This Sunshield Will Keep the World's Most Powerful Space Telescope from Frying

The James Webb Space Telescope, scheduled for launch in 2018, will be the most powerful time machine ever built. From its perch in Lagrangian point 2, a position located far past the Moon, the telescope will be able to peer into the birth of the universe, and characterize the atmospheres of alien planets with unparalleled precision.

The observatory's unique superpowers would not be possible without its largest and most epic component: the heat-blocking protector known as the JWST sunshield. The shield, which is about the size of a tennis court, will be positioned between the telescope's delicate instruments and the Sun, making it look kind of like a space-aged divan for the Webb to relax on. But though its purpose and outward appearance seem straightforward, everything else about the sunshield is extreme.

The most obvious example is the temperature difference between the shield's two sides. The Sun-facing side will reach temperatures of about 200 degrees Fahrenheit, while the side facing the telescope will be a frigid minus 388 degrees, barely above absolute zero.

"It's a near 600 degrees Fahrenheit difference from the hot side to the cold side," Scott Willoughby, James Webb Space Telescope program manager and vice president of Northrop Grumman Aerospace Systems, which is building the JWST, told me over the phone.

"If the sunshield was the equivalent of an SPF that you would pull off the shelf at your local drug store," he added, "it would be one million SPF."

That is a pretty effective sunblock by any metric, and it's even more impressive considering the sunshield is made up of only five layers, each about as thick as a human hair.

"It's a pretty incredible design," said Willoughby. "The layers are made out a material called Kapton, which is an incredibly thin and very strong material. We coat it with materials that enable the layers facing the Sun to maximize the reflection of the Sun."

About 90 percent of the heat and light is thus blocked by the first layer, and the remaining 10 percent is further dissipated in the space between the first and second layer. Each successive Kapton sheet reflects and vents out more heat, until the chilly target temperature of minus 388 degrees is finally reached at the fifth layer. Sunshine: defeated.

The telescope requires such bitterly cold temperatures because it is specialized to capture infrared light. "Infrared is a heat signature that everything gives off, so this juicy information from 13 and a half billion years ago has been shifted. We need to be colder than the light we're looking for," Willoughby said, which necessitated the development of the gargantuan shield.

The sunshield may be ungainly, but its payoff will be huge. The JWST will be 100 times more powerful than the Hubble Telescope, with seven times the collecting area. On top of that, no area of the universe will be blocked from its vision.

"With the combination of our slew—our ability to point left, right, up, and down—and our one year orbit around the Sun, we can get the entirety of the universe," explained Willoughby.

That includes highly precise estimates of the exoplanetary atmospheric composition, including searching for biomarkers.

"[Webb's] near-infrared spectrograph can look for biomarkers, or signs of life," he said. "Our ability to look at atmospheres enables us on that path towards detecting life in the universe by finding, hopefully, telltale signs of life we know. That's going to be an amazing day."

As tantalizing as it is to daydream about the capabilities enabled by the shield, the JWST team has much more testing to do first. In July of this year, the JWST team completed the first full test deployment of the shield, an event that was 12 years in the making, according to Willoughby.

Timelapse of July's test deployment.

Indeed, testing the sunshield is as much of minefield of challenges and lateral thinking as designing and building it. No thermal vacuum chamber in the world is big enough to hold it, so the JWST team build a replica that was a third of the size, and adjusted all their variables to test that instead. "We had to get very creative," said Willoughby.

Going forward, the component parts of the Sunshield will be tested, and then integrated into the complete observatory in 2017 or 2018. After that, the final observatory will also have to go through a number of experiments, including some time on a "shaker table," which will simulate the turbulent experience of being blasted into space on an Ariane 5 rocket.

But the most important test will, of course, be the deployment itself, which will take place during the JWST's trip to its final orbital destination. Over 29 days and one million miles, the sunshield will unfurl from its tiny clamshell package, pulling the five layers apart and taut in preparation for the telescope's arrival. By the time the observatory settles down in its comfy L2 digs, it will be ready to be calibrated, oriented, and ultimately, handed over to the scientists who have been itching to use it since it was first conceived in 1996.

Sunshield deployment sequence.

One of the most interesting byproducts of the sunshield's inventive design and laborious testing process is the questio of what to do next. If the JWST will upstage Hubble so dramatically, then what kind of telescope will one day upstage JWST? As I talked with Willoughby about the Webb's ability to detect alien biomarkers, he casually brought up a scenario that would make any self-respecting futurist's jaw drop.

"We're not going to be able to direct-image life on a planet," he said of the JWST. "We're not that powerful."

"But maybe the next telescope will be, where it will actually see landmasses or liquid," he added. "That's the vision of the future."

Perhaps it's ill-advised to already be looking beyond the JWST and its spectacular shield, given how revolutionary its design and capabilities will be. But the idea that building and launching it might eventually lead to close-ups of exoplanets, down to their continental features and contours, is downright enticing. Given the JWST's incredible capabilities, it doesn't seem that outlandish either. Looks like we're going to need a bigger sunshield.