NASA’s James Webb Space Telescope will see the first galaxies to form after the Big Bang, but to do so its instruments must first cool – very cold. On April 7, Webb’s average infrared instrument (MIRI) – a joint development of NASA and ESA (European Space Agency) – reached its final operating temperature below 7 Kelvin (minus 447 degrees Fahrenheit or minus 266 degrees Celsius). . Together with Webb’s other three instruments, MIRI initially cooled in the shadow of Webb’s tennis court-sized sunscreen, dropping to about 90 Kelvins (minus 298 F, or minus 183 C). But dropping to less than 7 Kelvin required an electric freezer. Last week, the team went through a particularly challenging milestone called the “pressure point” when the instrument goes from 15 Kelvin (minus 433 F, or minus 258 C) to 6.4 Kelvin (minus 448 F, or minus 267 C). . “The MIRI refrigerator team has put a lot of hard work into developing the traction process,” said Analyn Schneider, MIRI project manager at NASA’s Jet Propulsion Laboratory in Southern California. “The team was excited and nervous going into the critical activity. In the end it was a manual execution of the process and the cooler performance is even better than expected. “ The light beam coming from the telescope enters the MIRI through the mirror located at the top of the instrument and acts as a periscope. Then a series of mirrors redirect the light to the bottom of the instruments where a total of 4 spectroscopic units are located. Once there, the light beam is divided by optical elements called dichroism into 4 beams corresponding to different parts of the mid-infrared region. Each beam enters its own built-in field unit. These components separate and reshape the light from the entire field of view, ready to be dispersed in spectra. This requires light to fold, bounce, and split multiple times, making it probably one of Webb’s most complex light paths. To complete this amazing journey, the light of each beam is scattered through grids, creating spectra that are then projected onto 2 MIRI detectors (2 beams per detector). An amazing engineering achievement! Credit: ESA / ATG medialab Low temperatures are necessary because all four Webb instruments detect infrared light – wavelengths slightly longer than what the human eye can see. Distant galaxies, stars hidden in dust cocoons, and planets outside our solar system emit infrared light. But so do other hot objects, including Webb electronics and optics. Cooling of the four-instrument detectors and the surrounding material suppresses these infrared emissions. MIRI detects longer infrared wavelengths than the other three instruments, which means it must be even colder. Another reason Webb detectors need to be cold is to suppress something called dark current or electricity generated by the vibration of atoms in the detectors themselves. The dark current mimics a true signal to the detectors, giving the false impression that they have been struck by light from an external source. These false signals can drown out the real signals astronomers want to find. Since temperature is a measure of how fast people vibrate in the detector, lowering 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 must be colder than other instruments to completely eliminate this phenomenon. For each degree that the temperature of the instrument rises, the dark current increases by about 10. NASA tests Webb telescope MIRI thermal shield in a thermal vacuum chamber at NASA’s Goddard Space Flight Center in Greenbelt, MD. Credit: NASA Once MIRI reached the frozen 6.4 Kelvin, 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 data that describes the health of the organ and then gives the organ a set of instructions to see if it can perform the tasks properly. This milestone is the culmination of the work of scientists and engineers at many non-JPL institutions, including Northrop Grumman, who built the cryptocurrency, and NASA’s Goddard Space Flight Center, which oversaw the integration of MIRI and the refrigerator into the rest of the observatory. . . “We spent years practicing for that moment, passing the orders and tests we did at MIRI,” said Mike Ressler, a MIRI project scientist at JPL. “It was kind of like a movie script: Everything we had to do was written and we rehearsed. “When the test data was released, I was ecstatic to see that it looked exactly as expected and that we have a healthy organ.” There are even more challenges the team will have to face before MIRI can begin its scientific mission. Now that the instrument is at operating temperature, team members will capture test images of stars and other known objects that can be used to calibrate and control the instrument’s functions and functionality. The team will carry out these preparations in parallel with the calibration of the other three instruments, providing the first scientific images of the Webb this summer. “I’m very proud to be part of this highly motivated team of enthusiastic scientists and engineers from all over Europe and the United States,” said Alistair Glasse, MIRI Instrument Scientist at the UK Astronomy Technology Center (ATC) in Edinburgh, Scotland. This period is our “test with fire”, but it is already clear to me that the personal bonds and mutual respect we have created in recent years is what will make us in the coming months to offer a fantastic instrument to the world community. of astronomy “. More about shipping The James Webb Space Telescope is an international project 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 is leading the US MIRI effort, and a multinational consortium of European astronomical institutes is contributing to ESA. George Rieke of the University of Arizona is the head of the MIRI science team. Gillian Wright is MIRI’s lead researcher in Europe. Laszlo Tamas with the UK ATC manages the European Consortium. The MIRI freezer was developed under the leadership and management of JPL, in collaboration with Northrop Grumman in Redondo Beach, California, and NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
