There seemed to be a bit of new news in the James Webb Space Telescope (JWST) every few days earlier this year, but we haven’t heard much from the Revolutionary Observatory lately. Because it’s getting cold – literally. The telescope cannot begin the work of science until its instruments reach the correct operating temperature. NASA has now reported that the coolest device on the web has reached its desired temperature, marking another step towards becoming fully operational.
Unlike Hubble, JWST was designed to peer into the mid-infrared portion of the electromagnetic spectrum. Any mistaken heat from terrestrial sources or the sun can destroy such observations. That’s why the spacecraft was deployed outside the moon’s orbit at the Earth-Sun L2 Lagrange Point. A few months ago, Webb successfully deployed its Sunshield, which allows the interior to cool to their desired temperature, even from zero.
NASA says the Web’s Mid-Infrared Instrument (MIRI) has reached temperatures of just 7 Kelvin (-266 Celsius, -447 Fahrenheit). Initially, MIRI and other instruments of the telescope hit 90 kelvins in the power of a tennis-court-sized sunshield. To get it everywhere where it currently sits, the team has activated the spacecraft’s electric cryocular. To get there, the cooler had to successfully cross the “pinch point”, the range of about 15 Kelvin where the cooler’s heat removal capacity is minimal. Several time-critical valve and compressor operations were started to quickly fill the gap and get the observatory back to where it is now.
All four science devices on the web are leaning towards infrared, so they need to be kept cool. However, MIRI is special. Since it is designed to scan longer infrared wavelengths, it is more sensitive to an effect known as dark current. It is a tiny electric current generated by atomic vibrations. Dark current may appear on detectors as a valid signal, but keeping them cool reduces the effect. This is why MIRI needs to be cooler than the rest of the telescope, and at 6.4 Kelvin, this is exactly where it needs to be.
Previously, NASA had completed the alignment and stacking of the telescope’s versatile mirror, and now the team could begin calibrating MIRI. It involves capturing images of familiar objects to ensure the operation and functionality of the device. Other devices have to go through similar operations.
Glad to see the web cross one milestone after another, especially after all those years of delays on Earth. When it is fully launched, the web will be able to return to the dawn of the universe where objects are too dim to even see Hubble. This can also be important in the case of exploratory exoplanets, which are similarly obscure signals next to stars. NASA expects the first science operation to begin this summer.