Two weeks after being launched from the Kourou spaceport in French Guiana, the James Webb Space Telescope has entered a ‘period of cooldown’ after being completely unfolded in space. The final leg of risky deployments ended on January 8 when the engineers handling the telescope successfully unfurled Webb’s tennis court-sized sun shields and exposed its mirrors in a week-long process. NASA says that now that the multi-billion dollar observatory has crossed the most complex part of the mission, its instruments will now be cooled down to temperatures below -200° celsius.
What happens in the ‘period of cooldown’?
As per NASA’s description, the telescope is still way off from its operating temperature, which needs to be about -233° celsius for Webb to detect infrared light. According to the agency’s live Webb tracker, the temperature on the telescope’s side facing away from the sun is only around -184° C and needs to be further cooled down before the telescope begins its observations. The Webb telescope has two sides, one which faces the sun and carries instruments like a solar panel, communications antenna, and a computer whereas the other side, which is also the colder one, carries the golden mirrors and four scientific instruments.
Among Webb’s instruments is the Near-Infrared Camera (NIRCam), Near-Infrared Spectrograph (NIRSpec), Mid-Infrared Instrument (MIRI), and Fine Guidance Sensor/ Near InfraRed Imager and Slitless Spectrograph (FGS/NIRISS).
Those who are following the mission must be aware that the Webb telescope carried five layers of sun shields which it uses to prevent its scientific instruments from warming up from the Sun’s heat. NASA says that the sun shields have helped a lot in cooling down the instruments but further cooling will take place in the coming days. However, Webb’s Mid-Infrared Instrument (MIRI) would require cooling as low as -266° C, which will be done through a special refrigerator called the ‘cryocooler’.
The agency revealed that while the instruments will be subjected to cooling, the telescope will enter its orbit, the second Lagrange point (L2), in the next two weeks. Once in orbit, the scientists will align the 18 segments of Webb’s golden mirrors by moving them using motors as seen in the animation below. This alignment will ensure that the 21-foot-tall mirror made of 18 hexagonal mirrors serves as one and reflects the gathered light with precision. The cooling of instruments and the alignment of mirrors will be followed by calibration of each of Webb’s four instruments
With the James Webb Telescope now fully open with all mirrors in place and a sun shield protecting it from the heat of the Sun, Moon, and Earth the observatory is in a cooling down phase. The telescope after successfully completing over 50 major deployments, has entered into its commissioning phase as it continues to cruise towards its intended orbit.
The James Webb Telescope is traveling to the second Lagrange point (L2) nearly 15,00,000 kilometers away from home. The unfolding of the telescope took over 15 days with the team opening up the sun shields, secondary mirrors, and then the two folded segments of the primary mirrors.
The two wings of Webb’s primary mirror had been folded to fit inside the nose cone of an Arianespace Ariane 5 rocket prior to launch.
“Words can’t describe the pride and excitement the Webb team is feeling right now. From engineers to scientists to IT staff to graphic designers to administrative personnel (and more!), we are all overjoyed with the incredible successes of the observatory to date,” Alexandra Lockwood, project scientist for Webb science communications said.
What happens next?
In the next two weeks, engineers and scientists will work in tandem to move each of the 18 primary mirror segments, and the secondary mirror, out of their launch positions. The detailed optical mirror alignment process is about a three-month process. In parallel, as temperatures cool enough, instrument teams will turn on their instruments and begin each instrument's commissioning process.
The five months of commissioning ahead will include further cooling of the entire observatory, and of the Mid-Infrared Instrument, in particular, checking and then aligning the secondary and 18 mirror segments into a single coherent optical system, first with the NIRCam instrument and then with all instruments individually and in parallel, and calibrating of each of the four instruments and their many scientific modes.
“The novelty and variety of science that this observatory can produce requires thousands of things to be checked ahead of time. But rest assured that this summer will sizzle with the hot (nay cold?) observations we will soon be sharing!” Lockwood added.
Webb will also undergo a third mid-course correction burn one of three planned to place the telescope precisely in orbit around the second Lagrange point. This is Webb’s final orbital position, where its sun shield will protect it from light from the Sun, Earth, and Moon that could interfere with observations of infrared light.
Webb is designed to peer back over 13.5 billion years to capture infrared light from celestial objects, with much higher resolution than ever before, and to study our own solar system as well as distant worlds.
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