Out-of plane deformation measurements
of the 3 m diameter Backplane
Stability Test Article (BSTA) for the
James Webb Space Telescope, obtained
by a spatially phase-shifted digital speckle-pattern interferometer.
The "snapshots" are taken with temperature
intervals of 2 K during a 40 K
to 60 K test. The dark red indicates
1.8 μm deformation toward the observer; the dark blue indicates
3.0 μm deformation away from the
observer. The mirror segment assembly
fittings (squares) bend away from
the observer due to the negative coefficient thermal expansion of lnvar.
The frame tubes bulge forward because
of their "hour-glassing" behavior
as a function of temperature.
For further details, see the paper by
Saif et al. pp. 737-745.