It’s Been Three Months in Deep Space, and Webb’s Mid-Infrared Instrument is Still Cooling Down

The James Webb Space Telescope is 1.5 million kilometers away from Earth. The temperature at which the telescope needs to operate is less than 40 K. One instrument needs to be even colder.

To operate at peak efficiency, the Mid-Infrared Instrument must be cooled to a chilly 7 K.

Most of the telescope and its instruments rely on the large sun shield and passive cooling of the JWST to take advantage of the frigid temperatures in deep space. The instruments have reached their target range by cooling.

To be able to detect the longer wavelength of the light, detectors need to be less than 7 K. This temperature is not possible by passive means alone, so Webb carries an innovative cryocooler that is dedicated to cooling the MIRI detectors so that they can see farther into theIR.

The entire telescope assembly was cooled by a freezing vapor produced by a tank of liquid liquid helium. The ability to cool the telescope was over once the supply of helium was gone. The mission ended in 2020.

The cooler reuses its own coolant just like the fridge in your kitchen.

Over the last couple weeks, the cryocooler has been circulating cold helium gas past the MIRI optical bench, which will help cool it to about 15 kelvins. The circulating helium gas will be forced through a flow restriction by operating the cryocooler. When the gas expands, it becomes cold and can bring the MIRI detectors to a cool operating temperature.

The lifetime of the MIRI instrument could be as long as 16 years if this type of recycling cooler is used. There is a possibility of a 20-year lifetime.

Engineers can begin the final phase of the telescope's construction once MIRI reaches the final temperatures.

Getting this instrument cold is one of the last major challenges faced by the team before they can relax. They said the cooler will pull out most of the heat from the metal and glass that was left in the launch site. The final instrument to open its eyes to the universe will be MIRI.

You can read more about how the cooler works. There is more information on the NASA website. The temperatures of all the instruments can be seen at the Where's Webb site.