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Reflectors for radiotelescopes are made of numerous segments, called panels. Typical diameters of radio telescope reflectors are 3 to 25m (10ft to 75ft). To receive 0,8mm wavelength the allowable tolerance of the reflector is roundabout 0.05mm. Single panels should have tolerances <10 Micrometer RMS. To achieve tight tolerances as these with relatively big and flat parts only an absolute minimum of residual stresses in the raw material and after each process step is allowed. BOEHM machines special alloys with highly sophisticated milling strategies. Before we started to machine radio telescope panels, we had years of experience with different big, precise aluminum components. We control the complete production process from casting the alloy, subsequent heat treatments until the product is finished.
Quite important is the long term stability of the machined parts. If panels in use change their form, the properties of the instrument degrade. So, not only lowest residual stresses but also thermal stability is required. Ageing of the material and changing dimensions due to precipitation processes in the material have to be avoided. Chemical treatment to reduce residual stresses is possible.
Until now panels for radio telescop reflectors have been produced from aluminum alloys. BOEHM produced prototypes of magnesium alloy panels. Magnesium alloys have the advantage of a 33% lower density over aluminum alloys. The picture shows a magnesium panel with high stiffness, high precision and low weight. Surface treatment is possible with different approved technologies. Finishing of the reflector surface to closest tolerances is done in cooperation with the LFM, Bremen.
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