Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab
With Webb’s first major structural deployments completed and the observatory’s Deployable Tower Assembly extended, we are taking a step back to learn more about Webb’s sunshield. Observatory Project Scientist Michael McElwain, from 
After launch and during the first month in space, on its way to the second Langrange point (L2), Webb will undergo a complex unfolding sequence. Credit: NASA, ESA, CSA, Joyce Kang (STScI)
“There are 50 major deployments that transform Webb from its stowed, launch configuration into an operational observatory. The sunshield deployment sequence started with the forward, then aft, UPSs’ mechanical release from the telescope and motorized lowering into position. The telescope and science instruments, mounted on a deployable tower assembly, were then mechanically released and raised. There is a momentum flap attached to the end of the aft UPS that is released and positioned, whose function is to balance the solar pressure on the deployed sunshield. The sunshield covers are released via retraction of membrane release devices and roll out of the way, readying the system for the deployment of the sunshield layers. The telescopic mid-booms sequentially push out from the spacecraft bus perpendicular to the telescope line of sight, pulling the folded stack of sunshield layers out into the final, but still untensioned, configuration. Finally, each sunshield layer is tensioned into position, starting with the Sun-facing layer first and finishing with the telescope-facing layer. The deployed sunshield begins a rapid cooldown of the telescope and the science instruments, but on-board heaters within the science instruments will be used to control their cooldown and prevent contamination.
“While these steps have been tested on the ground and operationally rehearsed in the Mission Operations Center, these critical activities must be executed for a successful mission. Best wishes to our team, and stay cool, Webb!”
– Michael McElwain, Webb observatory project scientist, NASA’s Goddard Space Flight Center