The James Webb Space Telescope team has fully deployed the spacecraft’s 70-foot sunshield, a key milestone in preparing it for science operations.
The sunshield – about the size of a tennis court at full size – was folded to fit inside the payload area of an Arianespace Ariane 5 rocket’s nose cone prior to launch. The Webb team began remotely deploying the sunshield Dec. 28, 2021, three days after launch.
Gregory L. Robinson, Webb’s program director at NASA Headquarters explained the significance of the event:
“Unfolding Webb’s sunshield in space is an incredible milestone, crucial to the success of the mission. Thousands of parts had to work with precision for this marvel of engineering to fully unfurl. The team has accomplished an audacious feat with the complexity of this deployment – one of the boldest undertakings yet for Webb.”
The five-layered sunshield will protect the telescope from the light and heat of the Sun, Earth, and Moon. Each plastic sheet is about as thin as a human hair and coated with reflective metal, providing protection on the order of more than SPF 1 million. Together, the five layers reduce exposure from the Sun from over 200 kilowatts of solar energy to a fraction of a watt.
This protection is crucial to keep Webb’s scientific instruments at temperatures of 40 kelvins, or under minus 380 degrees Fahrenheit – cold enough to see the faint infrared light that Webb seeks to observe.
The unfolding occurred in the following order, over the course of eight days:
- Two pallet structures – forward and aft – unfolded to bring the observatory to its full 70-foot length
- The Deployable Tower Assembly deployed to separate the telescope and instruments from the sunshield and the main body of the spacecraft, allowing room for the sunshield to fully deploy
- The aft momentum flap and membrane covers were released and deployed
- The mid-booms deployed, expanding perpendicular to the pallet structures and allowing the sunshield to extend to its full width of 47 feet
- Finally, at approximately 11:59 a.m. EST Tuesday, the sunshield was fully tensioned and secured into position, marking the completion of the sunshield deployment
The unfolding and tensioning of the sunshield involved 139 of Webb’s 178 release mechanisms, 70 hinge assemblies, eight deployment motors, roughly 400 pulleys, and 90 individual cables totaling roughly one quarter of a mile in length. The team also paused deployment operations for a day to work on optimizing Webb’s power systems and tensioning motors, to ensure Webb was in prime condition before beginning the major work of sunshield tensioning.
However, NASA still has a ways to go before the Webb telescope will be of use to scientists around the world. The world’s largest and most complex space science observatory has another 5 1/2 months of setup still to come, including deployment of the secondary mirror and primary mirror wings, alignment of the telescope optics, and calibration of the science instruments. After that, Webb will deliver its first images.