Nanometer-Scale Spontaneous Vibrations in a Deployable Truss Under Mechanical Loading

Abstract

Evidence is reported of spontaneous vibrations of a deployable spacecraft structure at optical levels of motion under mechanical loads. In these experiments a truss was mechanically loaded while in a thermally and vibrationally stabilized test environment. The applied loads were smaller, by a factor of 20, than the load that would have caused gross slippage in the frictional interfaces of the structure. Even so, results indicate that infrequent, spontaneous vibrations occurred. Most of these vibrations occurred after the application and removal of a mechanical load. The response spectra of the vibrations occurred in narrow bandwidths around the dominant modal frequencies of the structure. The vibrations ranged in amplitude from 4 to 20 nm and in velocity from 2 to 8 μ/s. Potential error sources are eliminated, including unmeasured environmental excitations and sensor errors. These vibrations are presumed to arise from the sudden release of strain energy stored in the hysteretic mechanisms and materials of the structure. An analysis based on this hypothesis shows that the amplitude of the observed vibrations is quantitatively consistent with this theory.