The current design base of the Space Shuttle Orbiter employs hydraulic actuation for control of aerosurfaces, engine thrust, engine thrust vector, brakes, and landing gear functions. As early as 1972, electromechanical actuation (EMA) was considered as an alternative system. As a result of continued advances in technology development, studies now indicate that EMA is a more attractive alternative. Major advantages are weight reduction, striking improvement in energy efficiency, easier maintenance, and a cleaner vehicle.
The results of a system study advocating EMA for the Orbiter are presented. Emphasis is placed on a clear understanding of the relationships between mission requirements and design parameters. EMA system energy requirements are compared with those of the existing hydraulic system. Detailed discussion of the synthesized EMA system is limited to the aerosurface actuators. The design is consistent with the Orbiter “fail operational,” “fail safe” redundancy requirement. Finally, an assessment summary of EMA for Orbiter is made.