Fifty years ago today — April 13, 1960 — the first navigational satellite was launched from Cape Canaveral on a Thor Able-Star booster.
(Transit satellite. Smithsonian Institute image from http://www.nasm.si.edu/exhibitions/gps/before.html.)
Called Transit-1B (the 1A spacecraft had been lost in September 1959 when the launch vehicle’s third stage failed), the small spin-stabilized Navy satellite and its later companions proved the feasibility of using satellite signals for geolocation. Transit paved the way for the Global Positioning System we know today.
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