NASA’s James Webb Space Telescope would see the first galaxies form after the big bang, but to do that, its instruments would first need to cool down – really cold. On April 7, Webb’s Mid-Range Infrared Instrument (MIRI) – a co-development of NASA and ESA (European Space Agency) – reached a final operating temperature of less than 7 kelvins ( minus 447 degrees Fahrenheit or minus 266 degrees Celsius).
Along with three other Webb devices, the MIRI was initially cooled in the shade of Webb’s tennis court-sized sunshade, dropping to about 90 kelvins (minus 298 F, or minus 183 C). But falls below the required 7 kelvins electric chiller. Last week, the team passed a particularly difficult milestone called “pinch pointWhen the device goes from 15 kelvins (minus 433 F or minus 258 C) to 6.4 kelvins (minus 448 F or minus 267 C).
“The MIRI cooling team spent a lot of work developing the process for the pinch point,” said Analyn Schneider, MIRI project manager at NASA’s Jet Propulsion Laboratory in Southern California. “The whole team is both excited and nervous about entering the important activity. In the end, it’s a textbook execution, and cooler performance is even better than expected. “
Low temperature is necessary because all four tools of Webb detect Infrared lights – The wavelength is slightly longer than the wavelength that can be seen by the human eye. Distant galaxies, stars hidden in dust cocoons, and planets outside our solar system all emit infrared light. But so are other warm objects, including Webb’s optical and electronic hardware. Cooling the transducers of the four devices and surrounding hardware will suppress those infrared emissions. MIRI detects infrared wavelengths longer than the other three, which means it need to be colder.
Another reason Webb’s detector needs to be cold is to suppress something called dark currents, or currents created by the vibrations of atoms within the detector itself. Dark currents mimic the real signals in the detector, giving the false impression that they are hit by light from an external source. Those false signals can drown out the real signals that astronomers want to find. Since temperature is a measurement of how fast the atoms in the detector vibrate, a decrease in 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 currents, so it needs to be cooler than other devices to completely cancel out that effect. For each degree the device’s temperature increases, the dark current will increase by about 10.
Once the MIRI hit 6.4 kelvins, scientists began a series of tests to make sure the detectors were working as expected. Like a doctor looking for any sign of illness, the MIRI team looks at the device’s health-describing data, then feeds the device a series of commands to see if it can perform tasks. correct or not. This milestone is the culmination of the work of scientists and engineers at numerous organizations outside of JPL, including Northrop Grumman, the company that built the chiller, and NASA’s Goddard Space Flight Center, which oversees Observe the integration of the MIRI and cooler with the rest of the observatory .
“We spent years practicing for that moment, running through the commands and tests we performed on MIRI,” said Mike Ressler, MIRI project scientist at JPL. “It was like a screenplay: Everything we had to do was written down and rehearsed. When the test data came in, I was happy to see that it looked exactly as expected and that we had a healthy tool.”
There are still many challenges the team will face before MIRI can begin its scientific mission. Now that the instrument is at operating temperature, team members will take test images of the stars and other known objects that can be used to calibrate and test the operations and functions of the device. device. The team will carry out these preparatory works, along with calibrating the remaining three instruments, providing Webb’s first scientific images this summer.
Alistair Glasse, MIRI instrument scientist at the UK Astronomical Technology Center (ATC) in Edinburgh, Scotland said: “I am incredibly proud to be part of a dynamic group of scientists and engineers, Enthusiasm came from all over Europe and the United States. “This period has been our ‘test of fire’ but it has become clear to me that the personal relationship and mutual respect we have built over the years is what will get us through. over the next few months to provide an amazing tool for the worldwide astronomy community. ”
More information about the mission
The James Webb Space Telescope is an international program led by NASA with its partners, ESA and Canadian space agency.
MIRI was developed through a 50-50 partnership between NASA and ESA. JPL leads US efforts for MIRI, and a multinational consortium of European astronomical institutes contributes to ESA. George Rieke with the University of Arizona as MIRI science team leader. Gillian Wright is the principal investigator for MIRI Europe.
Laszlo Tamas with the UK’s ATC manages the European Association. The MIRI chiller development is 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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