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Science And Nature

Aligning the Eyes of the Universe Machine

The James Webb Space Telescope, in only a couple of months of operation, has begun to improve our view of the universe. Its imagesmore detailed than that which was possible beforeshow space aglow with galaxies, many of them formed soon following the big bang.

None of the will be possible minus the work of a team led by Scott Acton, the lead wavefront sensing and control scientist for the Webb at Ball Aerospace & Technologies in Colorado. He and his colleagues developedthe systems that align the 18 separate segments of the Webbs primary mirror using its smaller secondary mirror and science instruments. To create clear images in the infrared wavelengths the telescope uses, the segments need to be within tens of nanometers of the form specified in the spacecraft design.

Acton was raised in Wyoming and spent a lot more than 20 years on the Webb team. IEEE Spectrum spoke with Acton after his team had finished aligning the telescopes optics in space. This transcript has been edited for clarity and brevity.

Tell your story. What got you started?

Scott Acton: When I was seven-years-old, my father brought home a fresh television. And he gave me the old television to disassemble. I was just enthralled with what I saw inside this television. And from that moment on I was defined by electronics. You look in a old television and you can find mechanisms, you can find smells and colors and sights and for a seven-year-old kid, it had been just the most beautiful thing Id ever seen.

Fast-forward 25 years and Im employed in the field of adaptive optics. And finally that resulted in wavefront sensing and controls, which resulted in the Webb telescope.

sky with bright stars and gaseous activityCalled the Cosmic Cliffs, Webbs seemingly three-dimensional picture appears like craggy mountains on a moonlit evening. The truth is, it’s the edge of the giant, gaseous cavity within NGC 3324, and the tallest peaks in this image are about 7 light-years high. NASA/ESA/CSA/STScI

Discuss your work obtaining the telescope ready for flight. You done it for a lot more than 20 years.

Acton: Well, we’d to invent all the wavefront sensing and controls. None of this technology really existed in 2001, so we started from the bottom up with concepts and simple experiments. Then more difficult, very complicated experiments and finally something referred to as TRL 6 technologyTechnology Readiness Level 6which demonstrated that people could do that in a flightlike environment. And it had been a question of taking this technology, algorithms, understanding it and implementing it into very robust procedures, documentation, and software, in order that it could then be employed on the flight telescope.

That which was it like finally to launch?

Acton: Well, Ive surely got to say, there is plenty of nervousness, at the very least on my part. I was thinking we’d a 70 percent potential for mission success, or something similar to that. Its like sending your kid off to collegethis instrument that wed been considering and considering.

The Ariane 5 vehicle is indeed reliable. I didnt think there is likely to be any issue with it, but deployment starts, basically, minutes after launch. So, for me personally, the area to be was at some type of computer console [at the area Telescope Science Institute in Baltimore].

And there were lots of things that had to work.

Acton: Yes, right. But there are several things that which are interesting. They will have these exact things called nonexplosive actuators [used to secure the spacecraft during launch]. You can find about 130 of these. And you also actually cant test them. You build them plus they get used, basically, once. Should you choose reuse one, well, its now another actuator as you need to solder it back together. And that means you cant qualify the part, but what that can be done is qualify the procedure.

We’re able to have still had a mission if some didnt fire, but many of them were essential for the success of the mission. So just consider, lets suppose you need to have a 95 percent potential for success. What number raised to the 130th power is add up to 0.95? That number is actually one. These exact things needed to be perfect.

I recall walking home one night, talking on the telephone to my partner, Heidi, and saying, If Im wrong concerning this Ive just completely screwed up the telescope. She said, Scott, thats why youre there. That has been her method of telling me to cowboy up. The duty had ahead right down to somebody and for the reason that moment, it had been me.

I believe the general public perception was that the Webb was in excellent shape and the in-flight setup all went perfectly. Can you say thats accurate?

Acton: In early stages in the mission there have been hiccups, but besides that, Id say things just went beyond our wildest expectations. Section of that boils down to the truth that my team and I had commissioned the telescope 100 times in simulations. And we always managed to get just a little harder. I believe that served us well since when we surely got to the true telescope, it had been quite robust. It just worked.

Take us through the procedure of aligning the telescope.

Acton: The initial image we returned from the telescope was 2 February, in the center of the night. A lot of people had opted home, but I was there, and lots of other folks were too. We just pointed the telescope at the Large Magellanic Cloud, which includes a whole load of stars inside it, and took images on the near-infrared cameras. Individuals were really pleased to see these images since they were looking basically to ensure that the science instruments worked.

However, many folks were really worried about that image, as you could see some very significant astigmatismstronger than we were looking to see from our simulations. Later we’d learn that the telescopes secondary mirror was off in translationabout 1.5 millimeters across the deployment axis and in regards to a millimeter in another axis. And the principal mirror segments were clocked a little from the perfectly aligned state.

Lee Feinberg, the telescope lead at NASA Goddard, texted me and said, Scott, why cant you merely simulate this to see if you will get some images that bad? In order that morning I ran a simulation and could reproduce almost just what we were seeing in these images. We realized that people were not likely to have any major issues with the wavefront.

Describe the cadence of one’s work during commissioning. What would each day end up like?

Acton: Among the rules we create very in early stages was that with regards to wavefront sensing and control, we’d always have two different people near the computers at any moment. Anytime anything significant happened, I usually wanted to ensure that I was there, therefore i got a flat [near the institute in Baltimore]. From my door to the entranceway of the of the Mission Operations Center was a 7-minute walk.

sky with bright star in middle with gasesIn this mosaic image stretching 340 light-years across, Webbs Near-Infrared Camera (NIRCam) displays the Tarantula Nebula star-forming region in a fresh light, including thousands of never-before-seen young stars which were previously shrouded in cosmic dust.NASA/ESA/CSA/STScI/Webb ERO Production Team

There have been certainly times through the process where it had an extremely large pucker factor, in the event that you will. We couldnt point the telescope reliably at the beginning. And lots of our software, for the first steps of commissioning, depended on the immutability of telescope pointing. We wished to have the telescope repeatedly pointed to inside a handful of arc-seconds also it was nearer to 20 or 30. Due to that, a few of the initial moves to align the telescope needed to be calculated, in the event that you will, yourself.

I recall walking home one night, talking on the telephone to my partner, Heidi, and saying, If Im wrong concerning this Ive just completely screwed up the telescope. She said, Scott, thats why youre there. That has been her method of telling me to cowboy up. The duty had ahead right down to somebody and for the reason that moment, it had been me.

However when the result returned, we could start to see the images. We pointed the telescope at a bright isolated star and we’re able to see, individually, 18 spots appearing in the center of our main science detector. I recall a colleague saying, I now believe were likely to completely align the telescope. He felt in his mind’s eye that if we’re able to see through that step, that the rest was downhill.

Youre attempting to patch together the universe. Its hard to obtain it right, and incredibly an easy task to make mistakes. But we achieved it.

Building the Webb was, needless to say, a large, complicated project. Do you consider you can find any particular lessons to be drawn as a result that people later on will dsicover useful?

Acton: Listed below are several really big ones that connect with wavefront sensing and control. One is there are multiple institutions involvedNorthrop Grumman, Ball Aerospace, the Goddard Space Flight Center, the area Telescope Science Instituteand the complication of experiencing each one of these institutional lines. It might have already been very, very hard to navigate. So very in early stages we didn’t have any lines. We were a totally badgeless team. Anybody could speak to anybody. If someone said, No, I believe that is wrong, you need to do it in this manner, even though they didnt necessarily have contractual responsibility, everybody listened.

Another big lesson we learned was concerning the need for the interplay between experimentation and simulation. We built a one-sixth scale model, a completely functional optical style of the telescope, and its own still working. It allowed us, very in early stages, to know that which was likely to be difficult. Then we’re able to address those issues in simulation. That understanding, the interplay between experimentation and modeling and simulations, was essential.

Recognizing needless to say, that its very early, can you yet have a popular image?

Acton: The best image, up to now, was one which was taken over the last real wavefront activity that people did within commissioning. It had been called a thermal slew test. The telescope includes a large sunshield, however the sunshield could be at different angles with regards to the sun. So to be sure it had been stable, we aimed it at a bright star we used as helpful information star, put it in a single orientation, and stayed there for five or six days. And we switched to another orientation for five or six days. It ended up being quite stable. But how will you understand that the telescope wasnt rolling concerning the guide star? To check on this, we took a number of test images with the redundant fine-guidance sensor. Obviously, if you have a 6-1/2 meter telescope at L2 from any competing light sources that’s cooled to 50 kelvins, yes, it really is sensitive. Even just one single 20-minute exposure will probably just have unbelievable detail concerning the deep universe. Imagine what goes on invest the 100 of these images and average them together. We developed a graphic of a few random area of the sky.

james webb telescope image of bright lights against a dark backgroundScott Actons favorite Webb image: A test image of a random portion of the sky, shot with the Webbs fine-guidance sensor. The points with six-pointed diffraction patterns are stars; all the points are galaxies. NASA/CSA/FGS

I sent this image to James Larkin at UCLA, and he viewed it and estimated that that single image had 15,000 galaxies inside it. Each one of those galaxies probably has between 100 [billion] and 200 billion stars.

I dont discuss religion an excessive amount of with regards to this, but I have to have had in my own mind a Biblical mention of the stars singing. I pictured all those galaxies as singing, as though this was a means for the universe expressing joy that in the end these years, we’re able to finally see them. It had been quite an emotional experience for me personally and for many individuals.

You realized that there is so much on the market, and you also werent even really searching for it yet? You’re still phasing the telescope?

Acton: Thats right. I assume I Im uncertain what I expected. I figured youd just see dark sky. Well, there is no dark sky. Dark sky is really a myth. Galaxies are everywhere.

Finally, we surely got to our first diffraction-limited image [with the telescope calibrated for science observations for the initial time]. And thats what sort of telescope is operating now.

Several days later, about 70 folks got togetherastronomers, engineers, along with other team members. An associate of the teamhis name is Anthony Galyerand I had opted halves many years earlier and purchased a bottle of cognac from 1906, the entire year that James Webb was created. We toasted James Webb and the telescope that bears his name.

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