NASA Tech Briefs - November 2008
Two-Stage Passive Vibration Isolator
NASA's Jet Propulsion Laboratory, Pasadena, California
The design and testing of a structural system were implemented to hold the op lies of the planned Space Interferometry Mission (SIM) at positions and orientations characterized by vibrational translation and rotation errors of no more than a few nanometers or a few milliarcseconds, respectively. Much of the effort was devoted to a test bed for verifying the predicted behavior of a vibration-isolation struc¬tural subsystem working together with an active control system for positioning and orienting the SIM optics.
There was considerable emphasis on the vibration-isolation subsystem, which was passive and comprised two stages. The main sources of vibration were six reaction wheels in an assembly denoted the "backpack." The first vibration-isolation stage consisted of hexapod isolator mounts — one for each reaction wheel — characterized by a natural vibration frequency of 10 Hz. The second stage was a set of three beams, disposed between the backpack and the structure that held the SIM optics, that were flexured such that they transmitted only bending loads, with a natural vibrational frequency and damping of about 5 Hz and 4 percent, respectively.