He’s a metrologist Yeah, I’m a metrologist.

Welcome back to Smarter Every Day. I have been trying to interview my own father for two years now, as he has a really unique job. We are here at his work, and everything about this is weird. It’s 2 a.m., and we are here to see what he does.

My dad worked for the auto industry when I was growing up, and he’s something called a metrologist. He would make new, interesting ways to measure parts as they came off the assembly line.

So here’s the deal. I got to investigate the James Webb Space Telescope in a couple of really interesting ways. I got to speak to Dr. James Mather, the chief scientist over the whole project. And I also got to speak to my dad, who had been working on the sunshield of the telescope for many years.

The sunshield protects the optics of the telescope from heat and light from the sun, and reflected heat and light from the earth and the moon. There are five layers to the sunshield, and they unfolded like origami ten days after launch.

Now, I’m excited to go back in time to 2016 when I got to go into the clean room with my dad as he’s working to measure the sun shield for the James Webb Space Telescope. I didn’t understand all of it, so I got to just ask questions. This is amazing for me because it’s dad and it’s me getting to ask him stuff.

So here we are, ready to learn about the sun shield for the James Webb Space Telescope with Darrell Sandlin. All right, so what’s the deal? We are on the magical clean side now. Positive pressure from there to here to the- So all dust is blowing that way. This is Bobby Thorn, a metrologist. We’ve got a measurement crew! And then you had something else that was like a little tripod with a camera on it.

-Yes.Combined, it’s almost a century I’ve known you for 25 years, and you’re the specialist on the sunshield for the James Webb Space Telescope. I’ve done process, measurements, and even got a patent on one of the things we’ve done. It was a big moment for me to walk into the cleanroom and be standing in the same room with this thing and my dad. I had to do a lot of email to get in here! So I want to do what you used to do when I was a kid and you’d teach me stuff, but 20 years later and with my engineering degree. Can you do that? Sure! So let’s go have fun and learn about how the sunshield keeps the telescope shielded from the sunlight, Earth light, and moonlight. It’s one-thousandth of an inch thick and has five layers. You mount pully blocks very precisely within five-thousandths of an inch and when you put different weights on them, the structures will flex and bend a little bit. You’re a metrologist, measuring stuff, and you used to measure car parts. When you retired, you worked for the Air Force, Navy, Army, and medical things like knee and hip joints. Now you’re measuring the sunshield and I saw you had two types of measurement devices - a laser scanner and a tripod with a camera. it takes a slice of the surface and then it moves on to the next slice and it keeps doing that until it’s done.Exactly.And then it’ll take all those points and put it into a 3D model. We’re using two different types of instruments in this project: a laser scanner and a laser tracker. The laser scanner paints a wide area with a laser to give us a point cloud of the room, while the laser tracker is used to precisely measure individual points with a high degree of accuracy.

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Alright, so this is the tracker right Mark? Yes, this is the laser tracker. We’ve got four monuments. We’ve got holes drilled in the floor for solid points. What they’ll do is determine a frame of reference relative to the structure and the rim, the pulley block points which allows us to take tracker measurements from different spots. So what we’ve already done is we bumped into the floor. We measured for monuments. Now we have a frame of reference. The frame is actually about a foot underneath the floor right now. So basically the tracker knows where it’s at. Yes. It’s locating the instrument. So we’ve located the instrument. It knows where it is compared to everything else. It does all of the transformations and that way we can point at things, it makes life a lot more convenient. We’ve got a measurement script that says go here, go there, go there. So when Bobby and Darrell are running around in the middle of the night, making measurements, I’ll call out where we’re measuring. They’ll make measurements, and- Can we simulate a measurement now? -Yes. All right. For instance, you’ve got our alignment for that sphere over there. That is sphere number three. We got one, two, three. We just go clockwise around the membrane Five and seven and eight are in the rim So I’ll point at that one, we’ll do a simulated measurement for S3. Okay, sounds good. I’ll do point test three, and you’ll see the tracker swing around. We’ve got it docked in the center of that sphere now. So this is your retroreflector, this is a corner reflector? This is a corner reflector. And I can tell that because anywhere I move the camera I can see the camera lens in the corner reflector. Right -Alright, cool. So you’re going to…how do you locate that sphere? Well, the detector knows where the center is supposed to be. We’ll take this will measure up to seven points around it to get the actual position of it. Okay. So you just bump the side of that sphere up next to that sphere. I touch it, but he’ll point to it and he’ll say I’ll fire the beam for you, which is what I’ll do right now the laser tracker will turn green when I do this. Alright. When I intercept the beam I’ll intercept the beam now. Alright, I have the beam. Okay so I can see it in the corner reflector now. So…So you can carry the beam with you? -Yeah. Now I can touch the side of it and it knows that I’m touching it. I’ll move it a little bit and then the software will say “Waiting for stable, Waiting for measurement” It wait till it gets quite a few measurements that are stable, not moving, and it’ll acquire one point, then I’ll move it when it stabilizes, it’ll acquire a second point. I do the seven times. Four, five, six, seven. What I try to do is go to the North Pole go around the [?] hemisphere and then take an equator so they get a good hemisphere. It takes seven points and calculates the exact center of the sphere. But if you had, if you had all of the points around the perimeter of it, you wouldn’t be able to get depth in as high of a tolerance. Right, It’s a three-dimensional surface. You know, it’s a 6.9-inch sphere, all of them about the same size. So it’s important to define as wide of a position as possible. It’s just a circle. Not a plane but the three dimensional center of the sphere. Got it. That’s what the laser scanner, this center, all these spheres here, each point will be compared to the scan and that lets us position the scan relative to…So it’s a temporary datum -Right. The most important and accurate data comes from laser scanners, which measure the position of points within less than 0.003 inches. This is very tight when measuring a large plastic surface. The scanner does not actually register to the coordinate frame, but is instead a temporary reference for the scanner to get back to the coordinates frame for the rest of the system. Laser scanners work by shooting photons from one emitter to an object and then getting a reflection back to a detector. Knowing the speed of light in air and the time it takes for the light to go out and back, one can use algebra to figure out the distance of the object. Knowing the direction in both azimuth and elevation, one can use trigonometry to calculate the 3D coordinate of the object. To get the most accurate readings, the laser scanner should be as orthogonal to the object as possible, meaning as close to 90 degrees as possible. To ensure this, laser targets are used, which are made of flash breaker tape and are precisely located with a laser tracker. The laser scanner can pick up on diffuse reflection much better than the highly reflective strip, allowing it to tell where the surface is. A 3D model of the shield is used to render the surfaces and label the features. So Naveen will process the data, and the final data product is a plot of the shape of the membrane in its corrugate frame. He will compare the data to a finite element analysis of it and put it under a 3x load to measure the shape of the membrane in a weightless environment. It’s like, you know, a very slow, calculated motion.

Naveen was the smart guy that Dad and the team would take the data to. When they measured with lasers, they would get a huge amount of data which Naveen would then use to do coordinate transformations and add all the scans up, comparing it to a model to see which spots were high and which spots were low. Naveen was not only a Ph.D. in nuclear fusion, but also an officer of the von Braun Astronomical Society, and had a passion for astronomy. When measuring the kapton, they had to sneak through the room due to air movement and do the testing in the middle of the night to avoid disturbance from outside. When in the clean room, only one or two persons would be allowed to go in and walk very slowly to change the scanning locations, assuming a position of calculated motion. So the catenary curve is the curve that is created by the tension of the two forces from the pulleys.Got it.Thank you for the explanation. It’s been quite a journey for Bobby and I working on this assembly table. We can lay on our bellies and use the gantry to reach about ten feet in board. The laser tracker helps us pinpoint precise points and mark them, then technicians come in and punch holes or adhere parts. We use Pro/E design software to flatten the curved structure and Northrop Grumman gives us the recipe of where the holes go. We measure twice and cut once to make sure the punches are in the right spot and have other people look at our work. We have been working on this for the past six years and the last two years have been devoted to the flight material which will actually see space. Bobby and I have put all the structure in place and it’s been tiring work, but Bobby is eager to see it fly! It’s a beautiful sight.

That’s awesome. So, Bobby has been putting in a lot of effort to help the sissy man pull his weight. It’s called thermal bonding, and the company that owns the process to create the sunshield is called Mantech NeXolve. Bobby has put a corner reflector to simulate the telescope, and he has worked hard to make the surface flat within 0.005". It took two and a half days to get it that flat, and shims were used to help with the process. After all the hard work, Dad and Bobby took a selfie in the spot where the telescope is going to be. Then, the team folded up the sunshield to ship it out to California. It was a beautiful and complex origami dance of sorts, representing the whole James Webb Space Telescope program - a technological collaboration of a lot of people working together to accomplish something extraordinary. Finally, the launch was a success, and the sunshield punched a hole through the clouds. Yeah, that’s what’s happening right now. I never imagined I would come to the United States and get to work on a telescope like this, which is now in space. It’s extraordinary what ordinary people can do - like my dad and the thousands of people from all over the world who came together to make this dream a reality. I commissioned an artist to make a shirt for the James Webb Space Telescope with all the science on it. If you want one, I’ll leave a link in the description. Alright, so what are we doing now? You’ve got to go to the bathroom before you go in? Tell you what, it’s always a good idea to go to the bathroom if you have to.