The James Webb Space Telescope Just Cleared Its Most Challenging Hurdle

The tennis court-sized sunshield fully unfurled itself this week, accomplishing the riskiest and most complicated aspect of the telescope’s deployment

Part of the primary mirror—a collection of gold-plated hexagons—are held above the sunshield. The sunshield has five thing layers that look like foil, and they're stretched out in a rectangular shape.
The telescope has five layers that dissipate heat from the sun. The sunshield's outer layer can reach 230 degrees Fahrenheit, and the last can drop to -394 degrees. NASA/Chris Gunn

So far, so good for the James Webb Space Telescope (JWST). Since it launched on Christmas morning, scientists and space nerds across the world have been nervously awaiting updates, and it just cleared a major milestone: unfurling its tennis court-sized sunshield, Joe Palca reports for NPR.

Scientists hope that this telescope will enhance our understanding of the universe, but for that to happen, there is very little room for error with its deployment. Unrolling the sunshield was the riskiest and most complicated part of the telescope's journey, and ground controllers cheered in celebration once it was in the clear, Marcia Dunn reports for the Associated Press (AP).

"Thousands of parts had to work with precision for this marvel of engineering to fully unfurl," Gregory L. Robinson, Webb’s program director at NASA, says in a press release. "The team has accomplished an audacious feat with the complexity of this deployment—one of the boldest undertakings yet for Webb."

James Webb Space Telescope Deployment Sequence (Nominal)

Of the more than 300 different ways the telescope could fail, 70 to 75 percent of those are cleared now that the sunshield is in place, Webb project manager Bill Ochs tells Ashley Strickland for CNN.

"The membrane tensioning phase of sunshield deployment is especially challenging because there are complex interactions between the structures, the tensioning mechanisms, the cables and the membranes," James Cooper, the Webb sunshield manager, says in a statement. "This was the hardest part to test on the ground, so it feels awesome to have everything go so well today."

The sunshield had to be folded up to fit inside the rocket that launched JWST. It took eight days to fully unfold and stretch the sunshield, and the last layer was secured on Tuesday around noon, CNN reports.

The telescope has five shiny, foil-like, ultra-thin layers that dissipate heat from the sun since the telescope only functions at extremely low temperatures. The sunshield's outer layer can reach 230 degrees Fahrenheit, and the heat seeps out in the space between each layer. Ultimately, the layer closest to the telescope will drop to minus 394 degrees Fahrenheit, Rebecca Ramirez reports for NPR's Short Wave.

An artist conception of the telescope in space. The background is dark with twinkly stars. The telescope's sunshield in the foreground reflect pink and purple light, and the gold hexagonal pieces of the primary mirror are above it.
The small, secondary mirror extends far in front of the primary mirror. It'll reflect light from the large mirror to the telescope.  NASA GSFC/CIL/Adriana Manrique Gutierrez

Once the sunshield was finished, the telescope started configuring its secondary mirror, which clicked into place on Wednesday. It's a round mirror—around 2.5 feet across—that extends in front of the primary mirror held at the end of three long beams. Its job is to bounce reflected light from the large, primary mirror and channel it into the telescope, George Dvorsky reports for Gizmodo.

Now that it's in position, the primary mirror will start to unfold over the next couple of days. It is more than 21 feet across, and—like the sunshield—was too large to fit in the rocket. It is comprised of 18 hexagonal pieces that will need to fit perfectly together to properly reflect light to the telescope.

Once the 18 pieces are in place, they'll take around 100 days to cool off, and by then the telescope will have reached its spot in space—930,000 miles away from Earth. After that, it'll take more time to finely align each segment of the mirror so the 18 pieces can act as one seamless unit. Scientists expect their first photos from the telescope this summer, Tereza Pultarova reports for

"This is the first time anyone has ever attempted to put a telescope this large into space," Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate, says in the press release. "Webb required not only careful assembly but also careful deployments. The success of its most challenging deployment—the sunshield—is an incredible testament to the human ingenuity and engineering skill that will enable Webb to accomplish its science goals."

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