The world’s first space-based navigation system was devel oped by the Navy using the initial concept, design, and technical management supplied by Johns Hopkins University’s Applied Physics Laboratory.
The system was called Transit or, more formally, the Navy Navigation Satellite System, and it was the seed of the navigational revolution that blossomed with Global Positioning System. Its mature architecture consisted of three operating and three spare satellites in a 600-nautical-mile polar orbit, three ground control stations, and receivers on naval vessels—beginning in 1967, on merchant vessels as well. A user needed signals from only one Transit satellite to derive a positioning fix, although signals from any given satellite were available for only limited times of the day for a user on the surface. The system did not work as quickly or quite as accurately as GPS, and it was useful in only two dimensions—primarily on the surface of the ocean. Nevertheless, it met the needs of the Navy’s Polaris-carrying submarines, which needed periodic accurate fixes to update their inertial navigation systems.
Perhaps the most fascinating part of Transit’s history is the cause of its conception. Soon after the Soviet Union launched Sputnik 1 Oct. 4, 1957, a small group of scientists at APL was listening to variations caused by the Doppler effect in the satellite’s 20 MHz signal, deducing its closest approach as well as other information about its orbit.
The group was elated when the Soviets launched Sputnik 2 Nov. 3, 1957, thereby allowing them to continue their tracking experiments. One of the scientists, Dr. Frank McClure, reasoned that the Doppler effect could also be used inversely to deduce the position of the receiver if the satellite’s precise orbit were already known. McClure refined the concept and presented it to APL’s director, R.E. Gibson, March 18, 1958.
Soon afterward, McClure and Gibson presented a 50-page proposal for developing the system to the Navy Bureau of Ordnance. The Navy was immediately receptive to the idea, and it enthusiastically sponsored APL’s further work on the concept. Thus the Soviet Union’s first success in space contributed directly to a creative explosion in America’s own space technology.
The newly created Advanced Research Projects Agency took over management of Transit in 1958 and formally initiated the development program Sept. 4, 1958. ARPA assigned the program to the Navy in September 1959. The Air Force Ballistic Missile Division (SMC’s predecessor) provided the launch vehicle and launch.
The first attempted launch—unsuccessful—took place Sept. 17, 1959, from Cape Canaveral Air Station, Fla., using a Thor booster with an Able upper stage.
The second launch attempt took place April 13, 1960, from Cape Canaveral using a Thor booster with an Ablestar upper stage. It successfully placed the world’s first working navigation satellite—Transit 1B—into orbit, and the Ablestar carried out the first engine restart in space to refine the orbit. Transit achieved initial operational capability in 1964 and full capability in October 1968.
Its navigational broadcasts were switched off deliberately on Dec. 31, 1996. The Joint Chiefs of Staff had decided to rely on GPS alone for navigation and positioning.
The Applied Physics Laboratory maintains an excellent web site with historical documents about transit at http://sd-www.jhuapl.edu/Transit/. Most of the information in this article was taken from documents accessible from that site, including some fascinating first-person accounts of Transit’s conception during the broadcasts from Sputnik 1.