In major milestone, NASA's Webb space telescope fully deploys its critical sunshield
The James Webb Space Telescope, now more than 570,000 miles outbound from Earth, successfully finished tightening all five layers of its sunshield Tuesday, completing one of the most complex — and risky — steps in the $10 billion observatory's initial activation.
Using six motors connected to 90 stainless steel cables running through scores of pulleys, the fifth and final hair-thin layer making up the 70-foot-long, 54-foot-wide sunshade was pulled into place and snugly tightened just before noon EST, giving Webb its iconic multi-layer kite-like appearance.
"I can confirm the final latch signature, which indicates that all five layers of the sunshield are fully tensioned," an unidentified engineer reported to the mission operations team at the Space Telescope Science Institute.
"Significant milestone accomplished!" said Carl Starr, the mission operations manager, amid a burst of cheers and applause. "Job well done, sunshield team. Job well done."
Webb project manager Bill Ochs then came on the line to pass along his congratulations.
"We've still got a lot of work to do, but getting the sunshield out and deployed is really, really big," he said. "The JWST team is the best in NASA. There is, hands down, nobody better than what we have here. You guys should all take pride in all these accomplishments."
He closed by adding: "I'll just say what I put on Facebook last night when I shared the story, I just said the JWST team kicks butt. I didn't use the word 'butt,' I use another word, but I won't use that word here. Congratulations everybody!"
Hillary Stock, a sunshield deployment engineer with Northrop Grumman, Webb's prime contractor, summed up the feeling of many by saying: "Honestly, it went incredibly smoothly. I feel like we've all kind of been shocked that there's been no drama, it's been very smooth."
The Webb telescope, the largest and most powerful ever launched, is designed to capture light from the first stars and galaxies to begin shining in the aftermath of the Big Bang some 13.8 billion years ago.
To register that ancient radiation, stretched into the infrared by the expansion of space itself, Webb's mirrors and instruments must be cooled to within about 50 degrees of absolute zero, or nearly 400 degrees below zero Fahrenheit.
The telescope's designers came up with an ingenious, but very complicated, solution: a five-layer shield made up of thin layers of Kapton that could be folded up to fit inside a rocket's nose cone and then unfolded in space.
Once unfolded, pulled taut and separated, with gaps between each layer to allow residual heat to escape to the sides, the sunshade will constantly face the sun, blocking out the heat and light that otherwise would blind Webb's sensitive instruments.
The side of the shield facing the sun will experience temperatures as high as 260 degrees or so. But on the other side of the shield, on the side facing deep space, Webb's mirrors and instruments will be able to operate at some 390 degrees below zero.
The telescope will only be aimed at targets that can be observed from within the shadow of the sunshade, but given it orbit around the sun and its position relative to Earth, virtually the entire sky will be in reach over the course of a year.
Deploying the sunshade capped a dramatic week and a half for the Webb team, starting with launch on Christmas Day atop an Ariane 5 rocket from Kourou, French Guiana.
In quick succession, commands were sent to deploy the spacecraft's solar array, it's high-gain antenna and two long pallets that held the sunshade membranes, carefully folded and pinned in place, unfolding them fore and aft of Webb's primary mirror.
Then the telescope itself — the primary mirror and instrument housing — were elevated four feet above the plane of the sunshade to provide additional cooling and clearance for the shield's unfolding.
After protective covers were rolled away from the sunshade, two telescoping booms extended at right angles to the pallets on New Year's Eve, pulling out and unfolding the Kapton membranes as they went.
Engineers then spent two days fine tuning Webb's solar power system to improve performance and re-orienting the observatory slightly to cool down the sunshade tensioning motors. Work to pull the layers taut began Monday, starting with layers one through three. The final two layers were pulled tight Tuesday.
"I can tell you the mood was... hard to describe," said Stock. "It was a wonderful moment, there was a lot of joy, a lot of relief. But that was really because all of our telemetry was showing us everything was nominal."
Thanks to ultra-low temperatures, lighting conditions and added complexity, Webb is not equipped with any cameras that could have shown the various deployments as they were occurring. Instead, engineers relied on data from a myriad of sensors indicating cable tension, motor operation and a variety of other parameters.
The telemetry was fed into a computer that displayed Webb in a "live" animation that reflected the actual events in space. Data collected during years of dry runs on the ground matched the actual telemetry almost exactly.
"We've trained for this from 2016, when we first built these tensioning units, and we've been tracking it all the way through," Stock said. "And what we're seeing is really the heartbeat of this mechanism. And this mechanism is very intricate and very complex. But because of that, we're able to glean so much of the hardware position, the hardware resistance, and all of that from the motor telemetry.
"So we feel very, very good looking at these signatures, seeing the drops in current and understanding that that's related to the layer latched to the correct position. And everything lined up today."
With sunshade tensioning complete, the mission operations team will turn its attention to Webb's remaining deployments: two radiators, erection of the telescope's secondary mirror on an articulating tripod and the unfolding of two "wings" holding six of the primary mirror's 18 hexagonal segments.
Once the mirror elements are fully deployed, scientists will begin carefully aligning the optics, sending commands to motors on the back of each segment that can tilt, tip and slightly adjust curvature as required to achieve a razor-sharp focus.
After cool down to operating temperatures is complete, along with checkout and calibration of Webb's instruments, the first science observations are expected in about six months.
