National Aeronautics and Space Administration

And it fits perfectly (of course)! Here's the FEA integrated into the helium insert. You can see the silvery blocking filter (to let X-rays through but stop visible, ultraviolet, and infrared light) in the middle. Beside the filter are the two calibration source holders (only one of which is used). Further out are four of the twelve pairs of Kevlar strands which support the internal 60 millikelvin area from the warmer area outside. Around the outer part of the image is some of the plumbing and wiring for the insert.

FEA is Almost In Building the XRS Insert FEA in Place, With Lid