MIRI Imager

The imager module provides broad and narrow-band imaging (5-27 μm), coronagraphy, and low-resolution (R~100, 5-10 μm) slit spectroscopy using a single 1024x1024 pixels Raytheon Si:As sensor chip assembly (SCA) with 25 μm pixels.



As shown in the image above, MIRI consists of an optical bench assembly (OBA) with associated instrument control electronics (ICE), actively cooled focal-plane modules with associated focal plane electronics (FPE), and a Dewar with associated Dewar control electronics (DCE). The DCE interfaces with the spacecraft (S/C) command and telemetry processor (CTP), while the ICE and FPE interface with the ISIM C&DH. The OBA contains two actively cooled subcomponents, an imager, and an Integral Field Unit (IFU) spectrograph, plus an on-board calibration unit.

The image below the focal plane arrangement of the various elements of the MIRI imager. The region on the left is the clear aperture available for imaging. The gray region on the right marks the mechanical frame that supports the coronagraphic masks and the slit for the low-resolution spectrometer. The coronagraphic masks include three phase masks for a Quadrant phase coronagraph and one opaque spot for a Lyot coronagraph. The coronagraphic masks have a square field of view of 26″×26″ and are optimized for particular wavelengths (10.65, 11.5, 16 and 24 µm). The imager’s only moving part is an 18-position filter wheel. Filter positions are allocated as follows: 12 filters for imaging, 4 filter and diaphragm combinations for coronagraphy, 1 ZnS-Ge double prism for the low-resolution spectroscopic mode and 1 dark position. The imager will have a pixel scale of 0.11″ and a total field of view of 113″×113″; however, the field of view of its clear aperture is 84″×113″ because the coronagraph masks and the LRS are fixed on one side of the focal plane.

The MIRI imager's focal plane with sizes in pixels and mm.