ABSTRACT
A Satellite telescope consists of various components such as primary mirror, secondary mirror, detector unit and metering structure etc. Generally, space borne telescopes are subjected to orbital loads like temperature excursion, absences of gravity, moisture release of metering structure and due to this, there is a change in focal length and misalignment of optical system takes place which ultimately reduces the quality of images. So to get the perfect focal point, it is necessary to reset the distance between primary and secondary mirror by means of re-focusing mechanism. This re-focusing mechanism is placed behind the secondary mirror in order to compensate the change in distance between primary and secondary mirror. In this paper, the design and development of thermal actuator based refocusing mechanism have been proposed. The refocusing mechanism has been designed for ± 10 micron displacement in both forward and backward directions by means of heating only. It also provides six degrees of movement to a secondary mirror. Material for thermal actuator is selected and amount of temperature variation required for specified movement of the mechanism is studied. Experiments are performed in thermo-vacuum chambers and results are validated with structural and thermal analysis using commercially available software.
