The James Webb Space Telescope Is Deployed: But How Did Engineers Design for its Biggest Challenge?

The 70-foot space telescope is the largest and most complex ever built.

Currently, the James Webb Space Telescope (JWST) is fully deployed and orbiting it the Second Earth-Sun LaGrange point (L2) while undergoing some final alignments and setup. But in early January 2022, it unfurled its 70-foot sunshield—that’s about the size of a tennis court—marking a major engineering first and a critical moment in the JWST’s mission. The task was particularly challenging because it had been impossible to test how the telescope would deploy in space during its development.

The sunshield protects the telescope from external sources of light and heat. (Image courtesy of NASA.)

The sunshield protects the telescope from external sources of light and heat. (Image courtesy of NASA.)

The sunshield is a mission-critical component of the JWST, which is the largest, most complex and powerful space telescope ever built. The telescope has five layers that will protect its sensitive instruments from the light and heat of the Sun, Earth and Moon. Each plastic sheet is about as thin as a human hair and is coated with reflective metal that will give the satellite protection of more than SPF 1 million. The sunshield reduces Sun exposure from over 200 kilowatts of solar energy to a mere fraction of a watt. This protection is essential: the Webb’s scientific instruments need to maintain temperatures of 40 kelvins, or under minus 380 degrees Fahrenheit, so that the JWST can observe and study faint infrared light.

Had the sunshield failed to deploy properly, a project that had taken decades to develop would have ended in an unfixable failure. Unlike the Hubble Space Telescope, which was designed to allow for repairs and upgrades in orbit, the James Webb will be too far away to fix any problems.

Webb’s sunshield is positioned between the Sun/Earth/Moon and the telescope. Webb’s orbit at L2. (Image courtesy of NASA.)

Webb’s sunshield is positioned between the Sun/Earth/Moon and the telescope. Webb’s orbit at L2. (Image courtesy of NASA.)

Under normal circumstances, a first-of-its-kind system like the sunshield would have gone through extensive testing. And although the sunshield was tested thoroughly on the ground, there was no way to replicate zero gravity and the vacuum of space on Earth to test how it would deploy in those conditions.

So, the engineers at Northrop Grumman who designed the sunshield relied heavily on digital modeling to approximate how the telescope would behave in the vacuum of space and to anticipate any issues that may come up.

“For instance, when the telescope is all packed in and stowed in the launch vehicle, it’s a controlled chaotic, violent event,” said Javier Lopez, a structural analyst at Northrop Grumman who worked on Webb. “We made sure that it will stay in one piece during that event.” The sunshield was folded up like origami—a total of 344 times—to fit inside the payload fairing.

Cross-section of the telescope’s sunshield. (Image courtesy of NASA.)

Cross-section of the telescope’s sunshield. (Image courtesy of NASA.)

Another factor that couldn’t be tested on Earth was the significant thermal gradient between the side of the sunshield that faces the sun and the side that faced away from it. The sun-facing side could see temperatures of 350 degrees Fahrenheit, while the other side needs to keep the telescope’s instruments near absolute zero.

“We spend a lot of time simulating and validating on Earth so that we can accurately quantify those events. We have to design and qualify the spacecraft to that environment,” said Lopez. “We have to verify and prove that once it’s all deployed and stretched out in space, it will perform the intended use even at those extreme temperatures.”

Northrop Grumman spent years developing analytical methods, 3D simulations and large 3D models to validate the data from the simulations. The company used analytical computation to simulate the sunshield’s behavior on Earth and then tested the data with a physical model. While it wasn’t a gravity-free environment, the method still enabled the engineers to extrapolate the model to a zero-g scenario and predict how the structure would behave in space. They used finite element analysis to predict how objects would react to physical pressures such as vibration and heat.

The aerospace company turned to Ansys to help produce the simulations. Systems Tool Kit (STK) Astrogator, made by Ansys subsidiary AGI, was used to build complex design reference missions (DRMs). The DRMs were used to model the complex gravitational activity at the destination point of the satellite (L2, where the gravitational pull from Earth and the Sun balance each other out, about 930,000 miles from Earth). AGI’s Orbit Determination Toolkit (ODTK) was used to perform operational orbit determinations.

To model the impact of solar radiation on the sunshield itself, the James Webb’s engineers used a custom solar radiation pressure plug-in for ODTK and inserted a proprietary model into the toolkit’s advanced estimation algorithms.

Northrop Grumman performs a test on Earth before launch. (Image courtesy of NASA.)

Northrop Grumman performs a test on Earth before launch. (Image courtesy of NASA.)

Once the models were created, extensive ground testing took place.

“It was so huge to have the ground testing because all of these interactions were brand new to us … to learn so much through the ground tests of how all of these soft structure parts interact… it’s a balancing act,” said Hillary Stock, deployment specialist for the sunshield at Northrop Grumman. “To have that opportunity, sort of a sandbox, to develop a soft structure deployable system, was invaluable.”

And testing on the ground was key, and unlike some elements of Webb, the sunshield could be taken through multiple deployment tests on the ground.

“I guess our benefit was that we had multiple of those deployments that we were able to perform on the ground,” said Joe Sprofera, dynamics lead for the JWST program at Northrop Grumman. “There was a lot of analytical predictions that were basically confirming on the ground with that one-G to zero-G analytical prediction that sets everything going on while we’re pushing out a boom or while we’re running motors to bring the layers up into position.”

As thorough as the team was with its simulation and ground testing, when the JWST launched there was still a sense of uncertainty about whether the sunshield would behave as the models predicted. The models turned out to be spot on.

“When we got into the on-orbit deployments having not done a zero-G deployment before, we [really had] a minimum predict and a maximum predict,” said Stock. “We [were] just hoping to fit somewhere within our predictions, and to see us coming right in dead center as we would hope and expect was a great moment.”

The JWST deployment sequence.

In fact, the sunshield deployed flawlessly over the span of eight days. First, the forward and aft pallet structures unfolded, bringing the JWST to its full 70-foot length. Then the Deployable Tower Assembly unfolded, separating the telescope and instruments from the main body of the spacecraft. This gave the sunshield enough room to fully deploy. Then the aft momentum flap and membrane covers were released and deployed; this was followed by the mid-booms, which deployed and expanded perpendicular to the pallet structures. This allowed the sunshield to stretch out to its full 47-foot width. Finally, the sunshield was fully tensioned and locked into position.

Deploying the sunshield took 139 of Webb’s 178 release mechanisms, 70 hinge assemblies, eight deployment motors, about 400 pulleys, and 90 individual cables.

“The sunshield is remarkable as it will protect the telescope on this historic mission,” said Jim Flynn, sunshield manager at Northrop Grumman. “This milestone represents the pioneering spirit of thousands of engineers, scientists, and technicians who spent significant portions of their careers developing, designing, manufacturing, and testing this first-of-its-kind space technology.”