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A New Guider and Control System for the Kitt Peak Vacuum Telescope (1Mar96)
(from NSO, NOAO Newsletter No. 45, March 1996)

As part of an NSO-wide program to improve image quality, the
replacement of the 22-year old control and guiding system of the NSO/KP
Vacuum Telescope is underway. The maintenance of the current system has
become difficult, and the guider no longer functions properly in some
operational modes or in light clouds.  Recent magnetograph comparisons
indicate that spurious image motion is a serious problem for overall
magnetic calibration and highlight the importance of accurate
polarimetry. Thus the new system will also include a fast guider mirror
to remove image jitter from wind vibration and mechanical sources. The
software, data control computer, and ancillary electronic systems will
be completely replaced to eliminate the ancient PDP 11/73/FORTH/CAMAC
system.

The conceptual design calls for replacing the existing limb
guider/translation stage system at the KPVT with a modern system
coupled to a fast guider mirror. Image motion compensation will be done
by remounting the #4 mirror so that it can be tilted rapidly. The error
signal for control of the mirror will be derived from motion of the
guider image. The servo loop will be closed by means of an existing
laser system that locks the main and guider beams together. The motion
compensation phase of the KPVT upgrade is partially supported by NASA.

Engineering tests to confirm the feasibility of the jitter compensation
design were completed in early FY 1995. The first construction phase of
the project was to upgrade the mechanical drive assemblies at the #2
mirror and was completed in November 1995. The fabrication of the
mechanical components of the #4 mirror mount is nearly complete.
Installation of the new mount is planned for early spring 1996. The
electrical, mechanical, and software designs for the guider are
expected to be complete and ready for fabrication and coding by early
summer 1996.

Jack Harvey, Harry Jones, Jeremy Wagner

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