The GPS program is divided into three phases

The first phase was the program validation and preliminary design phase.

        From 1978 to 1979, four test satellites were launched by Gemini rockets from Vandenberg Air Force Base in California, with a long half-axis orbit of 26,560km and an inclination of 64 degrees, and an altitude of 20,000km. This phase mainly developed the ground receiver and established the ground tracking network, and the results were satisfactory.

The second stage is the comprehensive development and testing stage.

        From 1979 to 1984, seven test satellites called BLOCK I were launched successively, and receivers for various purposes were developed. Experiments show that GPS positioning accuracy far exceeds the design standard, using coarse code positioning, its accuracy can reach 14 meters.

The third stage is the practical networking stage.

        On February 4, 1989, the first GPS working satellite was successfully launched, and the satellites in this phase are called BLOCK II and BLOCK IIA. This phase announces that the GPS system has entered the engineering construction state. 1993 the end of the practical GPS network that is (21+3) GPS constellation has been completed, and in the future it will be replaced according to the plan to replace the failing satellites.