ALLVAR alloy athermalization: a novel and cost-effective alternative for small to moderate sized space telescopes

Design To Unit Production Cost (DTUPC) is of crucial importance to the viability and implementation of constellations which require tens to hundreds of small to moderate sized spaceborne telescopes (10-cm to 50-cm aperture). Emerging technologies enable cost-effective alternatives to the traditional design and build of such telescopes. This is especially true for the structure of Optical Telescope Assemblies (OTAs) addressing environments where orbital phase modulated thermal gradients and transients dominate design. The implementation of a dimensionally stable structure is crucial to the performance of a telescope, and typically, compensation with focus mechanisms is not a cost-effective option in this size. ALLVAR Alloys, a family of emerging aerospace materials exhibiting Negative Thermal Expansion (NTE), can offer novel and cost-effective approaches to OTA metering. These Titanium-based alloys' NTE can be used to dial in a specific thermal expansion or zero expansion profile by compensating for the natural expansion of other telescope components. For the first time, a telescope designer can passively control thermal stability of a telescope's metering/support structures. This is true both for designs based on materials with low or high Coefficients of Thermal Expansion (CTE) and low or high thermal diffusivity (for example ULE®, ZERODUR® or ClearCeram metered with CFRP and Invar vs. all Aluminum or all SiC approaches). NTE ALLVAR Alloys offer a brand-new solution for athermalizing telescope structures and offer several benefits over Invar and CFRP including lower cost, faster lead time, and greater thermal stability control in modulated orbital thermal environments.