Tracking sub-nanometer thermal structural changes with speckle interferometry

Based on our results of the James Webb Space Telescope (JWST) center-of-curvature tests where we were able to measure dynamic amplitudes of Zernike terms to the order of a few picometers, we have applied the same approach to determine if it is possible to measure the accuracy of higher-order Zernike terms as a function of time rather than frequency, i.e., static measurements in place of measuring the amplitude of frequency components. We have applied this approach to data taken for the JWST backplane structure test article (BSTA) in 2006 and find that we can measure effects at the sub-nanometer level, as small as 50 pm for Zernike terms over 30. We conclude that these results show it will be possible to use these techniques to ensure that the optics and support structure for large space telescopes can meet the necessary stability requirements for detecting spectral signatures of life on Earth-like extra-solar planets.