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.

Sub-picometer dynamic measurements of a diffuse surface.

Future space observatory missions are forecasting the need for sensing and controlling wavefront error and system alignment stability to picometer scale. Picometer stability performance demands precision knowledge of the mirror and metering structure materials to the same degree. A high-speed electronic speckle pattern interferometer was designed and built to demonstrate measurements of both static and dynamic responses of picometer amplitudes in materials of diffuse surface subjected to very low energy disturbances.

Measurement of picometer-scale mirror dynamics.

A high-speed interferometer has been designed and built to measure the dynamics of the James Webb Space Telescope primary mirror system currently under testing. This interferometer is capable of tracking large absolute motion (i.e.

Measurement of large cryogenic structures using a spatially phase-shifted digital speckle pattern interferometer.

The James Webb Space Telescope (JWST) Backplane Stability Test Article (BSTA) was developed to demonstrate large precision cryogenic structures' technology readiness for use in the JWST. The thermal stability of the BSTA was measured at cryogenic temperatures at the Marshall Space Flight Center (MSFC) X-Ray Calibration Facility (XRCF) and included nearly continuous measurements over a six-week period in the summer of 2006 covering the temperature range from ambient down to 30 Kusing a spatially phase-shifted digital speckle pattern interferometer (SPS-DSPI). The BSTA is a full size, one-sixth section of the JWST primary mirror backplane assembly (PMBA).

Calibration of spatially phase-shifted DSPI for measurement of large structures.

We present a method for the calibration of a spatially phase-shifted digital speckle pattern interferometer (SPS-DSPI), which was designed and built for the purpose of testing the James Webb space telescope (JWST) optical structures and related technology development structures. The need to measure dynamic deformations of large, diffuse structures to nanometer accuracy at cryogenic temperature is paramount in the characterization of a large diameter space and terrestrial based telescopes. The techniques described herein apply to any situation, in which high accuracy measurement of diffuse structures are required.