A document describes cryogenic test architecture for the James Webb Space Telescope (JWST) integrated science instrument module (ISIM). The ISIM element primarily consists of a mechanical metering structure, three science instruments, and a fine guidance sensor. One of the critical optomechanical alignments is the co-registration of the optical telescope element (OTE) exit pupil with the entrance pupils of the ISIM instruments. The test architecture has been developed to verify that the ISIM element will be properly aligned with the nominal OTE exit pupil when the two elements come together.
The architecture measures three of
the most critical pupil degrees-of-freedom
during optical testing of the ISIM
element. The pupil measurement
scheme makes use of specularly reflective
pupil alignment references located
inside the JWST instruments, ground
support equipment that contains a pupil
imaging module, an OTE simulator, and
pupil viewing channels in two of the
JWST flight instruments.
Pupil alignment references (PARs)
are introduced into the instrument, and
their reflections are checked using the
instrument’s mirrors. After the pupil
imaging module (PIM) captures a
reflected PAR image, the image will be
analyzed to determine the relative alignment
offset. The instrument pupil alignment
preferences are specularly reflective
mirrors with non-reflective fiducials,
which makes the test architecture feasible.
The instrument channels have fairly
large fields of view, allowing PAR tip/tilt
tolerances on the order of 0.5°.
This work was done by Brent Bos, David A. Kubalak, Scott Antonille, Raymond Ohl, and John G. Hagopian of Goddard Space Flight Center. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Physical Sciences category. GSC-15650-1