James Webb Space Telescope enters 'cooldown period' after unfolding, NASA explains meaning

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.