A ballistic missile trajectory consists of at least three sectors:

• 1. Powered flight from launch until engine cut-off, the point we shall refer to as the burnout point.

• 2. Free flight, which covers most of the trajectory.

• 3. Re-entry, which begins at some point where atmospheric drag forces become a significant factor in determining the subsequent motion of the missile, this sector lasting until impact with the surface of the earth which we shall refer to generally as the ground.

During the free flight sector, the trajectory is part of a conic section—invariably a sector of an elliptic orbit which intercepts the ground—the subject of this article. Figure 1 illustrates some of the important parameters in the analysis. We are concerned here with the free flight sector of the trajectory, which can be treated without any knowledge of the details of the powered flight phase.