Monitoring lap forces during final polishing of the MMT 6.5-m honeycomb mirror

Abstract

The new 6.5-m honeycomb mirror for the Multiple Mirror Telescope Observatory on Mt. Hopkins was polished with a 1.2-m stress lap on the Large Optical Generator at the Steward Observatory Mirror Lab. Problems during the last few months of polishing led to the development of a system for monitoring the drag forces on this lap. Records of the drag forces during each stroke were then used to compute an effective drag coefficient as well as the frictional power dissipated per unit area of mirror as a function of radius. While the glass removal rate was found to track the observed distribution of expended frictional energy quite nicely, the system turned out to be even more valuable as a tool for identifying anomalous drag conditions before they put a significant imprint on the mirror.