Space Grant Consortium - University of Wisconsin - Green Bay

C. Structural Fortitude
Detector assemblies have been known to be sturdy structures. Previous designs
from Teledyne have had extensive thermal, structural, electrical, and optical modeling
analyses by Ball Aerospace. The SCA and flex cable have been shown to be resistant of
high cycle fatigue for 1000 thermal cycles. The thermal requirements for the SCA were
thought to be the most difficult for the component, yet it passed with a considerable
margin. The SCA is thought to be a robust component for spaceflight. The struts or
standoffs are also a stout part of the FPA. Their focus is to provide thermal isolation, but
they are very good in mechanical compliance between the molybdenum mosaic plate and
titanium baseplate. The struts are sized for optimum dynamic stiffness as well. [6][7]
D. Previous Shock Levels
A database of previous acceptance and qualification shock levels for FPAs would
have great use. This database would be a graph of collected SRS from past missions.
This could be used by projects like JWST to compare qualification levels of their project
to successful ones of the past. This comparison could lead to complete deferment of FPA
structures to shock testing or just a waiver to be used by one project. Either way, this
database will be a risk and cost saving tool in shock certification.
Results
Analysis of the detectors from several sources states that testing should be
deferred to the observatory level. The FPA structure is believed to be a strong design
with several components that support the idea that the design isn’t susceptible to shock.
Heritage of the structure shows that the design is not unique to JWST, even though the
ISIM’s infrared arrays have never been flown. Additionally, there have not been
documented shock failures of FPA structures. With the new Ariane fairing and LRM
devices lowering shock levels, previous projects infer that shock testing can be deferred.
A compilation of shock levels from previous missions will augment this mitigation study,
References
1. NASA GSFC. ISIM SI Shock Update 05/22. s.l. : JWST, 2009.
2. Hall, Donald N. B. HgCdTe Optical & Infrared Focal Plane Array Development in the Next Decade. s.l. :
Institute of Astronomy, University of Hawaii.
3. JPL MIRI FPS Team. Focal Plane System (FPS) Critical Design Review (CDR). JPL D-31387 DRD PM-20.
Pasadena, CA : NASA JPL, 2006.
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