30-APR-1921 :- BIRTH OF Roger L. Easton ,the principal inventor and designer of the Global Positioning System (GPS).

Roger Lee Easton, Sr. 
(April 30, 1921 – May 8, 2014) was an American scientist who was the principal inventor and designer of the Global Positioning System (GPS).He was born in Craftsbury, Vermont.

In 1955, Easton co-wrote the Naval Research Laboratory's Project Vanguard proposal for a U.S. satellite program in competition with two other proposals, including a proposal from the U.S. Army prepared by Wernher Von Braun. The Eisenhower Administration selected Project Vanguard. In 1957, Easton invented the Mini track tracking system to determine the Vanguard satellite's orbit. When Sputnik I was launched, Easton extended the system to actively follow unknown orbiting satellites.

In 1959, he designed the Naval Space Surveillance (NAVSPASUR) system. The Naval Space Surveillance System became the first system to detect and track all types of Earth-orbiting objects. It goes through the 33rd parallel, which is basically coast to coast.

Later in his career at NRL, Easton conceived, patented, and led the development of essential enabling technologies for the United States Global Positioning System (GPS). During the 1960s and early 1970s he developed a time-based navigational system with passive ranging, circular orbits, and space-borne high precision clocks placed in satellites. The idea was tested with four experimental satellites: TIMATION I and II (in 1967 and 1969) and Navigation Technology Satellites (NTS) 1 and 2 (in 1974 and 1977). NTS-2 was the first satellite to transmit GPS signals.