Integrated modeling activities for the James Webb Space Telescope: structural-thermal-optical analysis

Abstract

The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 20 1 1. This is a continuation of a series of papers on modeling activities for JWST. The structural-thermal-optical, often referred to as "STOP, analysis process is used to predict the effect of thermal distortion on optical performance. The benchmark STOP analysis for JWST assesses the effect of an observatory slew on wavefront error. Temperatures predicted using geometric and thermal math models are mapped to a structural finite element model in order to predict thermally induced deformations. Motions and deformations at optical surfaces are then input to optical models. and optical performance is predicted using either an optical ray trace or a linear optical analysis tool. In addition to baseline performance predictions, a process for performing sensitivity studies to assess modeling uncertainties is described.

MTF Analysis for the Image Performance Prediction of Observation Satellites

“…5 is used to predict the influence of optical performance by the thermal variation. [4] In the thermal model the temperature variation at electro-optical imaging system on on-orbit conditions is predicted, and the structural model calculates deformations by the mapping of temperatures to structure. Then the optical model computes wave-front errors by thermal deformation through ray-trace analysis.…”

“…A schematic of integrated performance analysis of an observation satellite is shown in Fig. 1 Research on integrated analysis of an observation satellite has been performed on space telescope observatories such as Next Generation Space Telescope (NGST), James Webb Space Telescope (JWST), Jupiter Magnetospheric Explorer (JMEX), and Terrestrial Planet Finder (TPF), and are categorized into StructuralThermal-Optical Performance (STOP) analysis of thermal stability of the satellite and jitter stability analysis of estimating blurs and distortion of images due to uncompensated alignment and vibration [1][2][3][4][5][6]. This paper confirms a falling-off in image performance by the thermal deformation and jitter in space environment on a basis of these integrated analyses.…”

Improving active space telescope wavefront control using predictive thermal modeling

“…These coefficients, along with the remaining thermal model parameters such as the temperature range, are loosely derived from the results of detailed finiteelement thermal modeling of the temperature evolution following a worst-case cold-to-hot slew. 19 Fig. 1 Sample temperature and wavefront evolution for a repeated slew between two attitudes.…”

“…As an example, distortions of the primary mirror backplane support structure are expected to dominate the WFE evolution for JWST, and these distortions correspond to changes in the average backplane temperature. 17,19 The model also assumes that the thermal changes are caused only by variations in the spacecraft orientation with respect to the sun (hereafter "sun angle"). Although changes due to roll or other sources could be included in a more sophisticated model, these perturbations are small by comparison.…”

“…The cosinusoidal variation is presented as a conceptual example of how the temperature might depend on the sun angle, but we have selected a more general quadratic model since there are likely additional effects that influence the specific temperature dependency.) In the case of JWST, detailed finite element modeling 19 has concentrated on the hottest and coldest attitudes, so we fit a, b, and c by considering these extreme cases. These attitudes determine the temperature range, and they are affected by the sunshield geometry and the pointing restrictions.…”