Saturdays, for most people at the University of Arizona football stadium, focus on tailgating and touchdowns. But for some, the focus is on making the world’s largest and most advanced mirrors.
The Richard F. Caris Mirror Lab, located on the stadium’s east wing, makes mirrors the size of swimming pools for the biggest telescopes in astronomy.
“There is no other place in the world that does what the mirror lab does,” said Christian Veillet, director of the Large Binocular Telescope. “It makes the biggest ones on the planet.”
The Richard F. Caris Mirror Lab was established in 1980 with its innovative use of the honeycomb shape to build mirrors on the cutting edge of astronomy. World-renowned projects included the Large Binocular Telescope, the Magellan Telescope, the Multiple Mirror Telescope, and the lab is currently working on the Giant Magellan Telescope and the Large Synoptic Survey Telescope.
“There would be no LBT without the Mirror Lab,” Veillet said. “We are like the forerunner for the GMT.”
Built in the early 1990s, the LBT is able to produce an image resolution with two 8.4 meter mirrors that would equal that of a single 23-meter mirror, according to Viellet. It’s much easier for scientists to build smaller mirrors with more accuracy.
“With this technology, we have been able to discover volcanoes erupting on Jupiter’s moon Io,” Veillet said. Before the LBT, images of Io were too blurry to distinguish the landscape.
Because of the high resolution of LBT’s images, astronomers are able to look at things not only in the solar system but far beyond. Veillet said they look at light from galaxies 9 billion light years away. Because light takes time to travel, what they see is an image of a galaxy 9 billion years prior, giving them, and the scientific community at large, insight into the origins of our own galaxy.
LBT is also one of the top telescopes looking for asteroids entering our solar system. If there is a big one headed for Earth, the astronomers at the LBT might be the first ones to see it, according to Veillet.
The mirrors take time and ingenuity to cast, according to Steward Observatory Director Buell Jannuzi. In the late ’60s, astronomers were starting to figure out what worked and what didn’t when it came to building telescope mirrors. UA and the Smithsonian Institute collaborated to make the Multiple Mirror Telescope or MMT on Mount Hopkins south of Tucson, Jannuzi said.
The mirrors for the MMT were salvaged from a failed NASA space telescope. They were made hollow and small because of the weight restrictions that come with sending a telescope into space.
Before then only huge single mirrors were used for Earth-based telescopes. They were hard to make and difficult to transport. What they found using multiple smaller, hollow mirrors was a surprisingly clear image resolution, according to Jannuzi. They came to find hollow mirrors had an advantage for Earth-based telescopes as well; they could heat up and cool down to the temperature around them much faster which meant much less atmospheric distortion. Think about how the air above asphalt becomes distorted on a hot day.
Then, UA astronomy professor Roger Angel, UA astronomer John Hill and others took the idea of multiple hollow mirrors working in tandem and ran with it. The idea of a honeycomb shape was to allow for the lightest and most hollow framework that would still allow for structural support and rigidity.
“He started in the backyard of his house doing some tests with a small oven,” Jannuzi said about Angel. “Eventually we moved to the space in the east wing of the stadium.”
When the lab first started, the group could only cast 3.5-meter mirrors. The key to success, said Jannuzi, was the spin-casting technique. Essentially, the glass is laid out on top of a styrofoam-like mold which is later power-washed out to create the hollow effect, and slowly spun in a giant furnace creating a saucer shape. But with a series of upgrades throughout the 1990s, they were able to successfully cast mirrors as large as 8.4 meters, the size that will be going onto the GMT in 2024.
“Because we’re busy making the GMT mirrors, we’re sending some of the 6.5-meter mirrors over to the College of Optical Sciences,” Jannuzi said. “They’re polishing one mirror for the TAO telescope which is going to Chajnantor, an 18,000-foot-high mountaintop in Chile; they’re also working for the Mexican National Observatory on San Pedro Martir, which is in Baja California.”
In some ways, the casting is the easy part. Buddy Martin, the mirror lab’s lead scientist for polishing and measuring, said it takes about two years after the casting before the mirrors are ready to ship.
“The next stage is called grinding,” Martin said. “The diamond-studded grinder removes glass and is able to get the accuracy of the mirror to one-thousandth of an inch.”
This process takes about a year and doesn’t even scratch the surface of how accurate these mirrors need to be.
The next step, polishing, is where Martin and his team come in.
“It’s wearing the material off at a very slow rate so you can slowly get to an accuracy of one-millionth of an inch,” Martin said. “That’s the bottleneck in this process.”
The polishing team goes through cycles of measuring and making changes in the glass. This is done by programming the polishing tool to make micro adjustments where Martin and his team of engineers see room for improvements, then measuring the accuracy of the glass compared to a computer-generated “perfect mirror.”
The mirrors are measured in a tower at the lab. The measurement tools need to be high above the mirror to detect imperfections in the lightwaves gathered. The polishing team uses a multitude of overlapping tests to ensure no mistakes in measurement were made, something that Martin said can never be ruled out.
To make the process even more difficult, scientists and engineers working on the mirror need to account for every movement of the mirror — from taking it from the lab to the testing tower, all the way to the intercontinental flight destination of the telescope.
“With something that large, you can never assume that it will hold its shape,” Martin said.
Still, with laser measurement tools, Martin is able to detect irregularities at one-fifth of one-millionth of an inch.
“We are pushing the limits of the knowledge we have and the work we’ve done, or that anyone has ever done,” Martin said.
To give some perspective on the accuracy of the mirrors, If you took an 8.4-meter mirror made at the Richard F. Caris mirror lab and scaled it up 1 million times, it would be about the size of North America, according to Martin. He said the largest bump in the mirror would only be an inch high and the deepest valley would be an inch low.
“The LBT, as well as the MMT, were pioneers in adaptive optics,” Jannuzi said. “There’s blurring that’s caused by your telescope jittering or heat near your mirror, but there is also all sorts of disturbance in the atmosphere, so they’re able to take that out by changing the shape of the mirror.”
In the reference body, or structural support, of the mirror there are magnets. Astronomers wanting to adjust for a blurred image can adjust the magnetic resonance in the mirror which makes small changes to the shape of the mirror, correcting for any blur.
In the ’90s, Jannuzi said, three main types of mirrors were implemented. All three worked, but the large and thin meniscus mirrors were very fragile and hard to make, and smaller segmented mirrors took a lot of time to produce. Mirrors made at the Richard F. Caris Mirror Lab may take a long time to produce, but they are sturdier and telescopes usually only need one or two of them. At the moment, the Richard F. Caris Mirror Lab is the only one making mirrors for large Earth-based telescopes in the world, according to Jannuzi.
The only other competitor in the race for the best images of space are space-based telescopes. Space telescopes have a particular advantage over Earth-based because there is no atmosphere to distort the image. But Jannuzi isn’t worried about the mirror lab losing any business.
“It’s always cheaper to build a really big telescope on Earth than it is to send one into space,” Jannuzi said.
For example, NASA’s successor to the Hubble Telescope, the James Webb Space Telescope, set to launch in 2021, will cost about $10 billion. The James Web Telescope’s segmented mirror, made by NASA, will be 6.5 meters across. Meanwhile, the GMT, featuring UA’s 8.4-meter mirrors, will have 10 times the resolution power as Hubble and will only cost $1.3 billion to make, according to Jannuzi.
As of now, the mirror lab has cast five 8.4-meter mirror segments for the GMT, to be completed in 2024. The first segment is finished polishing and the second is close behind. They are also casting several 6.5-meter segments for the Mexican government and the University of Tokyo.
“6.5-meter segments are a good size for people who need mirrors for cheap,” Jannuzi said. Having a higher number of smaller mirrors in production is good for astronomy, according to Jannuzi, because there is an infinite amount of space and only so many eyes looking at it.
Jannuzi said the state has provided the mirror lab with funding for salaries and operations, but the majority of the mirror lab’s funding comes from grants and donations, such as $20 million in gifts from Richard F. Caris in 2015.
Caris was the owner of Interface Inc., which makes electrical components for UA mirrors. His financial impact on UA’s contribution to the GMT led to the renaming of the mirror lab. The lab is also supported by contracts like that with the Mexican government and the University of Tokyo, to build mirrors which cost from $15 million to $25 million depending on the size, according to Jannuzi.
While Jannuzi admitted the mirror lab doesn’t make any profit for the state, the university or themselves, the success of the mirror lab is reflected in all the discoveries, data and innovations made by the astronomers using UA mirrors.
Chandler Donald is a reporter for the Arizona Sonora News, a service from the School of Journalism with the University of Arizona. Contact him at [email protected].
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