Microdynamic characterization of modal parameters for a deployable space structure

Results are presented from an experimental investigation of the microdynami cs of deployable space structures. The dynamic response of a representative deployable truss at submicrostrain levels of vibration was characterized i n terms of modal parameters. The test article was subjected to stepped-sine sweeps through its fundamental flexible modes over a range of excitation a mplitudes. High-sensitivity piezoceramic strain sensors were used in conjun ction with a lock-in amplifier to measure the truss response from tens of m icrostrain down to one nanostrain. The results show that the values of moda l frequency and damping ratio are strain dependent at high response amplitu des and strain independent at low amplitudes. It is inferred that, at micro dynamic Levels of excitation, the internal loads needed to overcome the joi nt friction are not attained. The nonlinear mechanisms in the deployable st ructure are, thus, not activated, resulting in a linear truss response.