Gravity effects and damage detection for truss-type spacecraft

Analytical and experimental verification studies of damage detection using vibration testing for application to truss-type spacecraft have been previously accomplished without considering the effects of gravity. Comparison of recent ground and on-orbit tests illustrates gravity influences on the vibration response of truss-type structures and provides understanding of gravity effects. With this understanding, we are in a position to evaluate on-orbit damage detection based on vibration measurement considering gravity effects. In this paper, two gravity effects are considered analytically - static deformation in the 1-G environment and joint destiffening in the on-orbit environment. Two structures are also considered - the 8-bay truss structure that has been employed in ground experiments for damage detection verification and the MODE truss structure which has been employed in ground and on-orbit experiments for vibration test verification. Both effects are found to be small in comparison with the effect of catastrophic failure of an element of the truss, thus allowing, in general, for successful damage location. However, the analytical model used in the damage detection analysis was found to be a significant influence.