Design and Optimization of Ultra-Stable Fine-Pointing Structures for the CHIME Instrument

CHIME (Copernicus Hyperspectral Imaging Mission for the Environment) is part of ESA’s Sentinel Expansion Program for which OHB System AG in Oberpfaffenhofen, Germany has been selected as the instrument prime contractor. In this paper we present the development of the ultra-stable stiffness architecture for the instrument structure. Backed by a trade study of different structural concepts with a focus on the opto-mechanical decoupling, assembly integration and test accessibility, and the demanding optical performance criteria, we derive a robust solution: The main stiffness element is a central monolithic CFRP (Carbon Fiber Reinforced Plastic) torus, on which several sub-elements are mounted for precise positioning of the highly-sensitive optical elements, creating a modular 3D optical bench. We demonstrate the use of topology optimization for design concept finding considering mass and performance criteria. The paper concludes with the results from a breadboard test campaign and an outlook on the next development steps.