Structural behaviour of pre-tensioned solar sails

This paper presents an experimental and computational study on the behaviour of pre-tensioned thin solar sails. Firstly, a set of experimental tests of thin rectangular sheets made of Kapton® subjected to uniaxial tension were conducted to characterize the mechanical properties of the membrane. Then, tri-dimensional digital image correlation technique was used to capture the evolution of the wrinkling (shape and amplitude) in pre-tensioned specimens, a phenomenon that often affects the serviceability of solar sails. The influence of membrane thickness and specimen dimensions on the wrinkling behaviour were also studied. Next, nonlinear finite element models were used to simulate the membranes and to study the onset and growth of wrinkles in solar sails. First, by pre-tensioning the membrane with truss cables and using combinations of the eigenmodes extracted from buckling analysis as the membrane initial geometrical imperfections, nonlinear analyses were performed. The computational methodology was verified by comparing the experimental results of membrane specimens with those obtained from finite element analysis. Because the number of truss cables that pre-tension the solar sail plays a key role in their behaviour, two distinct configurations were considered: (i) five points connected sail and (ii) multiple points connected sail. Sensitivity studies were performed, including the influence of (i) membrane size and (ii) pre-tensioning magnitude on the solar sail wrinkling. Larger sails exhibit higher wrinkle dispersion and amplitude. Higher pre-tensioning induces more wrinkles, higher amplitudes and lower wavelengths. The solar sail configuration with multiple connected points connected presents less wrinkles with lower amplitude, and it is preferable to the configuration with five connected points. Finally, it was revealed that the wrinkling maximum amplitude varied approximately in a power law with the pre-tensioning level.