ISIM - The Integrated Science Instrument Module on JWST
The ISIM is composed of three distinct areas:
The first area involves the cryogenic instrument module. This is a critical area because it cools the instrument components down to -234.15°C (39 K). The MIRI instrument is further cooled to -266.15°C (7 K) by a cryocooler refrigerator.
The second area is the ISIM Electronics Compartment, which provides the mounting surfaces and a thermally-controlled environment for the instrument control electronics.
The third area is the ISIM Command and Data Handling subsystem, which includes ISIM flight Software, and the MIRI cryocooler compressor and control electronics.