This is a cross-grid detector element from an interim version of the X-ray imager intended for the Advanced X-ray Astrophysics Facility (AXAF), named Chandra after launch. The detector included a microchannel plate that collected the x-rays, converting them to electrons and amplified them by orders of magnitude. The signal was picked up by the cross grid detector and its strength and location was used to build an image of the source. The X-Ray Astronomy group at the Smithsonian Astrophysical Observatory designed and built this scaled-up version of the HRI on the way to building the imager that was installed on the final version of the AXAF which was named Chandra just before its launch. SAO transferred this detector to NASM in 2002.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.