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 they highlight the importance of accurate polarimetry. The new system will include a fast guider mirror to remove image jitter from wind and mechanical sources. New software, data-control computer, and ancillary electronic systems will completely replace the ancient PDP 11 system.
The conceptual design calls for replacing the existing limb guider/translation stage system 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 to control this 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 '95. The first construction phase of the project was to upgrade the mechanical drive assemblies at the #2 mirror and was completed in November 1995.
Fabrication of the mechanical components of the fast #4-mirror mount was completed in February 1996. Integration and testing of the control electronics and #4-mirror mount is now underway in Tucson. Installation at the telescope of the new mount and control electronics is planned for spring 1996. Procurement of the telescope control computer and limb-guider control hardware is underway. Installation of the new limb guider system is planned for late 1996.
Jeremy Wagner, Harry Jones, Jack Harvey