Science

Why deploying the James Webb space telescope’s sunshade takes so long

NASA’s James Webb Space Telescope has been deploying its massive parasol for three days, and it still has about three days to go.

The $ 10 billion Webb was launched on Christmas Day (December 25) to look for signs of heat from the early universe. To pick up these weak signals, the observatory’s optics and instruments must be kept extremely cool, and that’s where the sunshade comes in.

The five-layer structure will reflect sunlight and radiate heat extremely efficiently, allowing Webb to maintain its “cool side” at a freezing temperature of minus 370 degrees Fahrenheit (minus 223 degrees Celsius), if all goes according to plan. . The “hot side” of the observatory facing the sun, by contrast, will be around 230 degrees F (110 degrees C), NASA officials wrote in a Webb sunscreen explainer.

Live Updates: NASA’s James Webb Space Telescope Mission
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The kite-shaped parasol measures 69.5 feet long by 46.5 feet wide (21.2 by 14.2 meters). That’s too big to fit inside the payload fairing of any currently operating rocket, so the structure was raised in a very compact configuration and now must be deployed in space.

That operation is incredibly complex, involving many different, time-consuming steps to bite your nails.

“Webb’s sun visor assembly includes 140 release mechanisms, approximately 70 hinge assemblies, eight deployment motors, bearings, springs, gears, approximately 400 pulleys and 90 cables totaling 1,312 feet [400 m]”Webb spacecraft systems engineer Krystal Puga said in” 29 Days on the Edge, “a video about Webb deployments that NASA released in October.

“All of this just to keep the sunshade under control while it is deployed,” added Puga, who works for aerospace company Northrop Grumman, the prime contractor for the Webb mission.

That deployment began on Tuesday (December 28) with the sequential deployment of two pallets containing the sunshade structure. Webb took the next step on Wednesday (December 29), extending his deployable tower assembly, a move that, among other things, created space for the parasol membranes to deploy.

Two more milestones occurred on Thursday (December 30): Webb launched the canopy that had protected the parasol during ground operations and launch and also deployed its “aft thrust fin”, which will help the observatory maintain its orientation and position without using too much fuel.

“As photons from sunlight hit the large surface of the sunshade, they will put pressure on the sunshade and, if not balanced properly, this solar pressure would cause rotations of the observatory that must be accommodated by its reaction wheels,” said Alise. Fisher, a NASA public affairs specialist. wrote in a blog post Thursday. “The aft thrust fin will navigate with the pressure of these photons, balancing the sunshade and keeping the observatory stable.”

Deployment action, which can follow here, will keep coming. Webb is expected to deploy its five sunscreen membranes on Friday (Dec. 31), which it will accomplish by extending two barriers. Members of the mission team will get the membranes to the proper tension over the weekend, which could conclude with this procedure, and the deployment of the parasol in general, starting Sunday (January 2).

Then the focus will shift to Webb’s primary and secondary mirrors, both of which are scheduled to be fully deployed by January 7 or so.

NASA officials and members of the Webb team have emphasized, however, that these timelines are flexible. Some steps may take longer than anticipated, so don’t panic if the observatory doesn’t seem to be exactly hitting the mark (although it has done quite well so far).

We should all take a moment to celebrate what Webb has accomplished so far and wish the mission team luck in the steps that remain.

“The Webb Observatory has 50 major deployments … and 178 release mechanisms to deploy those 50 parts,” said Webb mission systems engineer Mike Menzel of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, at “29 Days on the Edge “.

“Each of them has to work,” Menzel said. “Deploying Webb is without a doubt the most challenging spacecraft activity we have ever undertaken.”

These deployment steps are occurring as Webb navigates toward his destination in deep space, a gravitationally stable point 930,000 miles (1.5 million kilometers) from our planet called Sun-Earth Lagrange Point 2 (L2). The observatory will arrive there about 29 days after launch, and will be put into orbit around L2 with precise engine combustion.

But Webb won’t be ready to start observing the cosmos as soon as it arrives, far from it. It will take about five more months to precisely align the 18 segments that make up the telescope’s 21.3-foot-wide (6.5 m) primary mirror and calibrate its four science instruments. Regular science operations are expected to begin in late June or early July 2022.

Mike Wall is the author of “Out There” (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for extraterrestrial life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or on Facebook.

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