The Soviet launch of the Sputnik satellite put fear into the hearts of American military planners. Yet ironically, it marked the beginning of a timeline that led to the Global Positioning System or GPS as we know it today.
In 1957 Scientists working at the Massachusetts Institute of Technology observed that the frequency of the radio signals transmitted by Sputnik increased as the tiny Soviet satellite got closer and decreased as it got farther away.
This was nothing other than the same Doppler Effect that makes an ambulance siren or a street car bell drop in pitch as it moves away from you.
This same effect is used by astronomers to measure the speed of entire galaxies that are rushing away from the Earth.
Since it was possible for any single receiver on the ground to detect and calculate the rate of change of frequencies from a satellite passing overhead, all it took was for the receiver to be able to communicate with two satellites a the same time to be able toe ‘triangulate’ its location on the ground.
Add a third or even a fourth satellite and the calculation would be all that more precise. This was wonderful for the military since it meant that a guided missile like a cruise missile could be sent through an open window from thousands of miles away.
Today the GPS receiver that is built into your smart phone or the standalone GPS device sitting on the dashboard of your car can determine its location by receiving radio signals from two or more satellites (which must be in line-of-sight from the receiver) and calculating the time it takes for the signals to reach the receiver.
Since it is known exactly how far apart each satellite is from the others, it’s a simple matter to then triangulate your precise location. Modern GPS can even determine how fast you are going in miles or kilometers per hour, and it does this from a vantage point 13,000 miles above the Earth!
Today a network of 31 satellites revolve around the earth twice each day, each parked at a stationary point about the planet, allowing GPS to be used reliably by everyone for a wide variety of uses and purposes.
GPS sure has come a long way from the days of Sputnik. Here’s the timeline, and an update.
The first navigation system that relied on satellites was built by the Navy and called TRANSIT. Designed to track sub marines, the system began with six satellites and soon expanded to ten.
The Aerospace Corporation performed a study for the U.S. military under which a network of satellites would continuously send signals to ground receivers which could then determine their exact location according to an exact set of coordinates.
Atomic clocks added a measured of greatly increased accuracy with the new Timation satellite replacing the Transit satellite.
The Air Force debuts NAVSTART featuring a 24-satellite network for the military.
After the shoot down of a Korean passenger jet, the Reagan Administration made GPS available; for civilian uses so that aircraft could avoid inadvertently wandering off course and into hostile territories.
Shortly after the Russians shot down Korean Air flight 007 after it wandered off course into Soviet airspace over the Kamchatka Peninsula, president Reagan offered to let all civilian commercial aircraft use the GPS system (once it was completed) to improve navigation and air safety.
The government contracts with private companies to develop “airborne, shipboard and man-pack (portable)” GPS receivers.
The Air Force finally places the first modern GPS satellite into orbit, launched from a Delta II rocket .
The first hand held GPS navigation device, the Magellan NAV 1000, comes to market in the U.S.
The U.S. military downgrades the accuracy of civilian GPS in order to thwart adversaries who might use it to advantage.
The 24th NAVSTAR satellite is launched, completing the modern array of geostationary satellites.
The CLinton administration informs the airline industry that GPS will continue to be offered free for use “for the foreseeable future.”
The first major revision of the GPS system is complete with 27 GPS satellites in orbit and orbiting the Earth twice daily. Four satellites are now ‘visible’ to a ground receiver at any location on earth at any time of the day or night.
The first GPS phone that is commercially available is the Benefon Esc!, manufactured by Benefon.
The deliberate degradation of GPS is ended with the system instantly becoming more accurate by a factor of ten times. This launches the explosion of vehicular GPS devices and services for both businesses and consumers.
As GPS receiver technology advances and costs drop significantly, increasing numbers of companies like Garvin begin offering a wide array of devised or consumers.
New “assisted’ GPS technology allows cell phones to use both Cell tower triangulation and satellite triangulation at the same time, allowing the end user to pinpoint their location on the Earth’s surface within just a few feet.
The U.S. Air Force currently manages an orbital fleet of 31 GPS satellites, plus three that remain on hold and can be activated as needed.