Feb 11, 2022
Hear from a Zemax leader about her work on the recently launched James Webb Space Telescope
In honor of International Day of Women and Girls in Science, we checked in with our own Erin Elliott, who spent ten years working on NASA's recently launched James Web Space Telescope before joining Zemax in 2016. She's currently our Principal Research and Development Engineer and Optical Manager for Application Development Engineering. Here's her update on using Zemax OpticStudio for that historic project.
Author: Erin Elliott, Principal R&D Engineer – Optical Manager, Application Development Engineering - Zemax an Ansys Company
Working on the James Webb Space Telescope (JWST) was a formative stage in my aerospace and optical design career. Like many others, I was up at 4:00am last December 25th to witness history. A camera on the upper stage caught the first glint of sunlight reflecting off the deploying solar panel, and that was an epic moment of excitement and pride for me and my former JWST teammates.
Part of that excitement is the same energy that fuels my current everyday projects. Now that I work at Zemax, I have a special appreciation for the hard work and passion our customers put into their various ambitious pursuits, as well as a unique perspective on the software and hardware capabilities they need to be successful. Without Zemax, I couldn't have done what I did for JWST—and without my JWST experience, I wouldn't be as driven as I am to build the software tools that engineers need.
Designing and deploying the world's largest telescope mirror—more than 2.5x the size of Hubble's
The JWST is uniquely characterized by its complex, multi-segmented primary mirror, made up of 18 individual ultra-lightweight beryllium segments coated in gold. The segments unfolded after launch and are currently being aligned to behave as a single mirror that's 6.5 meters across (about 21 feet). This in-space assembly concept is central to the telescope's design, because it allows the collection of much more light than previous instruments of its kind. It also enables the higher levels of resolution and detail that are needed to pursue the JWST mission goals, including observing how stars become planetary systems, measuring the physical and chemical properties of planetary systems, analyzing galaxy formation and evolution, and searching for the first galaxies or luminous objects formed after the Big Bang.
When I worked on JWST, I used Zemax OpticStudio to help design and test the software used for aligning the primary mirror segments, and to design and build hardware for NIRCam, an onboard near-infrared camera that assists with the alignment process.
Figure 1. This illustrates the 4-stage unfolding process of the JWST mirror system, with the fully unfolded telescope at the bottom right. Photo: NASA.
Over two days last month, the ground control crew unfolded the segments and positioned them for final alignment. As of one week ago, the telescope had cooled down sufficiently that the crew turned on NIRCam, which will return images used in the segment alignment process. Now, JWST has begun using our custom wavefront sensing and control (WFSC) software to align and control the individual mirror segments. Once those are in place and all the preliminary tests check out, the telescope will be ready for use by research teams that have been granted time and access by the JWST award selection committee.
Figure 2. Here's a 1/6th scale model of one of the 18 mirror segments, in the optics testbed we used during design and testing of the JWST. Photo: NASA
Looking to the future of aerospace development—and the crucial role that simulation plays
NASA has a mantra: "Test as you fly." In other words, as you design and build something, you should test in the actual flight conditions it will experience, if possible. JWST, though, was too large to test all at once. We had to test it in pieces. As such, software–based simulations were critical for this process; we could model the full system and validate those models using the parts that could be tested. That gave us confidence that the models are giving the right answer for the on-orbit conditions.
For the WFSC software, we built a testbed telescope that was a smaller version of the flight system. We modeled the testbed and the flight system in OpticStudio. We used the models to study and design each step of the WFSC process. Then, we could try out each step in the testbed. The OpticStudio models were also used to translate the testbed results to the flight conditions, and we used the flight models to create statistical predictions for each alignment step, so that we'd know the worst-case and best-case scenarios for the state of the primary during each step of alignment. All of these simulations built confidence that the alignment would proceed as expected on-orbit.
Simulation is only going to increase in importance as aerospace research continues to evolve. As NASA and the rest of us continue to ponder the question "Where are we going next in civilian space?" it quickly becomes clear that the challenges of JWST are just one sign of things to come. Telescopes are going to keep getting larger; we're probably going to need to assemble them in space, rather than on the ground, which means we have to send them up there in multiple pieces; and they're going to flex more, so we'll be increasingly reliant on software like WFSC to keep everything communicating and aligned. By continuing to evolve simulation capabilities in Zemax software, we can keep pace with scientific discovery and the needs of teams like NASA to keep building bigger and better.
Zemax: Doing the hard work to give our customers what they need
Making your way through difficult challenges ultimately clears the path for coming up with new ideas to make future challenges more manageable. My experience on JWST feeds into the ongoing Zemax mission of building next-level optical simulation software. All those rigorous simulation and validation cycles we did for JWST? My job, and Zemax's job, is to make them easier and more accessible to scientists, designers, and engineers.
The OpticStudio STAR Module we released last year is an example of this. At JWST, it was critical to correctly model the thermal and structural loads for the system in zero gravity and at a operational temperature of 40 K. In the industry, this is known as structural, thermal, and optical performance (STOP) analysis. It would have been great to have a software tool that allowed us to easily transfer STOP modeling results into our optical models. Today, the STAR Module does that—it lets optical design teams quickly and easily put structural and thermal deformations into the optics in order to see their impacts on performance.
The best part of my job is getting to talk to customers about what parts of OpticStudio they like to use, and which capabilities they wish we could add. After learning from them as well as firsthand on JWST about the compelling need for STOP analysis, putting the STAR Module into their hands was really satisfying. It was also a leap forward in our mission as a company. We strive to make progress toward those goals every day. It's really an incredible place to work.
Read the full 2017 interview with Erin Elliott on designing the mirror system for the JWST.
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