For the on-ground calibration setup of the SAFARI instrument cryogenic mechanisms are being developed at SRON
Netherlands Institute for Space Research, including a filter wheel, XYZ-scanner and a flipmirror mechanism. Due to the
extremely low background radiation requirement of the SAFARI instrument, all of these mechanisms will have to
perform their work at 4.5 Kelvin and low-dissipative cryogenic actuators are required to drive these mechanisms.
In this paper, the performance of stepper motors, piezoelectric actuators and brushless DC-motors as cryogenic actuators
are compared. We tested stepper motor mechanical performance and electrical dissipation at 4K. The actuator
requirements, test setup and test results are presented. Furthermore, design considerations and early performance tests of
the flipmirror mechanism are discussed. This flipmirror features a 102 x 72 mm aluminum mirror that can be rotated 45°.
A Phytron stepper motor with reduction gearbox has been chosen to drive the flipmirror. Testing showed that this motor
has a dissipation of 49mW at 4K with a torque of 60Nmm at 100rpm.
Thermal modeling of the flipmirror mechanism predicts that with proper thermal strapping the peak temperature of the
flipmirror after a single action will be within the background level requirements of the SAFARI instrument. Early tests
confirm this result. For low-duty cycle operations commercial stepper motors appear suitable as actuators for test
equipment in the SAFARI on ground calibration setup.
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