IRESA ‐ Intelligent Redundant Spacecraft Actuator

Over the past decade, the figures of merit of volume and mass for satellites have increased dramatically while the time to orbit decreased in the same manner. New applications based on small satellites are drivers in this new era where spacecraft development has to be both fast and reliable. Deployment and pointing mechanisms are one keystone for future commercial as well as scientific missions. Thus, future spacecraft actuators need to combine reliability with adaptability, while ideally being low power and low mass devices. IRESA (Intelligent, Redundant Spacecraft Actuator), currently under development at the Technical University of Munich in cooperation with the FGW Forschungsgemeinschaft für Werkzeuge and Werkstoffe e.V., is an actuator for pointing mechanisms on small satellites based on shape memory alloys (SMA). IRESA is based on the extrinsic two-way SMA effect. One of multiple parallel SMA-wires is heated electrically, effecting in its contraction. The linear motion is then transformed into rotation for pointing or used directly in hold-down and release applications. The mechanism resets via a mechanical spring. In case of a broken or otherwise dysfunctional SMA-wire, a parallel wire takes over. IRESA enables solar array alignment, pointing of payloads and antennas and easily resettable hold-down and release mechanisms. The actuator's modular design helps to keep the qualification effort and project risks for small satellites at a minimum, while being adaptable in required accuracy, reliability, torque and range. Compared to its classical counterparts, IRESA offers a higher force to mass ratio and simpler design with less components. This paper consists of three parts; in the first part, we will present the concept for the modular actuator and its implementation in a first demonstrator. Performance values of the actuator, including mass, volume, power consumption and achievable torque are given. In the second part, we will present test results from more than five months of qualification testing, covering thermal vacuum performance, shaker and endurance tests. The third part focuses on a method to judge and predict fatigue of the SMA-wire based on intrinsic measurements, enabling both preflight assessment of the actuator age and preventive maintenance during operations. Reliability and adaptability are two cornerstones for future small satellite missions. IRESA is meant to fulfill these goals, while keeping complexity at a minimum through a modular design.