NASA Begins Tensioning Webb Telescope’s Vital Sunshield

NASA spent 20 years designing and building the James Webb Space Telescope on Earth, and it left the planet behind forever on Christmas Day 2021. Since then, NASA has been working to unfurl the observatory, which was bundled up to fit inside the Ariane 5 launch vehicle. After a brief delay over the weekend, the team has started the painstaking process of tensioning the sunshield. This is one of those make-or-break parts of Webb — if the sunshield doesn’t deploy correctly, the telescope may never work as intended.

Getting Webb into space was a nerve-wracking experience for all involved, but that was only the beginning. Hundreds of tasks need to go right over the next few weeks as Webb deploys all its hardware. Shortly after launch, NASA confirmed deployment of the solar panel and the primary communications array. Webb also extended its tower assembly (where the mirrors attach to the spacecraft) and the momentum flap, which counters the force of solar wind on the solar panel. That brings us to the sunshield, which began deploying last week.

Webb requires a sunshield because it was designed to operate in the mid-infrared. Hubble, by contrast, operated mainly in the visual spectrum. Infrared wavelengths of light can reveal much older, dimmer objects, as well as objects like protoplanets hiding behind dense clouds of dust and gas. To observe in the infrared, Webb needs to keep its instruments cool, thus the sunshield.

Last week, the spacecraft extended two support arms for the shield, one on the front and the other on the rear. Then, the team activated the left and right booms that opened the shield into its distinctive diamond shape. Rather than move immediately to the tensioning step on Sunday, NASA opted to assess the observatory’s status — they only get one chance at this.

The sunshield consists of five layers (see above) of polyamide film known as Kapton. To cool the instruments as designed, the layers need to be tensioned to create a small gap between each one. NASA started on Monday with just the first layer, triggering embedded cables to pull the ultra-thin material taut. It will take two or three days to get all five layers aligned, but that will take care of one of the most perilous parts of the deployment process.

It will take several more weeks to get Webb into its final configuration, but it won’t be ready to start operating when it reaches the Earth-Sun L2 Lagrange point. Outside the moon’s orbit, Webb will be able to block solar radiation with the sunshield and cool down its instruments over the course of months. NASA will also need to conduct tests and calibration on the observatory before it starts doing science. We should get the first Webb data around the middle of 2022.