Gravity unloading of a very large spaceborne monolithic SiC mirror

Abstract

We formulated a gravity unloading strategy for a monolithic silicon carbide (SiC) mirror with a Φ3m aperture in space. Employing the finite element analysis (FEA) technique, a rapid solution analytical approach for determining optimal support forces during gravity unloading is introduced. This method demonstrates enhanced efficiency and accuracy compared to conventional approaches. A quantitative evaluation methodology for the gravity release error, grounded in the minimum-energy mode, is delineated. The adverse impacts could be expeditiously computed by assessing the maximum deflection of minimum-energy modes generated by various errors. The analytical findings revealed that compliance with the stipulated gravity release error criterion of less than 6 nm (root-mean-square) necessitated the gravity unloading force error to fall within the range of ±0.1N. Additionally, the gravity unloading support position error was required to be within Φ0.5mm, and the measurement error pertaining to the rib thickness of the actual mirror blank had to be within ±0.02mm.