Reentry Guidance for Apollo: Volume I

The design of the reentry steering for the Apollo spacecraft is discussed in detail. Error performance is the critical design factor. A great deal of effort has been spent to find a system that would steer properly in spite of navigation errors. The most significant error is in the initial indicated rate-of-climb. To achieve this error performance a computed reference trajectory is used during the critical supercircular phase, with control gains that have been chosen on a statistical basis to minimize the miss distance. The many other factors which affected the design are presented. Some of these are requirements on the trajectory by the heat shield and monitor system, and limitations on the attitude maneuvers by the roll control system fuel. The performance of the automatic self-contained system using a digital computer is presented. Guidance to all possible points throughout the entry corridor is demonstrated. The detailed computer logic for the Apollo Guidance Computer is also presented.