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Spinning Wheels at 38K?

Submitter: Ramon Navarro
Description: Exciting times at NOVA-ASTRON these days. We are at the final stages of integration of the Cold Optical Bench for MATISSE; the mid-infrared interferometric spectrograph and imager for ESO's VLT interferometer (VLTI) at Paranal, Chile. Matisse can combine the light from all 4 eight-meter VLT telescopes.

This picture shows the motor bracket for the three filter wheels in the MATISSE Cold Optical Bench. Accurately rotating these wheels in a vacuum cryogenic environment is not straightforward at all. The use of lubrication is not allowed because of contamination of the vacuum. Positioning accuracies are tighter than any motor could deliver, therefore a mechanism with indents is used for positioning while allowing some play on the motor, however this could lead to step loss in stepper motors and consequently control issues. The power dissipation during movement must be minimized, because this heat load causes thermal instabilities in the system. Finally only a few electro motors are qualified for use in cryogenic environments.

On the left of the image you can find the clutches that connect to the filter wheel mechanisms. Then a light tight lid to prevent IR radiation inside the cold optics bench. Further right Phytron #VSS motors (copper wires) with resolvers (colored wires) mounted on the same axis in order to monitor exactly what is happening inside the cryostat.

MATISSE is capable of imaging at spatial resolutions of ~6 milli-arcsec in the 2.8-5 and 8-13 micrometer wavelength range. This enables the study of wavelength-dependent characteristics of gas and dust grains. This includes the formation and evolution of planetary systems, Active Galactic Nuclei and high-contrast environment of evolved stars.
Copyright: Ramon Navarro
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