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.

Calibration mirror mechanism has been widely used for on-board calibration with black body. The calibration mirror is deployed to reflect the radiation energy from the black body to the image sensor for calibrating the sensor system. After the calibration, the calibration mirror is stowed not to hide a main optical path. It also has a fail-safe function which can stow the mirror by just removing the input power of motor when the calibration mirror is stopped at certain position during the calibration. In the present work, the operation concept, design, torque analysis and functional test results of the calibration mirror mechanism with the aforementioned function have been introduced and investigated.