Optimum mount location for lightweight mirrors in a gravitational environment with optical axis horizontal

Abstract

Determination of the optimum mount zone to minimize gravitational deformation of mirrors, when gravity is aligned with the optical axis vertical, is well-documented. Less has been written about such optimum zones when such mirrors, particularly lightweight cored optics, are aligned with the gravity axis normal to the horizontal optical axis. An equation is herein presented to determine the optimum axial mount zone to minimize wavefront error in this environment, for powered optics (finite radius of curvature). Generally, for most optical systems, wavefront error is lower in this configuration than in the vertical axis orientation, important for ground test of space-based optics. When mounted at three near-kinematic points, determined is an equation to find ideal axial mount location at any radial mount zone to minimize error and an equation to predict gravitational deformation that bounds all mount zones to conservatively estimate performance error. Optimum zones are found to lie near, but not coincident to, the mirror centroid and/or neutral surface. These analyses allow the engineer to quickly determine first order errors considering design envelope restrictions, prior to more detailed finite element analyses.