Webb Mirror Segment Deployments Complete

Last week, the Webb team began moving the observatory’s individual mirror segments out of their launch positions. Today, we hear from Erin Wolf, Webb program manager at Ball Aerospace, about the completion of that process:

“Today, the James Webb Space Telescope team completed the mirror segment deployments. As part of this effort, the motors made over a million revolutions this week, controlled through 20 cryogenic electronics boxes on the telescope. The mirror deployment team incrementally moved all 132 actuators located on the back of the primary mirror segments and secondary mirror. The primary mirror segments were driven 12.5 millimeters away from the telescope structure. Using six motors that deploy each segment approximately half the length of a paper clip, these actuators clear the mirrors from their launch restraints and give each segment enough space to later be adjusted in other directions to the optical starting position for the upcoming wavefront alignment process. The 18 radius of curvature (ROC) actuators were moved from their launch position as well. Even against beryllium’s strength, which is six times greater than that of steel, these ROC actuators individually shape the curvature of each mirror segment to set the initial parabolic shape of the primary mirror.

“Next up in the wavefront process, we will be moving mirrors in the micron and nanometer ranges to reach the final optical positions for an aligned telescope. The process of telescope alignment will take approximately three months.”

—Erin Wolf, James Webb Space Telescope Program Manager, Ball Aerospace

Mirror, Mirror…On Its Way!

With major deployments complete, Webb continues its journey to its final halo orbit around L2. In the meantime, there are several smaller deployments in the next couple of weeks, which constitute the beginning of a several-month phase of aligning the telescope’s optics. This week, we have started the process of moving the mirror segments (all primary plus secondary) out of their stowed launch positions. For more details, here is Marshall Perrin from the Space Telescope Science Institute, home of the Webb Mission Operations Center:

“To support the movable mirrors during the ride to space, each of them has on its back three rigid metal pegs which can nestle into matching holder sockets in the telescope structure. Before launch, the mirrors were all positioned with the pegs held snug in the sockets, providing extra support. (Imagine Webb holding its mirrors tucked up close to its telescope structure, keeping them extra safe during the vibrations and accelerations of launch.) Each mirror now needs to be deployed out by 12.5 millimeters (about half an inch) to get the pegs clear from the sockets. This will give the mirrors ‘room to roam’ and let them be readied in their starting positions for alignment.

“Getting there is going to take some patience: The computer-controlled mirror actuators are designed for extremely small motions measured in nanometers. Each of the mirrors can be moved with incredibly fine precision, with adjustments as small as 10 nanometers (or about 1/10,000th of the width of a human hair). Now we’re using those same actuators instead to move over a centimeter. So these initial deployments are by far the largest moves Webb’s mirror actuators will ever make in space.

“And we don’t do them all at once. The mirror control system is designed to operate only one actuator at a time. That way is both simpler (in terms of the complexity of the control electronics) and safer (since computers and sensors can closely monitor each individual actuator as it works). Furthermore, to limit the amount of heat put into Webb’s very cold mirrors from the actuator motors, each actuator can only be operated for a short period at a time. Thus, those big 12.5-millimeter moves for each segment are split up into many, many short moves that happen one actuator at a time. Scripts sent from the Mission Operations Center will direct this process under human supervision, slowly and steadily moving one actuator at a time, taking turns between segments. At full speed, it takes about a day to move all the segments by just 1 millimeter. It’s about the same speed at which grass grows!

“This may not be the most exciting period of Webb’s commissioning, but that’s OK. We can take the time. During the days that we’re slowly deploying the mirrors, those mirrors are also continuing to slowly cool off as they radiate heat away into the cold of space. The instruments are cooling, too, in a gradual and carefully controlled manner, and Webb is also continuing to gently coast outwards toward L2. Slow and steady does it, for all these gradual processes that get us every day a little bit closer to our ultimate goal of mirror alignment.”

—Marshall Perrin, deputy telescope scientist, Space Telescope Science Institute

Webb Begins Its Months-Long Mirror Alignment

Webb has begun the detailed process of fine-tuning its individual optics into one huge, precise telescope.

Engineers first commanded actuators – 126 devices that will move and shape the primary mirror segments, and six devices that will position the secondary mirror – to verify that all are working as expected after launch. The team also commanded actuators that guide Webb’s fine steering mirror to make minor movements, confirming they are working as expected. The fine steering mirror is critical to the process of image stabilization.

Ground teams have now begun instructing the primary mirror segments and secondary mirror to move from their stowed-for-launch configuration, off of snubbers that kept them snug and safe from rattling from vibration. These movements will take at least ten days, after which engineers can begin the three-month process of aligning the segments to perform as a single mirror.

Following the Next Steps in Webb’s Journey

After two weeks of complex structural deployments, Webb has passed a major milestone and is now fully unfolded in space. For insight on what to expect in the months ahead and how to follow along, we hear from Alexandra Lockwood, project scientist for Webb science communications at the Space Telescope Science Institute:

“Words can’t describe the pride and excitement the Webb team is feeling right now. From engineers to scientists to IT staff to graphic designers to administrative personnel (and more!), we are all overjoyed with the incredible successes of the observatory to date. While we still have a long way to go before getting the science, the engineering feats that have been accomplished, on Earth and now in space, are awe-inspiring. They are a testament to the hard work and expertise of the international Webb team.

“Now that the action-packed deployment sequence is over, we are moving into a much slower, yet deliberate, phase of the commissioning process. In the next two weeks, we will move each of the 18 primary mirror segments, and the secondary mirror, out of their launch positions. Then five months of commissioning will include 1) further cooling of the entire observatory, and of the Mid-Infrared Instrument in particular, 2) checking and then aligning the secondary and 18 mirror segments into a single coherent optical system, first with the NIRCam instrument and then with all instruments individually and in parallel, and 3) calibrating of each of the four instruments and their many scientific modes. The novelty and variety of science that this observatory can produce requires thousands of things to be checked ahead of time. But rest assured that this summer will sizzle with the hot (nay cold?) observations we will soon be sharing!

“The team is committed to keeping you informed – even through the often slow and meticulous parts of this commissioning process. This blog will be updated weekly, and sometimes more often. Please check back to hear more status updates, in-depth explanations of Webb’s science and technology, and even some fun team anecdotes!

“We’re excited to be on this journey to #UnfoldTheUniverse with you.”

—Alexandra Lockwood, project scientist for Webb science communications, Space Telescope Science Institute

Primary Mirror Wings Deployed, All Major Deployments Complete

Today, at 1:17 p.m. EST, NASA’s James Webb Space Telescope completed all of its large-scale deployments with the extension and latching of its starboard primary mirror wing. Now that the telescope is structurally fully deployed – with the secondary mirror tripod and both primary mirror wings in place – the three-month process of aligning all of Webb’s telescope optics into a precise system can now commence. Learn more.

Starboard Primary Mirror Wing Deployment Underway

The Webb mission operations team has given the ‘go-ahead’ to move forward with the extension of its starboard primary mirror panel. This is the last of the major deployments on the observatory, and its completion will set the stage for the remaining five and a half months of commissioning, which consist of settling into stable operating temperature, aligning the mirrors, and calibrating the science instruments.

Live coverage of the deployment, from the Webb Mission Operations Center at the Space Telescope Science Institute in Baltimore, will stream on nasa.gov/live starting no earlier than 9 a.m. EST.

First of Two Primary Mirror Wings Unfolds

Webb’s iconic primary mirror is taking its final shape. Today, the first of two primary mirror wings, or side panels, was deployed and latched successfully. Each side panel holds three primary mirror segments that were engineered to fold back to reduce Webb’s overall profile for flight.

The process of deploying the port side mirror wing began at approximately 8:36 a.m. EST. At approximately 2:11 p.m. EST, engineers confirmed that the panel was fully secured and locked into place, and the deployment was complete.

Now that the port side wing panel is locked in place, ground teams will prepare to deploy and latch the starboard (right side) panel tomorrow. Upon completion, Webb will have concluded its major deployment sequence.

Learn more about Webb’s deployment timeline online.

Primary Mirror Deployment Has Begun

Engineers have begun the final stage of Webb’s major structural deployments: the unfolding of its two primary mirror wings. These side panels, which were folded back for launch, each hold three of the observatory’s 18 hexagonal, gold-coated mirror segments.

The team is beginning today with the mirror wing on the port (left) side of the observatory. Engineers must first release mechanisms that held the wing in place for launch, in order to allow the wing to deploy. The panel then rotates into position, a motor-driven process that takes about five minutes. Once the wing is extended, engineers begin a meticulous, two-hour process to securely latch it into place.

The deployment of the second primary mirror wing, planned for tomorrow, will follow the same process.

Why Doesn’t Webb Have Deployment Cameras?

As NASA’s James Webb Space Telescope makes its way out to its intended orbit, ground teams monitor its vitals using a comprehensive set of sensors located throughout the entire spacecraft. Mechanical, thermal, and electrical sensors provide a wide array of critical information on the current state and performance of Webb while it is in space.

A system of surveillance cameras to watch deployments was considered for inclusion in Webb’s toolkit of diagnostics and was studied in-depth during Webb’s design phase, but ultimately this was rejected.

“Adding cameras to watch an unprecedently complicated deployment of such a precious spacecraft as Webb sounds like a no-brainer, but in Webb’s case, there’s much more to it than meets the eye,” said Paul Geithner, deputy project manager – technical for the Webb telescope at NASA’s Goddard Space Flight Center. “It’s not as straightforward as adding a doorbell cam or even a rocket cam.”

First of all, Webb is big, undergoes many configuration changes during deployment, and has many specific locations of import to deployment. Monitoring Webb’s deployments with cameras would require either multiple narrow-field cameras, adding significant complexity, or a few wide-field cameras that would yield little in the way of helpful detailed information. Wiring harnesses for cameras would have to cross moving interfaces around the observatory and add more risk of vibrations and heat leaking through, presenting a particular challenge for cameras located on the cold side of Webb.

Then there’s the issue of lighting. Webb is very shiny, so visible cameras on the Sun-facing side would be subject to extreme glare and contrast issues, while ones on the cold, shaded side would need added lighting. Although infrared or thermal-imaging cameras on the cold side could obviate the need for illumination, they would still present the same harnessing disadvantages. Furthermore, cameras on the cold side would have to work at very cold cryogenic temperatures. This would either require ‘ordinary’ cameras to be encapsulated or insulated so they would work in extreme cold, or development of special-purpose cryogenic-compatible cameras just for deployment surveillance.

Notwithstanding these challenges, engineers mocked up and tested some camera schemes on full-scale mockups of Webb hardware. However, they found that deployment surveillance cameras would not add significant information of value for engineering teams commanding the spacecraft from the ground.

“Webb’s built-in sense of ‘touch’ (for example, switches and various mechanical, electrical, and temperature sensors) provides much more useful information than mere surveillance cameras can,” said Geithner. “We instrumented Webb like we do many other one-of-a-kind spacecraft, to provide all the specific information necessary to inform engineers on Earth about the observatory’s health and status during all activities.” Engineers can also correlate years of data from ground testing with telemetry data from flight sensors to insightfully interpret and understand flight sensor data.


By Thaddeus Cesari, Webb science writer, NASA’s Goddard Space Flight Center, Greenbelt, Md.

Webb’s Specialized Heat Radiator Deployed Successfully

At about 8:48 a.m. EST, a specialized radiator assembly necessary for Webb’s science instruments to reach their required low and stable operating temperatures deployed successfully. The Aft Deployable Instrument Radiator, or ADIR, is a large, rectangular, 4 by 8-foot panel, consisting of high-purity aluminum subpanels covered in painted honeycomb cells to create an ultra-black surface. The ADIR, which swings away from the backside of the telescope like a trap door on hinges, is connected to the instruments via flexible straps made of high-purity aluminum foil. The radiator draws heat out of the instruments and dumps it overboard to the extreme cold background of deep space.

The deployment of the ADIR – a process that released a lock to allow the panel to spring into position – took about 15 minutes.

Webb’s final series of major deployments is planned to start tomorrow, Jan. 7, with the rotation into position of the first of two primary mirror wings. The second primary mirror wing – Webb’s final major spacecraft deployment – is planned for Saturday, Jan. 8.