ABSTRACT
In the early 1970s the Department of Defense (DoD) commissioned a study to define its future positioning needs. That study found nearly 120 different types of positioning systems in place, all limited by their special and localized requirements. The study called for consolidation and NAVSTAR (navigation system with timing and ranging) Global Positioning System (GPS) was proposed. Specifications for the new system were developed to build on the strengths and avoid the weaknesses of its forerunners. Here is a brief look at some of the earlier systems and their technological contributions toward the development of GPS.
