Slowly but surely, the James Webb Space Telescope is taking shape. Following its successful launch on Christmas Day 2021, NASA has been deploying systems one after another to get the telescope into its final configuration. Yesterday evening, NASA confirmed Webb’s massive sunshield was fully deployed, and now it’s following up by setting up the secondary mirror — you can think of it as the most expensive tripod in the solar system.
The sunshield unfurling began last week with the extension of several supports and booms that stretched out the five-layer Kapton assembly. Because Webb is designed to make observations in the mid-infrared, its instruments need to be kept extremely cold. That’s part of the reason it’s going all the way out to the Earth-Sun L2 Lagrange point past the orbit of the moon. Out there, it will be able to block solar rays with the shield and keep its internals frosty.
Listen in as @NASAWebb experts give an update following today’s successful deployment of the 5-layer, tennis-court-size sunshield in space: https://t.co/Bl5VHPN1dW
— NASA (@NASA) January 4, 2022
For the shield to work at maximum efficiency, NASA had to tension each of the five layers with a system of cables and pulleys. This system caused issues during ground testing. In fact, one of Webb’s numerous delays was due to tears in the shield from an early test. However, the team has now confirmed that all five layers have been tensioned successfully. This leaves a small gap between each layer, increasing the heat dissipation of the sunshield.
Of course, the sunshield is no good if the telescope itself doesn’t work. Webb’s primary mirror with its large hexagonal panels is well known, but that’s just one part of the telescope’s optics. After nailing down the shield, NASA moved on to the secondary mirror structure. Like most of the protruding bits, it was folded down for launch, and it’s every bit as essential as the primary mirror. Light hits the primary mirror first, and then it bounces to the secondary mirror. The secondary mirror is responsible for directing light into the spacecraft where tertiary and steering mirrors send it to the instruments.
CONFIRMED: “The world’s most sophisticated tripod” has not only deployed but also latched!
Each of the struts for this tripod, which helps #NASAWebb’s secondary mirror direct light into the instruments, is about 25 feet long (7.6 m)! https://t.co/QTAt5yn8zF #UnfoldTheUniverse pic.twitter.com/UtAMG95c9t
— NASA Webb Telescope (@NASAWebb) January 5, 2022
NASA confirms that the tripod has deployed, but there will be another round of checks before the team moves onto the last major milestone this week: unfolding the primary mirror’s remaining segments. Because Webb had to fold up to fit inside an Ariane 5 rocket, the 6.5-meter (21-foot) mirror has “wings” on the left and right sides that fold back. They’ll have to swing into place before Webb can make any observations.
Webb should be fully deployed in the next few weeks, but it will take months of testing and calibration before we see the first images. Count on that around the middle of the year.