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21 February 1986 Thermal Stability Tests Of CFRP Sandwich Panels For Far Infrared Astronomy
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A program for the development and low temperature figure tests of Carbon Fiber Reinforced Plastic (CFRP) sandwich panels has been initiated as a possible solution to the requirements for a very lightweight primary mirror for a three-meter diameter balloon-borne far-infrared and submillimeter telescope. The requirements for the mirror are that it have a one to two micron rms surface figure accuracy, that it be very lightweight (approximately 10 kilograms per square meter), that it maintain its figure at an operating temperature of -40 to -50 degrees Centigrade, that it rapidly reach thermal equilibrium after a two hour ascent through the tropopause to the operating termperature at 30 kilometer altitude, and that it survive the acceleration forces during the launch, the parachute opening, and the landing. The CFRP sandwich panel readily meets the lightweight, thermal conductivity, .cp 11 and durability requirements. Figure accuracy achieved with current techniques replicating against a precision ground convex Pyrex mold are 2-3 microns rms, close to the required one to two microns. Optical figure measurements on the first two of a series of four .5 meter test panels replicated to a spherical surface with a radius of curvature 10 meters, show large-scale focus (radius of curvature) change and astigmatism down to temperatures of -60 degrees Centigrade which follow approximately the theoretical prediction for the composite. All other deformation at -60 degrees is less than 1 micron rms. These results indicate that the material and process control is excellent and that with appropriate design changes in the lay up, the large-scale changes can be compensated for. Further tests are being carried out to demonstrate this hypothesis.
© (1986) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
William F. Hoffmann, Gunter Helwig, and Dietmar Scheulen "Thermal Stability Tests Of CFRP Sandwich Panels For Far Infrared Astronomy", Proc. SPIE 0571, Large Optics Technology, (21 February 1986);

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