SpaceTech has developed a motor driven ultra-fine refokus mechanism providing a robust design, comfortable and stable pointing operations with ultra-high pointing accuracy and stability. The mechanism can be used in all areas in which a linear displacement movement between two parts with high accuracy over a relatively long travel distance is required.
It finds an important, although not exclusive application in actuators that move a secondary mirror of an optical telescope between two positions in order adjust the focus of the overall optical system. Particularly with space telescopes, misalignments of the optical units that occur by mechanical settling effects from the launch, thermal effects or moisture release of the satellite structure can effectively corrected in space. Thus by using one or multiple REFOC-MD actuators it is possible to significantly improve the image quality of i.e. earth observation optical instruments.
The mechanism features a robust design providing:
- Stepper motor drive with redundant wiring
- High position accuracy and stability
- Zero power demand to maintain a fixed position
- Small envelope and low mass
- Comfortable torque margin
- Embedded launch lock device
- Redundant end switches and additional mechanical end stops
Only dry lubricants are being used to avoid contamination of sensitive optics and to avoid the need for special maintenance.
Breadboard tests have been performed to determine the difference between the commanded and actually achieved actuator positions. The recorded deviations were all in a range below 0.2 μm. With a given statistical accuracy of the actuators of 0.1 μm an overall 3σ accuracy of 0.3 μm for the actuator positioning is granted.