Space Grant Consortium - University of Wisconsin - Green Bay

B. Microshutter History of Risk in Testing
The Microshutters are a brand new technology that was created for the NIRSpec
instrument on the JWST. This technology provides the most precise in space
spectroscopy to date. The Microshutters are an array of individual micron scale cells
with lids that open and close with a magnetic field in order to survey the spectra of 100
objects at a time as well as block out the other portions in space.
The Microshutter Assembly (MSA) is the enclosure for the array that must be
flight certified for shock. The Microshutters are new technology with no flight heritage
and because of this it was determined that the MSA be tested for shock certification.
Similar to the FPAs, the MSA is on the Science Instrument (SI) level of the ISIM. The
MSA was shocked to the SI specification. The Microshutters failed their initial testing as
the array was severely fractured. This failure had several costly repercussions. Broken
hardware, the need for more testing and a delay in the project schedule were the results.
It was confirmed that the testing did not simulate the shock that the MSA will really
encounter. The predicted levels of the shock that were given for the MSA were much
higher than they should have been. Since the initial failure of the MSA, more precise and
expensive tests were done at facilities in Europe and the U.S. until the MSA could finally
be qualified for shock. The entire ordeal of qualifying the MSA demonstrates the risks of
direct testing of shock for structures at the SI level.
The Microshutter Assembly (MSA) Individual microscopic shutters
C. Testing deferral to Observatory level
From previous examples, there is a definite risk for shock testing at the SI level.
To avoid this, testing can be deferred to the next larger level. The observatory level is the
next level for shock testing the FPAs and the decision to defer shock testing for FPAs is
based on an assessment of the strength and robustness of the assembly. Dominant
assembly resonance is one area of consideration for the sturdiness of a structure. A Jet
Propulsion Laboratory (JPL), analysis of the predicted shock on the FPMs for MIRI
(Focal Plane Module and Focal Plane Assembly are synonyms), from the MIRI
Requirements Document (JWST-IRD-000782 Revision K), showed that the response of
the FPM and the internal detector assembly, were not sensitive to the shock levels given
from the Observatory Base requirements Document (JWST OBA RD). As a result, JPL
concluded that a SI level shock test of the FPM was not necessary and that shock testing
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