Spaceborne Tilt Mirror Mechanism and Application of Shape Memory Alloy Actuator to Implement Fail-safe Function in Emergency Mode

Shape memory alloy (SMA) actuators have been widely used for space applications. We used a SMA actuator to implement a fail-safe function on a tilt mirror mechanism for the on-board calibration of a spaceborne imaging sensor. The proposed mechanism prevents the blocking of a main optical path when the tilt mirror is stopped at a certain position during calibration. In the present work, the operation concept of tilt mirror, design, and functional test results of the tilt mirror mechanism have been introduced. The test results demonstrate that the proposed tilt mirror mechanism achieves all of the required deploying and stowing functions for on-board calibration. The use of a shape memory alloy actuator is shown to be effective for application to the fail-safe function of a mechanism driven by a geared stepper motor.