During optical testing of the James Webb Space Telescope (JWST), ground support equipment will be subjected to
seismic and facility disturbances. Random Power Spectral Density functions developed from acceleration time history
data acquired at Johnson Space Center in August of 2005 are used as the input disturbances. A linear dynamics Finite
Element (FE) model has been constructed in order to produce numerical predictions for various optical outputs (e.g.,
Line Of Sight (LOS), figure vibrate, relative motions) caused by the random disturbances. The numerical simulation
performed is a base shake analysis, where the motions of all ground interface degrees of freedom are slaved together in
magnitude and phase. As the required LOS error for a successful test is highly dependant on the pointing of the primary
mirror, concern arose regarding the effect of uncorrelated disturbances at multiple ground interfaces of the support
equipment over the analysis bandwidth. This paper investigates the differences in LOS predictions from applying a
uniform, combined disturbance at a centralized base location against using mutually uncorrelated acceleration
spectrums at each of the ground interfaces.
In precision optical testing, it is desirable to provide a unified metering structure between the optical test source and the test article to limit the effects of incoming vibration sources. In this manner, the entire optical test structure may be vibration isolated as a single unit. Cryogenic temperature requirements for the James Webb Space Telescope make it cost prohibitive to maintain a single optical metering structure. This paper demonstrates the advantages and challenges of separately isolating the test source from the telescope, while using the Johnson Space Center Vacuum Chamber A as the metering structure supporting the two isolated assemblies.