Low-Power Shutter Mechanism for a Cryogenic Infrared Camera

An assembly that includes electromechanical rotary actuators has been developed specifically for use as the shutter mechanism of a cryogenic infrared camera that will be part of an astronomical telescope. The camera will be cooled, by use of superfluid helium, to an operating temperature of 1.4 K. On command, the shutter mechanism rotates a mirror to one of two angular positions, denoted open or closed, at opposite ends of a 38° arc (see Figure 1). When the mirror is in the open position, light gathered by the telescope proceeds unobstructed to the focal plane of the camera; when the mirror is in the closed position, it obstructs the incoming light and provides a dark environment for calibration of the infrared photodetectors in the camera. The shutter mechanism is designed to be rugged, to have relatively low mass (<1.6 kg), and to satisfy several requirements that pertain to mechanical and electrical performance in the cryogenic environment. A primary requirement is that the power dissipation averaged over time not exceed 5 mW.