GPS - Global Positioning Systems - It's a Space Thing!

Yeah, we've all seen the GPS units in cars. In France, the TomTom units are being used on bicycles for tourists to navigate around Paris.

In San Francisco, you can rent a tiny 2-seater go-cart type contraption that has a guided tour of the city that recognizes where you are based on your GPS location--and changes the commentary accordingly.

In the retail business world, the warehousing operations have their pallets and semitrucks and trailers equipped with GPS units so they can track movements of their merchandise and make the most economical decisions for moving the materials to the required destinations.

In agriculture, farmers can use GPS units on their plows, combines, and other farm equipment to locate themselves in large fields, to grade, level, and plow a field such that water runs in the intended directions to maximize crop growth. (They also use GPS navigation techniques to create mazes in corn fields--most popular during October in preparation for Halloween!)

Aircraft have GPS units in addition to the magnetic compasses and other navigational aides that help them know their ground location.

The Global Positioning System (GPS) uses a constellation of between 24 and 32 medium Earth orbit satellites that transmit precise radiowave signals, which allow GPS receivers to determine their current location, the time, and their velocity.

The GPS design was originally based on ground-based radio navigation systems such as LORAN and the Decca Navigator System developed in the early 1940s and used during World War II.

When the Soviet Union launched the first man-made satellite--Sputnik--in 1957, a team of U.S. scientists was monitoring Sputnik's radio transmissions. The scientists discovered that the Doppler effect caused the frequency of the signal being transmitted by Sputnik to be higher as the satellite approached and lower as it continued away from them. And this was the spark of inspiration that gave them the idea for space-based global navigation systems using satellites as transmitting devices--the scientists realized that since they knew their exact location on Earth, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion. Doing this in reverse is what makes the GPS system work.

In 1960, the United States Navy tested the first satellite navigation system--a five-satellite constellation called "Transit". The rudimentary system provided a navigational fix about once per hour.

In 1967, the U.S. Navy developed the Timation satellite that proved the ability to place accurate clocks in space, a technology that GPS relies upon. In the 1970s, the ground-based Omega Navigation System, based on signal phase comparison, became the first worldwide radio navigation system.

In 1972, the US Air Force Central Inertial Guidance Test Facility at Holloman AFB, New Mexico conducted developmental flight tests of two prototype GPS receivers over White Sands Missile Range, using ground-based pseudo-satellites.

In 1978 the first experimental Block-I GPS satellite was launched.

In 1983, after Soviet interceptor aircraft shot down Korean Airlines Flight 007 that strayed into prohibited airspace due to navigational errors, killing all 269 people on board, U.S. President Ronald Reagan announced that the GPS would be made available for civilian uses once it was completed.

By 1985, ten more experimental Block-I satellites had been launched to validate the concept.

On February 14, 1989, the first modern Block-II satellite was launched.

In 1992, the U.S. Air Force 2nd Space Wing, which originally managed the system, was de-activated and replaced by the 50th Space Wing.

By December 1993, the GPS achieved initial operational capability.

By January 17, 1994 a complete constellation of 24 satellites was in orbit.

Full Operational Capability was declared by NAVSTAR in April 1995.

In 1996, recognizing the importance of GPS to civilian users as well as military users, U.S. President Bill Clinton issued a policy directive declaring GPS to be a dual-use system and establishing an Interagency GPS Executive Board to manage it as a national asset.

In 1998, U.S. Vice President Al Gore announced plans to upgrade GPS with two new civilian signals for enhanced user accuracy and reliability, particularly with respect to aviation safety.

On May 2, 2000 "Selective Availability" was discontinued as a result of the 1996 executive order, allowing users to receive a non-degraded signal globally.

In 2004, the United States Government signed an agreement with the European Community establishing cooperation related to GPS and Europe's planned Galileo system.

Squid graphic courtesy of Squidoo Squid Graphics For Your Lenses! by GreekGeek.