Active correction of wind-buffeting deformations of thin telescope primaries in the extended active optics bandpass

Details Active correction of wind-buffeting deformations of thin telescope primaries in the extended active optics bandpass Active correction of wind-buffeting deformations of thin telescope primaries in the extended active optics bandpass

Oct 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993pasp..105.1175w&link_type=abstract

Astronomical Society of the Pacific, Publications (ISSN 0004-6280), vol. 105, no. 692, p. 1175-1183

Physics

Optics

1

Optical Correction Procedure, Optical Measuring Instruments, Telescopes, Wind Effects, Bandwidth, Buffeting

Scientific paper

Wind buffeting can produce deformation of thin meniscus primaries, above all for large sizes. At low temporal frequencies, below 1/30 Hz, these deformations can be monitored and corrected by the normal closed-loop active optics system using a natural star in the field as reference. However, the temporal frequency bandpass of wind-buffeting deformation can extend into the extended active optics bandpass (1/3 to about 10 Hz). In this bandpass, a natural star near the edge of the field gives wrong information for the field center because of overlap with the atmospheric bandpass and the limitation of the isoplanatic angle. An independent detection system for this bandpass is therefore required. This paper reviews the possibilties for an independent detection system. We conclude that the most promising are a group of optical detection systems operating from the front face of the primary. The application is considered for the Eurpoean Southern Observatory (ESO) VLT 8 m primaries with an aspect ratio of 47. Some of the front surface detection methods discussed may also be highly relevant to the active control of radio telescopes. The front detection systems can also detect the influence of 'tube seeing' in a functional arrangement, i.e., on-line during observing. Correct measurment of the errors induced by wind buffeting of primaries is an esential prerequisite to their active correction. The design of actuators to achieve this correction is a separate technical issue not treated in this paper.

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