Webb Telescope’s Coldest Instrument Reaches Operating Temperature


In this illustration, the multilayered sunshield on NASA’s James Webb Space Telescope stretches out beneath the observatory’s honeycomb mirror. The sunshield is the first step in cooling down Webb’s infrared instruments, but the Mid-Infrared Instrument (MIRI) requires additional help to reach its operating temperature. Credits: NASA GSFC/CIL/Adriana Manrique Gutierrez

NASA’s James Webb Space Telescope will see the first galaxies to form after the big bang, but to do that its instruments first need to get cold – really cold. On April 7, Webb’s Mid-Infrared Instrument (MIRI) – a joint development by NASA and ESA (European Space Agency) – reached its final operating temperature below 7 kelvins (minus 447 degrees Fahrenheit, or minus 266 degrees Celsius).

Along with Webb’s three other instruments, MIRI initially cooled off in the shade of Webb’s tennis-court-size sunshield, dropping to about 90 kelvins (minus 298 F, or minus 183 C). But dropping to less than 7 kelvins required an electrically powered cryocooler. Last week, the team passed a particularly challenging milestone called the “pinch point,” when the instrument goes from 15 kelvins (minus 433 F, or minus 258 C) to 6.4 kelvins (minus 448 F, or minus 267 C).

“The MIRI cooler team has poured a lot of hard work into developing the procedure for the pinch point,” said Analyn Schneider, project manager for MIRI at NASA’s Jet Propulsion Laboratory in Southern California. “The team was both excited and nervous going into the critical activity. In the end it was a textbook execution of the procedure, and the cooler performance is even better than expected.”

The low temperature is necessary because all four of Webb’s instruments detect infrared light – wavelengths slightly longer than those that human eyes can see. Distant galaxies, stars hidden in cocoons of dust, and planets outside our solar system all emit infrared light. But so do other warm objects, including Webb’s own electronics and optics hardware. Cooling down the four instruments’ detectors and the surrounding hardware suppresses those infrared emissions. MIRI detects longer infrared wavelengths than the other three instruments, which means it needs to be even colder

Another reason Webb’s detectors need to be cold is to suppress something called dark current, or electric current created by the vibration of atoms in the detectors themselves. Dark current mimics a true signal in the detectors, giving the false impression that they have been hit by light from an external source. Those false signals can drown out the real signals astronomers want to find. Since temperature is a measurement of how fast the atoms in the detector are vibrating, reducing the temperature means less vibration, which in turn means less dark current.

MIRI’s ability to detect longer infrared wavelengths also makes it more sensitive to dark current, so it needs to be colder than the other instruments to fully remove that effect. For every degree the instrument temperature goes up, the dark current goes up by a factor of about 10.

Once MIRI reached a frigid 6.4 kelvins, scientists began a series of checks to make sure the detectors were operating as expected. Like a doctor searching for any sign of illness, the MIRI team looks at data describing the instrument’s health, then gives the instrument a series of commands to see if it can execute tasks correctly. This milestone is the culmination of work by scientists and engineers at multiple institutions in addition to JPL, including Northrop Grumman, which built the cryocooler, and NASA’s Goddard Space Flight Center, which oversaw the integration of MIRI and the cooler to the rest of the observatory.

“We spent years practicing for that moment, running through the commands and the checks that we did on MIRI,” said Mike Ressler, project scientist for MIRI at JPL. “It was kind of like a movie script: Everything we were supposed to do was written down and rehearsed. When the test data rolled in, I was ecstatic to see it looked exactly as expected and that we have a healthy instrument.”

There are still more challenges that the team will have to face before MIRI can start its scientific mission. Now that the instrument is at operating temperature, team members will take test images of stars and other known objects that can be used for calibration and to check the instrument’s operations and functionality. The team will conduct these preparations alongside calibration of the other three instruments, delivering Webb’s first science images this summer.

“I am immensely proud to be part of this group of highly motivated, enthusiastic scientists and engineers drawn from across Europe and the U.S.,” said Alistair Glasse, MIRI instrument scientist at the UK Astronomy Technology Centre (ATC) in Edinburgh, Scotland. “This period is our ‘trial by fire’ but it is already clear to me that the personal bonds and mutual respect that we have built up over the past years is what will get us through the next few months to deliver a fantastic instrument to the worldwide astronomy community.”  

More About the Mission

The James Webb Space Telescope is an international program led by NASA with its partners, ESA and the Canadian Space Agency.

MIRI was developed through a 50-50 partnership between NASA and ESA. JPL leads the U.S. efforts for MIRI, and a multinational consortium of European astronomical institutes contributes for ESA. George Rieke with the University of Arizona is the MIRI science team lead. Gillian Wright is the MIRI European principal investigator.

Laszlo Tamas with UK ATC manages the European Consortium. The MIRI cryocooler development was led and managed by JPL, in collaboration with Northrop Grumman in Redondo Beach, California, and NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

For more information about the Webb mission, visit:


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Robert Heath
April 14, 2022 2:28 am

Just imagine if climate science were conducted properly too.

Flash Chemtrail
Reply to  Robert Heath
April 14, 2022 6:19 am

Just imagine if NASA stopped wasting money on manned space flight and instead concentrated on real science.

Reply to  Flash Chemtrail
April 14, 2022 7:23 pm

Manned? When was the last time NASA was able to safely put a man in low orbit?

Reply to  Flash Chemtrail
April 15, 2022 9:45 am

Flash, time to get up to speed. How many astronauts fly on JWST?
…um, this is real science, but then again how might you know?.

Andy Espersen
Reply to  Robert Heath
April 14, 2022 10:43 am

That exactly was also my thought while reading this immensely interesting article! How to do it?? Leave it all to real climate scientists to examine.

One does not become a “climate scientist” merely by claiming to be one – or (as a 12-year old schoolgirl!) piping up about climate change – or by being referred to as one by journalists – or by being appointed by politicians to the board of IPCC. Generally speaking, climatologists have academic degrees in studies such as meteorology, chemistry, atmospheric physics, mathematics (computer modelling), oceanography, etc. The scientific discipline closest to climate science is paleo-climatology – a subbranch of geology. Paleo-climatologists study climate changes in the past – over the time of 4 billion years.

Pay, say 12, of the world’s top climatologists extremely well to write a thorough report on the question of anthropogenic climate change – including their balanced opinion on how urgent and serious a threat it presents to our civilised world.

Gordon A. Dressler
Reply to  Andy Espersen
April 16, 2022 8:57 am

“Pay, say 12, of the world’s top climatologists extremely well to write a thorough report on the question of anthropogenic climate change – including their balanced opinion on how urgent and serious a threat it presents to our civilised world.”

And at the end, what difference would it make?

What? . . . you think the IPCC and climate “scientists” will change their alarmism (and thus go out of business) based on a single report from a mere 12 scientists, no matter their credentials?

Also, I can predict with “high confidence”, using the IPCC’s own terminology, that any such report from 12 co-authors will conclude that the effect(s) anthropogenic emissions into the atmosphere have on global temperatures and other climate-related metrics (i.e., mankind’s total effect on climate change™) is uncertain, and therefore more funding is needed to study the issue in greater detail.

April 14, 2022 2:41 am

As cold as Mann!

I look forward to the wonders yet to be revealed, but they seem to be on to Webb’s successor already…

“Liquid lenses could make NASA’s next space telescope even more powerful than Webb”.

“telescopes ten—or even 100—times larger than the James Webb Space Telescope (JWST)”

NASA’s next massive telescope could have a liquid lens | Popular Science (popsci.com)

Last edited 1 month ago by fretslider
Rud Istvan
Reply to  fretslider
April 14, 2022 3:23 pm

Hard to keep liquids liquid at the temperatures of outer space.

Reply to  Rud Istvan
April 14, 2022 10:18 pm

formed while liquid, then hardened into their permanent shape.

Ron Long
April 14, 2022 3:24 am

Glad to hear the James Webb Space Telescope has reached operating temperature. I reach my operating temperature half-way through the first cup of coffee. This technical marvel (the telescope, not me) should provide some excellent data, and should be model for government conduct of scientific research.

Reply to  Ron Long
April 14, 2022 4:24 am

“and should be model for government conduct of scientific research.”

Please., no more models !! 😉

Michael S. Kelly
Reply to  Ron Long
April 14, 2022 8:29 pm

I’m very proud of the fact that my wife ran the Northrop-Grumman (NGC) cryocooler qualification tests for JWST. Much later, I became a DARPA program manager, and brought in some NGC people to pitch their cryocooler technology. I think the most important part of that technology is running it in reverse, to generate power over a temperature difference. It is way, way more efficient than solar photovoltaic.

Reply to  Michael S. Kelly
April 14, 2022 10:22 pm

a better thermocouple?

Reply to  Michael S. Kelly
April 15, 2022 6:05 pm

Michael, I very well may have crossed paths with your wife, as I spent a great deal of time in those spheres testing systems on JWST. As I recall it would take quite some time to even get down to those temps.

Reply to  Ron Long
April 14, 2022 8:50 pm

Keep governments out of scientific research.

April 14, 2022 3:39 am

And let’s look forward to the CERN Large Hadron Collider coming back fully online after its maintenance and upgrades are complete.

If anybody follows their work on atmospheric aerosols and can write an article for WUWT, there is one reader here who would be grateful. CERN have a whole department dedicated to the study.
Aerosol action in the life of clouds is not often talked about. As clouds are the largest greenhouse gas that none of the alarmists talk about, it would be a welcome contribution on WUWT as far as I’m concerned…_


Last edited 1 month ago by DiggerUK
Peta of Newark
April 14, 2022 3:48 am

At least somebody inside NASA has their head around the 2nd Law

(We all do realise how the operation of this thing rides a Coach & Horses through every explanation of the Green House Gas Effect)

Wouldn’t a 3 cylinder radial compressor have been lower vibration than a boxer twin? Or as the have 2 of them, a 6-pot radial would be a sweet as little nut.
haha ‘nut’
Ideal for attracting squirrels.

Ed Bo
Reply to  Peta of Newark
April 14, 2022 12:41 pm

Peta – The Webb spent months inside a giant vacuum chamber for tests of its future performance in space. The walls of the chamber were covered by super-cooled “shrouds” to bring the surface temperature down to about 20K. This was done at incredible expense.

Why did they do that? It was to eliminate the “back radiation” from the chamber surface, which would be about 400 W/m2 at normal temperatures. It is a great confirmation of the basic idea of the so-called greenhouse effect.

April 14, 2022 5:38 am

The engineering behind cooling things in space (vacuum) is pretty fascinating since you basically have to rely only on thermal radiation. The ISS uses external thermal radiators pointed to empty space for example. For the Webb, the average temperature of space is 3K, so the closer you get to it the longer it takes to get there. Kudos to the designers on coming up with a robust way to do it.

Reply to  rbabcock
April 14, 2022 6:36 pm

Apparently NASA used a helium gas refrigerator to get the instrument below 90K.

Reply to  rbabcock
April 15, 2022 6:12 pm

The cooling system you refer to was called the DSIR (Deep Space IR Radiator) array. It was a deployed system separated from the main mast and angled for radiative purposes so as not to be effected by JWST itself. It took several weeks of special design test equipment to cool the vacuum sphere chambers to test out the systems.

April 14, 2022 6:17 am

I wonder what the coldest object/place in the solar system is.

Reply to  ResourceGuy
April 14, 2022 6:58 am

Probably somewhere in the outskirts of the Oort cloud?

Gordon A. Dressler
Reply to  ResourceGuy
April 14, 2022 8:06 am

Some people have argued, with reason, that it would be on the shores of Chicago during the depth of winter when a stiff wind is blowing.

Reply to  ResourceGuy
April 14, 2022 1:50 pm

The coldest known temp was right here on earth…they use lasers to slow molecular motion of atoms…they are achieving temps well below 1 degree K and it is a very interesting area of physics….the Uncertainty Principle…..quantum mechanics…Bose-Einstein condensate…quantum computers….it has it all

Gordon A. Dressler
Reply to  Anti-griff
April 14, 2022 3:12 pm

. . . and none of which is practical in the “real world” (in the absence of active cryogenic cooling) where ambient temperatures are usually* above -80 °C (+193 K).

*Coldest temperature ever recorded at the South Pole is -82.8 °C,

Reply to  ResourceGuy
April 14, 2022 6:40 pm

Putin’s heart would be pretty hard to beat…

Nicholas McGinley
Reply to  ResourceGuy
April 15, 2022 7:55 am

Once upon a time, sci fi author Larry Niven wrote a short story called “The Coldest Place”, about the coldest place in the solar system.
In the story, an astronaut who wound up in this place had some sort of mishap which caused his life support to fail in his space suit, so he was flash cooled to cryogenic temperatures.
Unfortunately for him, this caused his nervous system to become a superconductor, and he was stuck frozen in place both with his consciousness fully intact, with no hope of being found or escaping…forever.
In the story, this place was inside a crater at one of the poles of the planet Mercury, which at the time it was thought to be tidally locked as the Moon is to Earth, so the bottom of the crater saw only the endless dark and cold of space.

Last edited 1 month ago by Nicholas McGinley
Ric Werme(@ricwerme)
Reply to  Nicholas McGinley
April 16, 2022 11:48 am

Niven wrote a later story, Wait it Out, set at Pluto. I don’t see it online, but a very good synopsis is at https://scifi.stackexchange.com/questions/200030/sci-fi-short-story-about-stranded-pilots-on-frozen-planet

and are finally both frozen semi-solid

Stars rolling up the sky. The same patterns, endlessly rolling up from the same points. Does Jerome’s corpse live the same half-life I live now? He should have stripped, as I did.

My God! I wish I’d thought to wipe the ice from his eyes! I wish that superfluid blob would come back.

Damn. It’s cold.

Last edited 1 month ago by Ric Werme
Gordon A. Dressler
April 14, 2022 8:02 am

Unfortunately, left unmentioned in the above article is the fact that the “universal” cosmic background radiation is equivalent to a (more or less) uniform space “temperature” of 2.7 K.

This means that MIRI is operating at only 3.7 K temperature difference (aka, delta-T) above the background “temperature” of space itself.

Simply amazing technology!

Last edited 1 month ago by Gordon A. Dressler
Rud Istvan
April 14, 2022 3:30 pm

For those interested, go to NASA’s description and pictures of the Webb MIRI cryocooler. An incredibly impressive and complex ‘refrigerator’. The main problem was insuring NO vibration. They did that basically using the old horizontal opposed BMW motorcycle engine trick with an unbelievable amount of precision.

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