Effects of Ply-level Imperfections and Space Environment on Bistability of Ultrathin Composite Booms

Ultrathin composite tape-measure-like booms with an antisymmetric laminate layup can be designed to exhibit two stable equilibrium states: a coiled configuration and a deployed one. This bistable characteristic serves as the basis for designing coilable and self-deployable spacecraft booms. In this paper, we present theoretical and numerical studies on the effects of ply-level imperfections and space environment on such bistability. The influence of uniform ply thickness defects was investigated using the classical lamination theory. Thickness defects add coupling between bending and twisting, which affects the characteristics of the coiled configuration: it coils at an angle, creating a twisted helical structure, and its energy is increased which could facilitate deployment. The effect of defects of ply angle was also studied. Overall, the coiling radius is decreased when the ply angle is increased, leading to a tighter but helicoidal coiled configuration. The strain energy was then modified to consider residual bending moments due to thermal effects. Uniform temperature variations across the boom led to a loss of bistability for temperature differences higher than 25°C, and to a loss of compactness due to twisting of the coiled configuration otherwise. Different temperature conditions can also be applied to each ply to consider non-uniform temperature distributions through thickness direction in the boom. The stability of the boom depends on both the amplitude and profile of the temperature gradient.