NASA’s next-generation James Webb Space Telescope has successfully deployed its sunshield — a critical feature the observatory will use to keep its instruments extra cold during the course of its mission. The unfurling of the sunshield marks the end of perhaps the most complicated deployment the observatory must pull off in order to properly function while in space.

“This is a really big moment,” Bill Ochs, the project manager for JWST at NASA’s Goddard Space Flight Center, said to the mission team after the deployment was complete. “I just want to congratulate the entire team. We still got a lot of work to do but but getting the sunshield out and deployed is really, really big.”

The James Webb Space Telescope, or JWST, is NASA’s powerful new space observatory that launched on December 25th after roughly 25 years of development. Often considered the successor to the Hubble Space Telescope currently in orbit around Earth, JWST promises to provide even more power and an enhanced capability to see distant, faint objects in our Universe. Astronomers hope to use JWST to peer back in time and see some of the first stars and galaxies that formed just a few hundred million years after the Big Bang.

But in order to observe the ancient Universe, JWST has to go through a complex unfolding process first. The telescope was far too large to launch to space in its final configuration, so mission designers crafted the telescope to unfold after launch. The deployment relies on hundreds of mechanisms and moving parts, and everything has to go right in order for JWST to function. Along the way, there are up to 344 single-point failures, deployments without any backups that must execute as designed or else they could jeopardize the entire mission.

Part of the unfolding process entailed deploying JWST’s sunshield. JWST observes infrared light, a type of invisible light that is associated with heat. Because of this, the telescope must remain extremely cold in order to properly function, operating at roughly -370 degrees Fahrenheit. The sunshield, comprised of five thin reflective layers of a material called Kapton, is designed to prevent the Sun’s heat from cooking the telescope too much.

The deployment of the sunshield was an extremely complex event; the layers are incredibly thin membranes that had to remain intact. Up to 107 release mechanisms were used to unfurl the layers, and each mechanism had to work as planned in order for the sunshield to completely open up. Once the layers unfurled, the spacecraft then had to draw them taut, a bit like sails on a sailboat.

The sunshield deployment took a little more than a week to complete, a bit longer than originally planned. NASA had tentatively scheduled the process to take about six days, but the JWST team took a pause over the New Year weekend to both get some rest and pore over the data they were receiving from the spacecraft. There were also a few problems they had to work on along the way due to some unexpected temperature readings and equipment issues. “We are still in the getting-to-know-you phase with the telescope,” Ochs said during a press conference the day before deployment ended. “Orbital satellites will always be a little bit different on orbit than they are on the ground.”

The first problem was a small issue with JWST’s solar arrays, which generate power from the Sun that the telescope needs in order to function. A factory preset of the solar arrays was limiting their power output, but Northrop Grumman rebalanced the arrays based on the temperatures they were experiencing in space. That seemed to fix the problem, and JWST is getting enough power now to function properly. The other issue revolved around the motors used to release the sunshield and help tension the layers. They were running a little bit hotter than the JWST team expected, so mission engineers slightly reoriented the observatory to reduce the sunlight hitting them. That helped to cool the motors off ahead of their planned use.

Now that the sunshield is unfurled, some of the most nail-biting moments of JWST’s deployment are in the past. NASA says that between 70 to 75 percent of the single-point failures have officially been completed. “That is huge within the first week and a half or so of the spacecraft being in operation,” Ochs said during the press conference.

But there are other milestones yet to come for the telescope. Notably, the observatory still has to deploy segments of its primary mirror, the main tool it will use to collect light from distant galaxies and stars. That crucial event is set to happen in roughly a week, and like all the deployments up until now, it must execute perfectly in order for JWST to fulfill its job.

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