Digital autopilot for the SKYLAB orbital assembly.

In Project SKYLAB, the Command and Service Module which ferries astronaut crews to and from the Orbital Workshop is required to have the capability of providing attitude control for the entire Orbital Assembly during docked phases of the mission. A digital autopilot has been designed which meets this requirement. It is a direct descendant of the digital autopilot designed for and used extensively in project Apollo. There is a major difference however. For Apollo, it was reasonable to design an autopilot that treated the roll, pitch, and yaw axes independently. Because of the geometry of the Orbital Assembly, however, it is of considerable advantage to design the jet selection logic for SKYLAB such that the roll and pitch axes are treated as coupled, and also that the roll and yaw axes are treated as coupled. This paper discusses how inter-axis dependence has been incorporated in the Command and Service Module's digital autopilot while working within the limitations of the onboard computer.