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Chapter 10:
Techniques for Mounting Metallic Mirrors
The design of metallic mirrors was discussed in Section 8.8 of this work. Because the design of the mirror itself and the design of its mounting are closely interrelated in many cases, examples of a few mountings were also described in that section. For example, Figs. 8.41 showed how the aluminum secondary mirror for the Kuiper Airborne Observatory was attached with screws to the hub of a tip∕tilt drive mechanism. Providing a proper interface between the mirror and the hub and the requirement for minimal weight along with high stiffness so the mechanism could move the mirror at high acceleration rates were key features of the mirror design. Similarly, the mountings for the beryllium primary segments of the James Webb Space Telescope, described in conjunction with Fig. 8.45, are closely tied to the design of the mirrors. In this chapter, we delve more deeply into the specifics of mounting metallic mirrors. First, we consider how metal mirrors and their interfaces with the mountings can be shaped precisely by single point diamond turning. Then, we consider integral mountings wherein features of the mirror substrate are configured to attach directly to the mechanical support. Provision of flexures in the mounting features of larger metallic mirrors is then described. These flexures serve to minimize optical surface distortion effects due to mounting forces. We consider how platings applied to the mirror surfaces to provide suitable material for polishing or diamond turning affect the optical behavior of the mirror when the temperature changes. Heat transfer through the mechanical interface plays a key role in such cases. Finally, we describe how metallic mirrors and their mounts can be configured to facilitate assembly and alignment.
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