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SATELLITE RADIO NAVIGATION
GNSS primordially, is a civillian spin-off of the US defence mission to provide accurate location information for military purpose. The work on NAVSTAR system, which is now more popular as GPS was engineered by Rockwell International. Over 30 satellites were launched in 3 blocks, which became fully operational in 1995. It began with the use of radio navigation in October 1940, when the National Defense Research Council in Washington suggested a system which combines radio signals with time interval measurements. Based on this MIT’s Radiation Laboratory developed LORAN system [Long Range Navigation]. LORAN was developed based on the British GEE radio navigation system. LORAN had far better range of 1200 miles as compared to 400 miles by GEE RNS. LORAN which has the coverage area based on the frequency was used widely in World War-II for navigation by defense forces. Using LORAN the the allied defense forces conducted operations at night and in poor weather conditions. Post World War-II this was put into civilian use for the navigators.

In 1957, the launch of Sputnik-I by USSR, initiated the thought process for the satellite based navigation system. Two scientists in the Applied Physics Laboratory at Johns Hopkins University, Bill Guier and George Weiffenbach observed the Dopler shift in the radio signals received from Sputnik-I, which led to the suggestion that the orbital parameters of Sputnik-I could be measured and based on this the ground position of an object could be determined. In simple terms the strength of the radio signals increased as Sputnik approached and decreased as it left them, was the basis of this concept of satellite based radio navigation.

The usage of satellite navigation and positioning was solely military during that time with specific objective being the control of long range missile. Transit IB became the first navigation satellite launched by US Navy in 1960 followed by SECOR in 1964 by US army. Going by the existing documents on web, it was in 1967 that USSR sent it’s first navigation satellite called Tsyklon.

GPS
In 1970, the US Department of Transportation published the first National Plan for Navigation. It is unclear when the Department of Transportation involved itself with Satellite Navigation. Prior to this it was US Army and Navy which were pursuing satellite navigation programs first through TRANSIT and later through SECOR. Although the involvement of Department of Transportation is one of the most far sighted act, as primarily the transportation department works in civil domain, but in the present scenario and in days to come it would be the largest user or coordinator of user segment.

In 1973, US Navy and Air Force came together to develop the Defense Navigation Satellite System (DNSS), which was later renamed as NAVSTAR. Later in 1974, Rockwell was awarded the contract to develop the NAVSTAR satellite and US DoD declared this tri-service program based on GPS concept to be coordinated by US Air Force.

From 1978 to1994, US completed the constellation of 30 NAVSTAR satellites. In 1993 GPS achieved its Initial Operational Capability and reached it’s Full Operational Capability in 1994. In March 1996 US Govt. released the US GPS Policy

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