ABSTRACT
Most of the topics considered so far in this book have dealt with the individual components and subassemblies of an opto-mechanical instrument. We have discussed component interrelations and interfaces with regard to certain types of devices, but have touched only lightly on how these parts are held together to form a complete optical instrument. This chapter addresses some important structural aspects of instrument design and discusses selected examples illustrating typical kinds of constructions. We begin with the consideration of designs with rigid housings made of materials such as cast aluminum. This structural configuration serves as a baseline for the design of most optical instruments. Each subsequent example involves some unique structural feature that distinguishes it from the baseline construction. Our discussion of basic structural configurations of optical instruments continues with descriptions of several instruments with modular construction and one with a structure designed to fail gracefully under high shock. A major portion of this chapter is devoted to discussions of athermalization of instruments, including reflecting systems featuring uniform thermal expansion characteristics and ones with metering rods or trusses to compensate for temperature effects on axial spacings between mirrors. Key principles for athermalizing refracting optical systems are also outlined. We close with considerations of various types and geometries of truss structures for ground-based and spaceborne telescope applications.
