The need and desire for large-scale reflectors is immediate and long lasting. Therefore engineers and designers are turning toward processes that produce reflectors much different than the conventional ground glass mirror. This paradigm shift encompasses many new and emerging technologies, including, but not limited to, pressure-augmented stress-coated membrane mirrors.
Recent research has centered on determining the proper amount of stress (from the coating) to apply to a membrane substrate to produce a near-net shape that can be augmented with positive pressure to conclude in the smallest figure error. The bulge test has been applied to membrane samples of seven inch diameter, both uncoated and after coating, and central displacements used as data points when coupled with the finite element code ABAQUS to determine strain and stress values. These values are then correlated to the coating process to determine a 'coating prescription' by which that state of minimal figure error can be attained.
Vibration testing in vacuum also shows promise as an effective method to determine the amount of stress present in the coated membrane. The shifts in natural frequencies of a coated membrane versus its uncoated self are unique and indicative of the stress increase by the addition of the coating. These natural frequencies are input into theoretical and ABAQUS models to determine strain and stress. This method is used to provide confidence with the bulge test results.
This paper continues the work of a previous paper by investigating the concept of an initially parabolic membrane that is "flattened" due to intrinsic stresses and then re-inflated. The pressure to obtain zero apex displacement is determined, and root mean square (RMS) error is calculated. The RMS error is then minimized by varying the pressure. We also investigate the frequency response of a support ring connected to such a membrane. It is shown that the compressive loads applied by the membrane do not change the natural frequencies of the support ring appreciably.