On-Orbit Investigation of Transient Microdynamic Disturbances on a Deployed Truss Structure

The second Interferometry Program Experiment (IPEX2) is a technology demonstration precursor to the Space Interferometry Mission, a 10-meter baseline spacebased interferometer scheduled for launch in 2005. The main objective of the IPEX-2 flight experiment is to ascertain the existence of transient disturbances originating within mechanisms, joints and materials, due to sudden internal strain energy redistribution. Results from this on-orbit microdynamic investigation of a representative deployed truss structure are presented, along with a summary of the finite element modeling work performed on the IPEX-2 structure. The experimental results demonstrate the existence of broadband transient disturbances believed to have resulted from thermallyinduced vibrations in the structure (thermal creaks). A quantitative characterization of these disturbances is performed, revealing peak acceleration response levels between 300 pg and 700 pg, in general. The corresponding peak integrated displacements are generally less than 50 nm in amplitude. Microdynamic response to known disturbance sources such as flight data recorders, gyros and thrusters are also characterized.