On-orbit Thermal Performance of the JWST Mid-Infrared Instrument

The James Webb Space Telescope (JWST) observatory was launched on the 25th December 2021. This was followed by a commissioning phase of about six months, where the observatory deployed to its final configuration and transferred to its L2 orbit location, whilst cooling science components and instruments down to their cryogenic operating temperatures. The Mid-Infrared Instrument (MIRI) is one of four scientific instruments on the JWST observatory. It provides unique capabilities to probe the deeply dust-enshrouded regions of the universe, investigating the history of star formation both near and far. The MIRI is the coldest instrument on the observatory. Its thermal design is driven by requirements to cool an Optics Module (OM) to below 16 K and detectors within this to below 7 K with a stability of <10 mK over 1000 seconds. The OM is accommodated within the passively cooled Integrated Science Instrument Module (ISIM). The instrument temperatures are achieved by a combination of thermal isolation from the ISIM and active cooling by a dedicated cryocooler. This paper summarises briefly the thermal design and pre-launch thermal verification of the instrument. It goes on to report the MIRI thermal performance through the commissioning phase, and concludes with lessons that can be applied to future similar missions.