Athermal design of nearly incompressible bonds

Selecting the proper thickness of high shape factor bonds using near incompressible adhesives is critical to minimize the elastic response of the bonded optical element. For incompressible adhesives with low shape factor, variations in the bond thickness are shown not to be as critical. This is illustrated in the evaluation and redesign of an RTV bond for a primary mirror of a Cassegrain telescope. The initial bond was oversized and highly constrained resulting in focus errors in the telescope during optical testing. Subsequent redesign of the bond thickness to athermalize the design compared various closed-form solutions and finite element parametric studies.