Vibration Isolator for Large Space Telescopes

A full spacecraft vibration isolator for the James Webb Space Telescope is described. This 1-Hz isolator brings wavefront errors and line-of-sight pointing jitter induced by reaction wheel and cryocooler compressor disturbances down to below a few nanometers and milliarcseconds, respectively. The isolator consists of four passively damped beams connecting the corners of the spacecraft to a thermal isolation tower positioning the telescope. An efficient analysis approach was developed based upon a fractional derivative model of the viscoelastic material. The technique employs modal data from a finite element model for a constant operating temperature and frequency. The modal properties are adjusted using frequency- and temperature-dependent properties from the viscoelastic material’s constitutive model. Development test results for the unit isolator elements are presented and compared to model predictions. Results of a dynamic test on an assembled isolator are also presented. The test employs a simulator replicating the full mass and inertia of the telescope. A series of modal surveys was performed across the operating temperature range to validate model predictions.