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The James Webb Space Telescope (JWST) has partially deployed its sunshields, which might extend the mission's duration beyond what was originally envisaged.


Anne Agi

1/2/2022 3 min read

In a series of tweets on the 28th of December, 2021, NASA announced with glee that JWST's forward sunshield had been successfully deployed. They declared:

“Our telescope is blossoming in space like a flower! This is the start of a significant step of #UnfoldTheUniverse: the deployment of our sunshield.” First and foremost, what is our sunshield?

  • 5 layers

  • Opens to the size of a tennis court

  • Protects Webb's optics from the sun

 This marks the start of a major phase to #UnfoldTheUniverse: our sunshield deployment. ....Right now we just successfully completed the first step: unfolding the forward sunshield pallet. Think of Webb's pallet as a cake stand that will hold 5 layers of sunshield - the cake's layers, if you will.

In a further tweet on the 29th of December, 2021, they added: "And we just confirmed that our aft (back) sunshield pallet has successfully opened up as well".

NASA tweets about it here:

December 28, 2021 — NASA Webb Telescope (@NASAWebb)

Much of the world exhaled a sigh of relief after the JWST's successful launch on Christmas Day. However, there is still a long way to go for the team in charge of deploying the world's largest and most expensive space telescope, and many obstacles that could hinder mission success. Each potential stumbling block overcome is a win which is why NASA is excited at this deployment. The JWST is currently halfway through the deployment of its sunshields, which is a time-consuming and critical process that will take at least five days. 

Eventually the JWST should look like this. But the vital sunshields are only half deployed now, after which the mirrors will be placed in position. Image credit: NASA GSFC/CIL/ADRIANA MANRIQUE GUTIERREZ

The JWST's mirror is seven times the size of the Hubble's, which is part of what makes it so powerful, but that's not the only reason it's been such a difficult project to build and deploy. The JWST will observe almost entirely in the infrared section of the spectrum, bridging a gap in our understanding of the universe that has arisen as a result of research focusing on light visible to our eyes. However, seeing into the infrared requires shielding from the sun's heat, which necessitates the use of massive, difficult-to-deploy sunshields.

Five membranes are included in the shields, as well as wires to support them and release mechanisms. There is minimal tolerance for mistake because the JWST's orbit — around the Sun, nearly 1.5 million kilometers (1 million miles) from Earth — basically bans astronauts from tugging on blocked wires or hitting items that don't operate properly. It took four hours to deploy forward. The mission may have been ruined if the operation had failed, so relief is palpable.

However, the process does not end with the sunshields being lowered. Deployable Tower Assembly was the next phase, which has now been done. This separates the telescope from the rest of the spaceship, allowing it to maintain its operating temperature of 40 K (-233oC or -388oF).

The sunshield cover release, mid-boom extension, and setting the proper tension in the sunshield layers are still to come.

According to NASA, each stage takes hours because so many steps are involved. The overall process took several hours for each because of the dozens of additional steps required, according to the agency's Webb blog. They explained that “The actual motion to lower the forward pallet from its stowed to its deployed position took only 20 minutes, and the lowering of the aft pallet took only 18 minutes, the overall process took several hours for each because of the dozens of additional steps required.” “These include closely monitoring structural temperatures, maneuvering the observatory with respect to the Sun to provide optimal temperatures, turning on heaters to warm key components, activating release mechanisms, configuring electronics and software, and ultimately latching the pallets into place.”

The deployment of the sunshield is the most difficult, but not the last, step before operations may begin. The mirrors must be deployed after the sunshields have created a safe cool environment, commencing with the secondary and then the primary's component wings. Once the telescope is fully unfolded, a fuel burn is required to propel it to L2, the Lagrange Point, which is the opposite of the Sun from Earth. for more on the sunshields see: See

Between these stages, NASA had some good news of its own: if the deployment goes well, the JWST will be able to function for longer than expected. Because the launch and first course adjustments went so successfully, less propellant was utilized than expected. This frees up more space for the orbital corrections and orientation modifications that must be made throughout the telescope's lifetime of operation. There is enough propellant for more than ten years, rather than the baseline five years considered the least to justify the mission.

This is the start of a success story for science.

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