/// THERMAL ENGINEERING \\\


Temperature plunges for space instrument


The MIRI instrument on the Webb telescope has been reduced to its final operating temperature in space


cooled down to its operational temperature. MIRI was the last instrument on the tele-


T


scope to reach the temperature required for scientific operations, marking an incredibly important stage in the mission’s progress to- wards full science mode.


The coldest instrument on Webb \\\ The James Webb Space Telescope, known sim-


ply as Webb, is the largest, most powerful tele- scope ever launched into space and MIRI is one of four scientific instruments on board. MIRI was last to reach this important mile-


stone as it operates at 7K (-266C), a colder temperature than the other instruments. To achieve this, MIRI needed to be cooled


by a cryogenic refrigerator, or cryocooler. The cryocooler was specially developed by NASA’s Jet Propulsion Laboratory while the Science and Technology Facilities Council’s (STFC) RAL Space in the UK were responsible for overall instrument thermal engineering. If too much heat is transferred to the


cooler, MIRI cannot reach temperature. There- fore, a key role for RAL Space’s thermal engi- neers was to develop a design that minimised this heat transfer. This is because the instru- ment sees in mid-infrared light and every ob- ject emits infrared radiation, or heat, all the time. So MIRI must be cold to ensure its de- tectors do not pick up any background heat from the instrument itself, obscuring what the astronomers actually want to see. Dr Bryan Shaughnessy, leader of RAL


Space’s Thermal Engineering Group, said: “I have been involved in the thermal design, analysis and testing for MIRI for almost 20 years so to finally see the instrument reach- ing 7K in space and well on its way to science operations is incredibly exciting. Our team has worked hard to make sure everything works at this challenging temperature and the last few months monitoring the cool down has been the culmination of all of our


The MIRI Structural Thermal Model underwent intensive testing


efforts. I’m looking forward to seeing the first results at the end of the commissioning pro- cess.”


The mission so far \\\ After successfully launching on Christmas Day


2021, Webb spent a month travelling through space to reach its new home in orbit 1 million miles from Earth. Over the past two months the commissioning team has been working on aligning the 18 mirror segments and cooling down the scientific instruments. Scientists, engineers and astronomers from


STFC’s UK ATC and RAL Space are actively in- volved in this complex and painstaking com- missioning process. Working alongside international colleagues at the Space Tele- scope Science Institute in Baltimore, the team is monitoring and commanding MIRI and Webb in shifts, 24 hours a day. This work follows years of testing, prepara- tion and rehearsal by the UK team both be- fore and after the instrument was delivered to NASA in 2012. While still at RAL Space in Ox- fordshire, MIRI underwent 100 days in a ther- mal vacuum chamber where it spent 85 days


below room temperature to make sure all the components would work correctly at the low temperatures needed. Further cryogenic test- ing was then carried out with the other Webb instruments at NASA’s Goddard Space Flight Center and the integrated telescope and in- struments were thoroughly tested at John- son Space Center. Professor Gillian Wright, European principal


investigator for MIRI and director of UK ATC, said: “It is fantastic to know that the instru- ment has successfully reached operating temperature. The MIRI cryocooler is a real technical first, and it is a great testament to the talents of our JPL partners, who led the cryocooler development, that the cool-down process has worked as anticipated. As the last instrument to reach operational temperature, this a significant milestone in MIRI and Webb’s lifetime.” Once MIRI had successfully cooled down,


the commissioning process continued for a number of months during which MIRI’s sys- tems were tested and final adjustments made before the first spectacular images of the cos- mos could be revealed. C&VT


2022 /// Climatic & Vibration Testing \\\ 3


he UK’s main contribution to the James Webb Space Telescope, the Mid-Infrared Instrument (MIRI), has been carefully


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