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Following Webb’s Arrival at L2, Telescope Commissioning Set to Begin

Following Webb’s arrival at its orbital destination around Lagrange Point 2 (L2) on Jan. 24, the mission operations team began working its way through a critical series of steps: powering on all the science instruments, turning off heaters to begin a long cooldown process, and ultimately capturing the first photons on Webb’s primary camera to enable a months-long alignment of the telescope.

While the MIRI instrument and some instrument components were powered on in the weeks after Webb’s Dec. 25 launch, the team didn’t finish turning on the remaining three instruments – NIRCam, NIRSpec, and FGS/NIRISS – until the past few days.

The mission operations team’s next major step is to turn off instrument heaters. The heaters were necessary to keep critical optics warm to prevent the risk of water and ice condensation. As the instruments meet pre-defined criteria for overall temperatures, the team is shutting off these heaters to allow the instruments to restart the months-long process of cooling to final temperatures.

When NIRCam reaches 120 kelvins (approximately -244 degrees Fahrenheit, or -153 degrees Celsius), Webb’s optics team will be ready to begin meticulously moving the 18 primary mirror segments to form a single mirror surface. The team has selected the star HD 84406 as its target to begin this process. It will be the first object NIRCam “sees” when photons of light hit the instrument’s powered-on detectors. The process will essentially create an image of 18 random, blurry points of light. For the first few weeks of mirror alignment, the team will keep the instrument trained on the star while they make microscopic adjustments to the mirror segments; ultimately that collection of 18 blurry dots will become a focused image of a single star. Cooling of the telescope and instruments will also continue over the next month, with the near-infrared instruments ultimately reaching 37-39 kelvins. The cryocooler will cool MIRI to 6 kelvins in the following months.”

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