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Space Grant Consortium - University of Wisconsin - Green Bay

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B. FPA Material Comparison<br />

The FPAs <strong>of</strong> JWST all share the same core components. Each FPA, however, is<br />

its own version <strong>of</strong> the shared design. These versions utilize different materials for some<br />

components. The ROIC for all the FPAs is made <strong>of</strong> silicon because it is an integrated<br />

circuit similar to one used for a computer chip. The SCA mount is made <strong>of</strong> a TMZ<br />

Molybdenum hybrid for all the instruments, except MIRI which uses a copper alloy.<br />

These were chosen because they provide good coefficient <strong>of</strong> thermal expansion (CTE)<br />

match with the ROIC. The interface plate between the SCA mount and mosaic plate is<br />

also made <strong>of</strong> Molybdenum for similar purposes. The three flexure struts, which also<br />

serve as stand<strong>of</strong>fs, that connect the mosaic plate to the baseplate are made <strong>of</strong> Titanium.<br />

The struts accommodate thermal mismatches and provide active temperature control.<br />

The baseplate is made <strong>of</strong> Titanium, Molybdenum for MIRI, and provides a strong base<br />

for the assembly. The assembly housing for radiation shielding and shadow mask stray<br />

light mitigation are unique to each FPA. [3][11]<br />

NIRSpec FPA NIRCam FPA<br />

MIRI FPA FGS FPA [16][17][8][4]<br />

63

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