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.

Date Published: 23 October 2007
PDF: 10 pages
Proc. SPIE 6675, Optical Modeling and Performance Predictions III, 667504 (23 October 2007); doi: 10.1117/12.745947

Published in SPIE Proceedings Vol. 6675:
Optical Modeling and Performance Predictions III
Mark A. Kahan, Editor(s)