TABLE OF CONTENTS The launch of Sputnik I by the USSR in October 1957 was the beginning of the age of navigational satellites. That event was the culmination of centuries of navigation based on the known position of natural heavenly bodies and ever-improving clock accuracy. Observations of the signals transmitted by Sputnik I established the idea that accurate timing signals coming from artificial satellites of known position could aid navigators substantially. In effect, the artificial satellite replaced the functions of the sun and star tables with the known ephemeris of the satellite. In addition, the satellite's accurate timing signals replaced the ship's chronometer. The satellite-based system could provide continuous, worldwide coverage with few satellites; it could be an all-weather system, and it could provide extraordinary position location accuracy.
The challenge of Sputnik I led to the U.S. satellite system Transit I. Begun in December 1958, its goal was continuous, worldwide, all-weather coverage. Transit was placed in operation January 1964. During the late 1960s, the growing need for accurate navigation among the U.S. strategic and tactical forces, combined with the rapid reduction in the cost of computers and processors (user equipment) established the need for, and potential feasibility of, a highly accurate tri-service navigational satellite system. The Air Force and Navy began independent programs called, respectively, 621B and TIMATION. NAVSTAR/GPS is the program that...
