The ISIM structure at the GSFC during testing in 2009. Credit: NASA	Schematic diagram of the four science instruments integrated in the ISIM structure. Credit: NASA

The ISIM is composed of three distinct areas:

The first area involves the cryogenic instrument module. This is a critical area, because it keeps the instrument components cool, down to 39 Kelvin. The MIRI instrument is further cooled - to 7 Kelvin - 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.