Lunar module digital autopilot

The lunar module digital autopilot is a first generation digital control system which would have been difficult to implement with conventional analog autopilot design techniques. The control synthesis problem was divided into the design of an attitude state estimator, the reaction-control-system (RCS) control laws, and the main engine thrust-vector control laws. The attitude state estimator derives the angular velocity and angular acceleration of the vehicle, based on measurements of vehicle attitude and assumed control response only. Rate gyros are not used. The RCS control laws employ parabolic switch curves in their phase plane logic to obtain fast response with a minimum of firings. The critical parameters are adapted in flight in response to varying flight conditions. An unconventional set of nonorthogonal axes is used to decouple the responses to RCS control about different spacecraft axes. A thirdorder minimum time control law is used to control the vehicle attitude by means of the thrusting descent engine. Performance in flight is presented.