James Webb Space Telescope 29 December, 2021 Update - Sunshield Deployment Started and Excess Fuel

Engineers at Northrop Grumman Space Park in Redondo Beach, California, oversee Webb’s final mirror fold test in April 2021. The forward pallet structure is seen here in the foreground, in its unfolded state. Credit: Northrop Grumman.

As the James Webb Space Telescope continues its voyage to L2, the news from NASA is all good.

NASA reported yesterday that the forward pallet structure was lowered beginning a multi-day sunshield deployment.

"The Webb mission operations team concluded the deployment of the first of two structures that hold within them Webb's most unpredictable and in many ways complicated component: the sunshield."

"The structures - called the Forward and Aft Unitized Pallet Structures - contain the five carefully folded sunshield membranes, plus the cables, pulleys, and release mechanisms that make up Webb's sunshield. The team completed the deployment of the forward pallet at approximately 1:21 p.m. EST, after beginning the entire process about four hours earlier. The team will now move on to the aft pallet deployment."

"The deployment of the forward pallet required several hours of the mission operations team carefully walking through dozens of steps - only one of which was the actual motor-driven deployment to move the pallet from its stowed position to its deployed state. The lowering of the forward pallet also marks the first time that structure has conducted that movement since it underwent its final unfolding and deployment test in December 2020 at Northrop Grumman Space Park in Redondo Beach, California."

"The deployment of the pallet structures begins what will be at least five more days of necessary steps to deploy the sunshield - a process that will ultimately determine the mission's ability to succeed. If the sunshield isn't in place to keep Webb's telescope and instruments extremely cold, Webb would be unable to observe the universe in the way it was designed."

"The steps involved - outlined here - will continue after today with the extension of the Deployable Tower Assembly, followed by the release of the sunshield covers, the extension of the mid-booms, and finally the tensioning of the five Kapton layers of the sunshield itself."

"As the deployment of the sunshield will be one of the most challenging spacecraft deployments NASA has ever attempted, the mission operations team built flexibility into the planned timeline, so that the schedule and even sequence of the next steps could change in the coming days."

NASA then reported that the Aft Sunshield Pallet had deployed.

Mission Lifetime Likely Extended

"After a successful launch of NASA's James Webb Space Telescope Dec. 25, and completion of two mid-course correction maneuvers, the Webb team has analyzed its initial trajectory and determined the observatory should have enough propellant to allow support of science operations in orbit for significantly more than a 10-year science lifetime. (The minimum baseline for the mission is five years.)"

"The analysis shows that less propellant than originally planned for is needed to correct Webb's trajectory toward its final orbit around the second Lagrange point known as L2, a point of gravitational balance on the far side of Earth away from the Sun. Consequently, Webb will have much more than the baseline estimate of propellent - though many factors could ultimately affect Webb's duration of operation."

"Webb has rocket propellant onboard not only for midcourse correction and insertion into orbit around L2, but also for three necessary functions during the life of the mission: "station keeping" maneuvers - small thruster burns to adjust Webb's orbit; pointing the telescope toward science targets; and what's known as momentum management, which maintains Webb's orientation in space."

"The extra propellant is largely due to the precision of the Arianespace Ariane 5 launch, which exceeded the requirements needed to put Webb on the right path, as well as the precision of the first mid-course correction maneuver - a relatively small, 65-minute burn after launch that added approximately 45 mph (20 meters/sec) to the observatory's speed. A second correction maneuver occurred on Dec. 27, adding around 6.3 mph (2.8 meters/sec) to the speed."

"The accuracy of the launch trajectory had another result: the timing of the solar array deployment. That deployment was executed automatically after separation from the Ariane 5 based on a stored command to deploy either when Webb reached a certain attitude toward the Sun ideal for capturing sunlight to power the observatory - or automatically at 33 minutes after launch. Because Webb was already in the correct attitude after separation from the Ariane 5 second stage, the solar array was able to deploy about a minute and a half after separation, approximately 29 minutes after launch."

This last item is noteworthy. Shortly after the launch some had wondered why the solar array had deployed so early. Now we have our answer.

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