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The VANGUARD satellite launching vehicle is a three-stage rocket of which the first two stages are guided and the third stage is maintained in a fixed orientation while it is firing. The first stage, an improved Viking, serves primarily to raise the remaining stages to altitude. The second stage, another liquid-propellant rocket, contains the guidance for the three-stage vehicle and, in addition, supplies some of the propulsive energy. The third stage, a solid-propellant rocket, is ejected from the second stage at orbital altitude and provides about half of the required orbital velocity. The VANGUARD launching vehicle system was chosen from a number of possible two- and three-stage vehicle combinations. It represents the smallest satellite launching vehicle consistent with the present state of rocket development.