The aperture cylinder on the top of the Dewar. This is where the X-rays enter the Dewar. You can see the CTS filter (an X-ray filter attached to the Calorimeter Thermal Sink) at the bottom of the cylinder (the detectors are just under it), and the bolt circles for the four other filters. The filters furthest from the detectors (closest to you) are largest.

XRS Flight Dewar With Lid Flight Dewar and detectors Installing the last filter

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