Development of space active optics for a whiffletree supported mirror.

The requirements of a lightweight primary mirror for large-aperture space telescopes include a precise mirror figure and high reliability. However, lightweight mirrors are easily affected by environmental disturbances, as they lack structural stability and rigidity. Active optics can be used to compensate for the gravity-induced deformation and correct low-order aberrations due to thermal changes and gravity relief during observing periods. Due to their complexity, active optics have been rarely used in space. To validate the technology of space active optics, an active optics system based on a passive, whiffletree-supported mirror is developed. During integration and testing on ground and under normal conditions in space, the surface accuracy is guaranteed by passive support. Within this hybrid support, the active optics system only serves to assist support. This paper focuses on the compatibility between a passive multisupporting system and active optics. We present the prototype of a 0.676 m diameter passive supported lightweight mirror and active support with nine axial force actuators. The passive support includes a 9-point axial support and three A-frame lateral support. The active actuator distribution has been optimized with finite element analysis and its experimental performance characterized in representative conditions. The effectiveness of the hybrid passive-active support developed has been verified.