Rationale for Defining Structural Requirements for Large Space Telescopes

Abstract

The present paper presents a rationale for defining structural requirements for future large space telescope systems. The rationale is based on bounding analyses for the deformation of telescope mirrors in response to expected on-orbit disturbance loads and consideration of active control systems that partially compensate for these deformations. It is shown that the vibration frequency of the telescope structure, independent of telescope size, determines the passive structural stability and requirements for an active control system. This means that future large telescopes with low vibration frequencies will necessarily allocate increased active control error budget in proportion to the square of the vibration frequency. Parametric analyses are also presented for the vibration response of two representative mirror architectures: a tensioned membrane mirror and a truss-supporte d segmented mirror. These examples demonstrate that meeting a specified frequency requirement will require a trade between structural mass fraction and depth of the primary mirror support structure regardless of the structural architecture.