First Layer of Webb’s Sunshield Tightened

Today, at 3:48 pm EST, the Webb team finished tensioning the first layer of the observatory’s sunshield– that is, tightening it into its final, completely taut position. This is the first of five layers that will each be tightened in turn over the next two to three days, until the observatory’s sunshield is fully deployed. The process began around 10 am EST.

This layer is the largest of the five, and the one that will experience the brunt of the heat from the Sun. The tennis-court-sized sunshield helps keep the telescope cold enough to detect the infrared light it was built to observe.

The team has now begun tensioning the second layer.

Webb Team Moving Forward With Sunshield Tensioning

The Webb mission operations team began the first steps in the process of tensioning the first layer of Webb’s sunshield this morning around 10 a.m. EST.

It will take the team two to three days to tension the five-layer sunshield. The plan for today is to focus on the first layer, the largest and the one closest to the Sun.

This critical step in the observatory’s complex sequence of deployments resumed after Webb mission managers paused deployment operations on Saturday to allow for team rest, and then again on Sunday to make adjustments to Webb’s power subsystem and to alter the observatory’s attitude to lower the temperature of the motors that drive the tensioning process.

NASA’s Webb project manager Bill Ochs, Northrop Grumman’s vehicle engineering lead Amy Lo, and NASA’s Webb program director Greg Robinson provided more information about Webb’s first week in space and upcoming deployments in this teleconference held earlier today.

Deployment Timeline Adjusted as Team Focuses on Observatory Operations

Taking advantage of its flexible commissioning schedule, the Webb team has decided to focus today on optimizing Webb’s power systems while learning more about how the observatory behaves in space. As a result, the Webb mission operations team has moved the beginning of sunshield tensioning activities to no earlier than tomorrow, Monday, Jan. 3. This will ensure Webb is in prime condition to begin the next major deployment step in its unfolding process.  

Specifically, the team is analyzing how the power subsystem is operating now that several of the major deployments have been completed. Simultaneously, the deployments team is working to make sure motors that are key to the tensioning process are at the optimal temperatures prior to beginning that operation. 

Using an approach to keep mission operations focused on as few activities as necessary at a time, mission managers have chosen to wait to resume sunshield deployment steps after better understanding the details of how Webb is functioning in its new environment. 

Nothing we can learn from simulations on the ground is as good as analyzing the observatory when it’s up and running,” said Bill Ochs, Webb project manager, based at NASA’s Goddard Space Flight Center. “Now is the time to take the opportunity to learn everything we can about its baseline operations. Then we will take the next steps.”  

Webb’s deployment was designed so that the team could pause deployments if necessary. In this case, Ochs said, they are relying on that flexibility in order to properly address how the massive and complex observatory is responding to the environment of space. 

“We’ve spent 20 years on the ground with Webb, designing, developing, and testing,” said Mike Menzel, of NASA’s Goddard Space Flight Center, Webb’s lead systems engineer. “We’ve had a week to see how the observatory actually behaves in space. It’s not uncommon to learn certain characteristics of your spacecraft once you’re in flight. That’s what we’re doing right now. So far, the major deployments we’ve executed have gone about as smoothly as we could have hoped for. But we want to take our time and understand everything we can about the observatory before moving forward.”  

The timeline for deployments and NASA coverage will be updated as major deployments resume.

 

Webb Sunshield Tensioning To Begin Tomorrow

Work on the deployment of Webb’s sunshield mid-booms went late into the night yesterday. Webb mission management decided this morning to pause deployment activities for today and allow the team to rest and prepare to begin Webb’s sunshield tensioning tomorrow, Sunday, Jan. 2. That deployment is still expected to take place over at least two days.

This will likely affect the full timeline for Webb’s deployment. The timeline will be updated as major deployments resume.

With Webb’s Mid-Booms Extended, Sunshield Takes Shape

With the successful extension of Webb’s second sunshield mid-boom, the observatory has passed another critical deployment milestone. Webb’s sunshield now resembles its full, kite-shaped form in space.

Engineers began to deploy the second (starboard) mid-boom at 6:31 p.m. EST and completed the process at about 10:13 p.m. EST.

The completion of the sunshield cover and mid-boom deployments over the past two days marks a critical milestone for Webb: all 107 membrane release devices associated with the sunshield deployment — every single one of which had to work in order for the sunshield to deploy — have now successfully released. Webb has 178 of these ‘non-explosive actuators’ in all; 107 were used to keep the sunshield safe and folded prior to deployment.

As the mid-booms slowly pushed out horizontally from the spacecraft, each driven by a motor, they pulled the folded membranes of the sunshield with them. This extended the sunshield to its full 47-foot width all the way across the observatory.

“The mid-booms are the sunshield’s workhorse and do the heavy lifting to unfold and pull the membranes into that now-iconic shape,” said Keith Parrish, Webb observatory manager at NASA’s Goddard Space Flight Center.

While the deployments took longer than expected today, that was due to the operations team moving forward with caution and according to the protocols they laid out for dealing with unpredictable situations.

“Today is an example of why we continue to say that we don’t think our deployment schedule might change, but that we expect it to change,” Parrish said. “The team did what we had rehearsed for this kind of situation – stop, assess, and move forward methodically with a plan. We still have a long way to go with this whole deployment process.”

The two mid-boom arms are now locked in their final position. They will hold the sunshield membranes in their proper place, as the team turns to the final stage in the sunshield’s deployment: tensioning.

In the coming days, the team will separate and then individually tension each of the five sunshield layers, stretching them into their final, taut shape. This will create space between the membranes to allow heat to radiate out, making each successive layer of the sunshield cooler than the one below.

Webb’s engineers will begin with the bottom layer – the largest and flattest layer, which is closest to the Sun and will reach the highest temperatures. They will proceed sequentially to the fifth and smallest layer, closest to the primary mirror. Tensioning the layers involves sending commands to activate several motors to reel in a total of 90 cables through numerous pulleys and cable management devices. Sunshield tensioning will take at least two days but may take longer, due to the complexity of the process and the flexibility built into the timeline.

First of Two Sunshield Mid-Booms Deploys

The Webb mission operations team has extended the first of the sunshield’s two “arms” – the port (left side) mid-boom.

The critical step of the port mid-boom deployment was scheduled to begin earlier in the day. However, the team paused work to confirm that the sunshield cover had fully rolled up as the final preparatory step before the mid-boom deployment.

Switches that should have indicated that the cover rolled up did not trigger when they were supposed to. However, secondary and tertiary sources offered confirmation that it had. Temperature data seemed to show that the sunshield cover unrolled to block sunlight from a sensor, and gyroscope sensors indicated motion consistent with the sunshield cover release devices being activated.

After analysis, mission management decided to move forward with the regularly planned deployment sequence. The deployment of the five telescoping segments of the motor-driven mid-boom began around 1:30 p.m. EST, and the arm extended smoothly until it reached full deployment at 4:49 p.m.

As Webb’s deployment steps are all human-controlled, the schedule for deployments could continue to change – as today’s activities showed. Shortly before 6:30 p.m., the team decided to proceed with deploying the starboard mid-boom tonight, and the initial steps of that deployment began at 6:31 p.m.

Editor’s note: This post was updated to reflect the accurate time of the beginning of the starboard mid-boom deployment.

Webb Team Releases Sunshield Covers

Webb’s engineers have released and rolled up the sunshield covers that protected the thin layers of Webb’s sunshield during launch. After the team electrically activated release devices to release the covers, they executed commands to roll the covers up into a holding position, exposing Webb’s sunshield membranes to space for the first time.

The deployment, which took about an hour, concluded at approximately 12:27 p.m. EST.

In their next stages of planned activities, engineers will deploy the sunshield mid-booms, before proceeding with sunshield tensioning. The steps in this process, controlled by humans at Webb’s Mission Operations Center, may change.

Webb’s Aft Momentum Flap Deployed

Shortly after 9 a.m. EST today, the Webb team completed deployment of the observatory’s aft momentum flap. In a process that took about eight minutes, engineers released the flap’s hold-down devices, and a spring brought the flap into its final position.

The aft momentum flap helps minimize the fuel engineers will need to use throughout Webb’s lifetime, by helping to maintain the observatory’s orientation in orbit. As photons of sunlight hit the large sunshield surface, they will exert pressure on the sunshield, and if not properly balanced, this solar pressure would cause rotations of the observatory that must be accommodated by its reaction wheels. The aft momentum flap will sail on the pressure of these photons, balancing the sunshield and keeping the observatory steady.

Just as a ship’s mast must be set in position and the rigging established before the ship unfurls its sails, Webb’s pallet structures, momentum flap, and mid-booms will soon all be in place for Webb’s silver sunshield to unfold. The next steps in Webb’s planned deployment timeline are outlined here.

Webb Ready for Sunshield Deployment and Cooldown

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 NASA’s Goddard Space Flight Center, provided these thoughts:

“The Webb telescope and science instruments are ready to enter the shade, never again to see direct sunlight. One of Webb’s unique design features is using passive cooling by a five-layer sunshield to reach the telescope’s operational temperatures of 45 Kelvin (-380 degrees Fahrenheit). The enormous sunshield is about 70 by 47 feet (21 by 14 meters) when deployed, or approximately the size of a tennis court. The sunshield geometry and size were determined such that the telescope can point within a field of regard that covers 40% of the sky at any time and can observe anywhere in the sky over six months. This innovative architecture enables Webb’s sensitivity to be limited by the natural sky background (mostly zodiacal light) rather than being compromised by thermal glow of the observatory itself, for all wavelengths shorter than 15 microns, for the duration of the mission.

“For launch, the sunshield was folded like a parachute and stowed onto the forward and aft unitized pallet structures (UPSs). Both the telescope and sunshield’s support structures are mechanically connected to each other and the spacecraft bus in order to fit within the Ariane 5’s fairing and withstand the dynamic launch environment.

Deployment Graphic

“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

Webb’s Deployable Tower Assembly Extends in Space

This afternoon, the Webb team successfully extended the observatory’s Deployable Tower Assembly (DTA), creating critical distance between the two halves of the spacecraft.

The DTA extended about 48 inches (1.22 meters), putting room between the upper section of the observatory, which houses the mirrors and scientific instruments, and the spacecraft bus, which holds the electronics and propulsion systems. This creates enough distance to allow the sensitive mirrors and instruments to cool down to the necessary temperatures to detect infrared light. This gap will also provide room for the sunshield membranes to fully unfold.

Engineers perform the final deployment test of the James Webb Space Telescope’s Deployable Tower Assembly in June 2021 at Northrop Grumman Space Park in Redondo Beach, California. Credit: NASA’s Goddard Space Flight Center

The deployment took more than six and a half hours, as engineers activated release devices and configured heaters, software, and electronics, before commanding the DTA itself to extend. The movement of the DTA, which looks like a large, black pipe, is driven by a motor. The team began the deployment at approximately 9:45 a.m. EST and completed it at approximately 4:24 p.m. EST.

This step furthers the team’s progress in deploying Webb’s sunshield – a human-controlled, multi-day process that will continue with the release of aft momentum flap and the sunshield covers.