Lightweight Deployable Booms: Design, Manufacture, Verification, and Smart Materials Application

Abstract

Large deployable lightweight structures development plays a key role for a number of future space applications such as large antenna reflectors, instrument or gravity gradient booms, and deployable sunshades or as supporting structure for Solar Space Power Systems (SSPS). Solar Sail spacecraft development imposes the utmost strongest requirements on the deployable structure design regarding the best compromise of functionality and deployment reliability as well as extreme lightweight demands, the structural performance, and finally the costs. Solar Sail technology development represents, therefore, an important step towards the establishment of future very large-scale space structures by the provision of building block technologies like deployable lightweight booms. The DLR Institute of Structural Mechanics is developing deployable Carbon Fibre Reinforced Plastics (CFRP) booms in the framework of a joint Solar Sail in-orbit demonstration project, currently being initiated by ESA and DLR on base of a successful ground demonstration. These booms can be coiled around a central hub in a collapsed state for stowage and recover their full structural performance during the deployment in space by self-expansion. The related development work encompasses a wide range of design and lightweight optimization techniques, probabilistic structural analysis, low-cost manufacturing aspects, prototype manufacturing, testing, as well as the establishment of verification methodologies. A general problem of very light and flexible structures is also considered by the present boom design: stability is difficult to be maintained under all operational events such as thermal loading or dynamic oscillations. Passive as well as active means of shape control have been applied to the boom design. Beside structural reasons the CFRP set-up is arranged to allow for a minimum thermal deflection while irradiated asymmetrically. Furthermore, the application of smart materials in terms of piezo ceramic actuators has been successfully development tested on shortened boom samples in exited cantilever beam configuration. A significant reduction in boom tip deflection could be measured, demonstrating generally the suitability of the adaptive technique to comply with tight physical envelope requirements of potential boom applications. The paper reports on the boom development work and its related tasks of design, thermal and structural analysis, low-cost prototype manufacturing, and verification testing. It clearly points out the way to a potential application in space by cross-links to the present ESA/DLR Solar Sail in-orbit demonstration project.