Preliminary Study of a Shape Reconstruction Sensing Architecture for Space Applications

This paper focuses on the preliminary investigation on a shape reconstruction architecture for a CFRP grid structure without skin (a lattice shell structure), conceived for space payload applications. The object of the study, in particular, is represented by a slender cylindrical shell of a boom segment for deployable antennas. It is characterised by minimum mass design, adequate dynamic stiffness, and rather strict thermal stability requirements. Indeed, the typical operational scenario of the component foresees large thermal excursions and different exposition to the solar radiation with consequent thermal gradients that may arise both in longitudinal and radial directions. The radial gradient, in particular, causes asymmetric distortions and deflections of the boom segment that alter the nominal position of the tip of the structure, with unfavourable effects on the steering accuracy. However, a subsystem capable to measure and reconstruct the actual shape may play a fundamental role, both for quantifying the deviations from the nominal condition (a position error lower than 0.15 mm is allowed on the tip of the structure, 3 m long) and for driving future active distortion recovery systems. Two FEM structural models (1D and 3D) are available for the boom segment demonstrator, in order to highlight the most deformed areas. To this scope, the areas in which the deformation signal is greater have been identified, with the aim of linking relevant strain field to the displacement of the free end towards axial and transversal directions. On the basis of a critical analysis of the results, a minimum number of sensors was identified and their exact position determined. The estimated strain field was then organised in a suitable format and elaborated through a MATLAB code. With a zero ideal a measurement error a stable solution was obtained. When a measurement error of about 1% was introduced on the sensors, the deviation on the estimate of the tip displacement was quantified, highlighting strength and weak points of the approach. Further investigation will be addressed to mitigate the effects of measurement errors through a certain redundancy of the logic and to handle additional phenomena such structural instabilities or material non-linearities.