JAMES WEBB SPACE TELESCOPE
How Northrop Grumman Prepared the Webb Sunshield to Unfold Flawlessly in Space
By Brooks McKinney, APR
How do people on the ground unfold a five-layer sunshield the size of a tennis court orbiting in space? With practice. A lot of practice.
A little over a week after NASA’s James Webb Space Telescope (Webb) launched, a team of NASA, Northrop Grumman and other mission partner engineers completed the deployment and tensioning of the telescope’s sunshield from the Mission Operations Center in Baltimore, Maryland. Made of layers of chemical polyimide film, the structure shields Webb’s infrared telescope and science instruments from heat and light generated by the Sun, Earth, or even the observatory itself that could make the telescope too hot to work properly. And the shield has a big job, since the temperature of Webb must not rise above -380 degrees Fahrenheit.
There was only one chance to get it right, so for years, engineers prepared using an intricate model of the sunshield developed at Northrop Grumman’s Space Park facility in California.
“I was quite relieved, but not surprised, when we successfully completed the sunshield deployment,” says Jeff Cheezum, the engineer who led Northrop Grumman’s design and development of the sunshield. “After testing every possible aspect we could think of, there was just no way it was going to fail.”
Building the Prototype
As Cheezum explains, when the Webb program began in 2003, there was no official plan to develop such an engineering model. However, it quickly became clear that one would be critical to mission success.
“During the preliminary design phase, the program went from having a bare-bones structure and a basic, simplified membrane to realizing that, ‘Hey, our engineering model actually needs to include all five layers,'” he says. “‘And that model needs to be as flight-like as possible, so we can practice on an exact prototype of the flight sunshield.'”
The sunshield engineering model is a full-scale, fully functional prototype of the flight sunshield. It allowed Cheezum and his team to define and practice all the mechanical and engineering tasks they’d have to perform when building and deploying the flight version of the sunshield.
“The engineering model includes all the key mechanisms and components that must articulate and open for us to fully deploy the sunshield,” Cheezum explains. “It also includes the membrane tensioning systems with all ninety cables that allow us to tension all five sunshield layers and create the required insulating space between each of the layers.”
Practice Makes Perfect
Cheezum’s team used the engineering model to refine and perfect the design of the sunshield’s membranes as well as the structures used to attach them to the core structure of the Webb spacecraft bus. The first five membranes produced, aka “template” membranes, became the basis for the engineering model.
According to Cheezum, perhaps the most essential job of the engineering model was to help his team learn how best to fold, stow and deploy the sunshield.
“We stowed and deployed the sunshield multiple times using the engineering model and several more times using the flight sunshield,” he recalls.
Those rehearsals also revealed that the membrane coatings could start degrading after even minimal amounts of folding and unfolding — a condition that could potentially allow the telescope and instruments to overheat. Knowing this, engineers took appropriate steps to correct this.
Expecting Success, But Ready for Anything
During the on-orbit deployment of the sunshield, Northrop Grumman’s main deployment team sat with its NASA counterpart at the Space Telescope Science Institute (STScI) in Baltimore. The teams issued commands, then waited for telemetry from Webb to confirm the completion of each step. Cheezum’s team in Redondo Beach, California would then adjust the sunshield engineering model into that same configuration.
“If any technical issues developed during an on-orbit deployment step, we wanted to be ready to simulate that issue and troubleshoot it in real-time using our sunshield engineering model,” Cheezum explains.
Thankfully, the troubleshooting team saw only limited action.
With Webb’s sunshield now fully deployed, the future of the engineering model remains uncertain. It will remain in Space Park through the end of 2022, but after that, it will embark on its own voyage. Cheezum hopes the model will go on permanent public display at a museum, where the public can study it for years to come.
Cosmic Game Changer: Northrop Grumman and NASA’s James Webb Space Telescope
Read this fascinating three-part series on the creation of the James Webb Space Telescope.