Abstract
In this study, a multispectral spaceborne Cassegrain telescope was developed. The telescope was equipped with a primary mirror with a 450-mm clear aperture composed of Zerodur and lightweighted at a ratio of approximately 50% to meet both thermal and mass requirements. Reducing the astigmatism was critical for this mirror. The astigmatism is caused by gravity effects, the bonding process, and deformation from mounting the main structure of the telescope (main plate). This article presents the primary mirror alignment, mechanical ground-supported equipment (MGSE), assembly process, and optical performance test used to assemble the primary mirror. A mechanical compensated shim is used as the interface between the bipod flexure and main plate. The shim was used to compensate for manufacturer errors found in components and differences between local coplanarity errors to prevent stress while the bipod flexure was screwed to the main plate. After primary mirror assembly, an optical performance test method called a bench test with an algorithm was used to analyze the astigmatism caused by the gravity effect and deformation from the mounting or supporter. The tolerance conditions for the primary mirror assembly require the astigmatism caused by gravity and mounting force deformation to be less than P−V0.02 λ at 632.8 nm. The results demonstrated that the designed MGSE used in the alignment and assembly processes met the critical requirements for the primary mirror assembly of the telescope.
Highlights
A coordinate measuring machine (CMM) is a rapid, flexible, and capable tool, which can measure the dimensions, forms, and positions of geometric objects
The results indicated that the mechanical ground-supported equipment (MGSE) designed for the alignment and assembly processes met the critical requirements for primary mirror assembly of the telescope
A CMM is an excellent tool to assist with aligning the primary mirror with respect to the main plate and aligning the bipod flexure to the correct bonding position
Summary
A coordinate measuring machine (CMM) is a rapid, flexible, and capable tool, which can measure the dimensions, forms, and positions of geometric objects. It can be used in optical assembly processes to compare the assembly result with the design tolerance. The relative positions of the features that are in the reference frame of the machine and the reference frame based on the previously measured features of the object can be calculated.[1] Certain tolerances of optomechanical subassemblies, such as the curvature radius, thickness, air space, decenter, axial translation, tilt, and roll,[2] can be derived by a precision CMM. A Leitz CMM was used to develop the James Webb Space Telescope to control the radius of curvature, conic constant, and
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