Novel CTE Tuning of Ultra-Stable ALLVAR Alloy Struts for Large Space Telescopes

ALLVAR Alloys-30 shrinks when heated and expands when cooled, known as negative thermal expansion (NTE). This opposite effect from most materials allows Alloy-30 to compensate for positive thermal expansion (PTE) materials. We have created a new material for athermalizing optics made from any type of mirror material by joining Alloy-30 to other PTE metals to create a specified thermal expansion coefficient. Currently, achievable coefficients of thermal expansion (CTE) range between -30 ppm/K, Alloy-30rsquo;s CTE, to +24 ppm/K, Aluminumrsquo;s CTE. This provides a new alternative material to currently used carbon fiber composite metering structures and trusses used in optics. The pm-stability of these new metal structures have already been achieved. If this new technology can be scaled to have ultra-stability at meter length scales and the CTE tuned to within ppb/K, they could be used as metering structures in EUV/Optical/IR large area telescopes. The novel CTE tuning method has the potential to simplify the manufacturing and alignment and offer greater thermal stability of these optic systems.