈥淪elective Availability,鈥� a program that intentionally degraded GPS accuracy for civilian users.
鈥淭he decision to discontinue Selective Availability is the latest measure in an ongoing effort to make GPS more responsive to civil and commercial users worldwide,鈥� Clinton said. 鈥淭his increase in accuracy will allow new GPS applications to emerge and continue to enhance the lives of people around the world.鈥�
Clinton鈥檚 prediction proved remarkably accurate. GPS technology is now embedded in nearly every aspect of modern life. Farmers use it to guide tractors with extraordinary precision. Trucking companies track freight in real time. Airlines rely on satellite-based navigation systems. Emergency responders use GPS to locate callers in distress. Ride-sharing services, food delivery apps and smartphone maps depend on it every day.
GPS satellites operate in medium-Earth orbit, about 12,550 miles above the planet. Each satellite circles the Earth approximately every 12 hours, repeating its ground track each day.
Your smartphone or GPS receiver receives signals from multiple satellites. Because those signals travel at the speed of light, the device can calculate its distance from each satellite. Using a process known as trilateration, the receiver determines its position with remarkable accuracy.
There are typically about 31 active GPS satellites in orbit, operated by the U.S. Space Force. At least four satellites are needed to determine an accurate position. Because the satellites orbit so high above Earth, a smartphone can often see between six and 12 satellites at any given time.
What began as a Cold War military research project has become one of the most important technological innovations of the last half-century, quietly guiding billions of people and trillions of dollars in commerce around the globe every day.
And in the future, GPS technology will play a key role in the development of autonomous vehicles, the delivery of packages by drones and other technologies that are on the drawing board now or have not even been thought of yet.
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