ISIM meaning in Governmental ?

Integrated Science Instrument Module (ISIM) is a component of the James Webb Space Telescope, a large international infrared space telescope planned for launch in December 2021. ISIM is the heart of the JWST, and holds the main science payload which includes four science instruments and the fine guidance sensor.

ISIM is the spacecraft chassis and instruments that take the light from the main mirror and convert that into the science data that is then sent back to Earth. The other two major sections of the JWST are the Optical Telescope Element (OTE) (mirror and their structure) and the Spacecraft Element (SE), which includes the Spacecraft Bus and Sunshield. ISIM has a mass of 1400 kg (3086 lb), about 23% of the mass of the JWST.

The infrared camera instrument integrated with ISIM passed its thermal tests in early 2016. ISIM underwent intense thermal cold testing in late 2015 to early 2016. NIRcam is extremely important to JWST, because it's not only a sensitive infrared camera, but it is also used to adjust the alignment of the main mirror segments. The tests were very positive because NIRcam showed was very stable through vibration and thermal testing. NIRcam was installed into ISIM in March 2014, and then underwent integration and testing after that, as the telescope is readied for its 2019 launch.