Transit had its inception just days after the launch of Sputnik on October 4, 1957. Two scientists of The Johns Hopkins University Applied Physics Laboratory (APL) -- George Weiffenbach and William Guier -- were able to determine Sputnik's orbit by analyzing the Doppler shift of its radio signals during a single pass. Frank McClure, then chairman of APL's Research Center, went a step further by suggesting that if the satellite's position were known and predictable, the Doppler shift could be used to locate a receiver on Earth; in other words, one could navigate by satellite.
With early funding from the Advanced Research Projects Agency (ARPA), the development of the system began at APL in 1958 under the leadership of Richard Kershner. The Navy assumed responsibility for the system in 1960, and by the end of 1964 APL had designed, built, and launched 15 navigation satellites and eight related research satellites; established a worldwide network of tracking stations; determined the Earth's gravity field with enough accuracy to permit a satellite's orbit to be predicted for more than 12 hours; developed the system software; measured the satellite's environment; and overseen the development of operational ground stations and shipboard equipment.
The first prototype satellite was launched in September 1959, and the system entered Naval service in 1964.The system provided passive, accurate, reliable, all-weather global navigation for Navy submarines and surface ships.
In the summer of 1967,Vice President Hubert Humphrey announced that the system was available to commercial ships and aircraft of all nations, and in October he presented Dr. Kershner with a Distinguished Public Service Award. The last Transit satellite launch was in August 1988.
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The Transit constellation consisted of two types of spacecraft designated as Oscar (pictured left) and Nova (right). The final constellation consisted of six satellites (all Oscars) in a polar orbit with a nominal 600 nautical mile altitude, three ground control stations, and receivers (i.e., the system's users). Of the six satellites, three Oscars provided navigation service while three other Oscars were "stored-in-orbit" spares.
Eventually, the number of commercial, cruise, and sporting vessels using the system worldwide was in the tens of thousands -- far outnumbering the military users. Transit proved essential for the recovery at sea of early manned space vehicles, and it became the standard for precision land surveying and the locations of platforms at sea. Accurate, always available navigation improved the safety and efficiency of shipping operations around the globe.
The Transit system spawned a number of space "firsts," including the two-frequency method for correcting ionospheric error, solar attitude detectors, dual-launch payloads, satellite electronic memory an uplink authentication system, and gravity-gradient stabilization. Additional improvements during the life of the system included development of satellite compensation for drag and radiation pressure, the use of pulsed plasma micro-thrusters, and hardening of the spacecraft against an enhanced radiation environment.
Development of Transit demanded great strides in many areas of space science and technology, including electronic devices, circuit and packaging design, advances in mechanical design, new materials, control of satellite operations, software development, and the use of modeling and simulation.
Today, the legacy of Transit may be seen
in the application of many of its innovations and discoveries
to scientific and engineering endeavors and to products that benefit
mankind. These include the following:
In October 1996, APL received a Defense Certificate of Recognition for Acquisition Innovation award for its achievements in the Transit Navy Navigation Satellite System. Presented by the Office of the Assistant Secretary of the Navy for Research, Development, and Acquisition, the award is one of only two Defense Certificates of Recognition and 1,300 acquisition excellence awards given out in a community of more than 41,000 eligible organizations. The citation noted that as the system evolved over 30 years of operation, hardware upgrades to the tracking system were required only three times."
At the end of 1996 Transit, the Navy Navigation Satellite System, was retired after more than 32 years of continuous, successful service to the U.S. Navy.