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The Challenges of Building the Hubble Telescope’s Replacement

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NASA

Since 1990, the Hubble telescope has brought us photos that are as beautiful as they are scientifically important. But there’s a limit to what Hubble can see—so space agencies from around the world are collaborating to create a better, more powerful, and literally bigger telescope: the James Webb Space Telescope (JWST), which is projected to launch in 2018. In the SXSW panel “Beyond Hubble: Building NASA’s Next Great Telescope,” scientists and engineers discussed what the Webb telescope will look for and all the engineering challenges that go into actually building the instrument.

What JWST Will Do—And How It Will Do It

According to Alberto Conti, Innovation Scientist at the Space Telescope Science Institute, the Webb telescope is a versatile instrument that has four main goals: To find the first stars, study galaxy evolution, study planet formation, and find habitable planets that might contain water (and, therefore, might also have life). “We build telescopes because they’re time machines,” Conti says. “They tell us about how the universe came to be, and how it works.” Scientists hope that Webb will answer questions like: How did the universe form? Is our solar system unique? Are we alone?

In order to answer these questions, JWST needs to be big—really big. One hundred times more powerful than Hubble, the four-story-tall, infrared optimized telescope will be comprised of 18 hexagonal mirrors that total 21.3 feet in diameter which will allow it to take pictures of faraway worlds, and an 80-foot-long sun shield that will keep the telescope’s eyes cold enough to snap those photos.

While Hubble can capture images of planets the size of Jupiter, JWST will be able to look for planets from the size of Neptune down to the size of Earth, according to Charles Mountain, the director of the Space Science Telescope Institute. And it will do it by looking for infrared spectrums. “On the infrared spectrum, there are three planets that we know a lot about: Venus, Mars, and Earth,” Mountain says. If, using JWST, they can find planets with infrared signatures similar to Earth’s, they might be goldilocks planets—just right to have life. “If we find life, it’ll be as profound as Darwin and Copernicus rolled into one,” Mountain says. “It will bring about a change in our world—we’ll realize we’re not as special that we thought, that evolution happened elsewhere.”

Looking for life begins by looking for stars, because planets that can harbor life will be orbiting around stars. JWST can also use infrared to peer through clouds of gas. “The idea is that we can see thousands of stars embedded in gas clouds because we have the right set of eyes,” Conti says. By looking at the spectra of the disks, Webb will be able to determine what constituents of those disks create planetary systems.

The Engineering Challenges

Building JWST hasn’t been a cakewalk. It has required both creativity and tons of collaboration between scientists, engineers, and companies in the private sector to get it done. Here are the engineering challenges behind key elements of the telescope.

Mirror

In order to see distant objects, JWST needs a big mirror. Blake Marie Bullock, the campaign lead on JWST at Northrup Grumman Corporation, explains the need for a big mirror this way: If you leave a coffee can out overnight in a storm, in the morning, the water in the can will be two inches deep. If you leave out a kiddie pool in the same scenario, the pool will also have water two inches deep—but there will be a lot more water in it. In a telescope, “the same thing is happening with photons,” Bullock says. “If you have a bigger bucket, you can have more photons, and see fainter objects.”

This mirror is so big that it won’t fit in a traditional rocket (Webb will go up in one of the European Space Agency’s Ariane 5 rockets), so engineers had to create a mirror that will fold. “There are 18 hexagons, but three of the hexagons [on each side] are folded down like leaves on a dining room table when it’s stowed,” Bullock says. Once in space, the telescope “unfolds like a flower. Figuring out how this process works takes a lot of engineering.”

Even more complicated is figuring out the prescription. “As you’re manufacturing that mirror on the surface of the Earth, gravity pulls it down and bends that structure,” Bullock says. But when the mirrors are up in space, the gravity is gone—so on Earth, the prescription actually has to be perfectly wrong so that it will be right once the telescope goes into space. As you can imagine, it takes a lot of calculations.

In order to be as precise as the mission requires, JWST’s mirrors have to be very, very smooth. So smooth, Bullock says, that “if you took one of these hexagons and stretched it out to the size of the state of Texas, the biggest bump would be 1 centimeter tall.”

Hot vs. Cold

Infrared is sort of like heat, Bullock says, and because JWST is looking for heat, it doesn’t want to see heat. So engineers are building a five-layer, 80-foot long sun shield that will take photons away from the telescope’s eyes, which much be cold to function. And because there’s such a huge difference in temperature between the hot side of the observatory, where temperatures will reach 185 degrees Fahrenheit, and the cold side, which will be a chilly -388 degrees Fahrenheit, engineers have to think about things like how glue and other materials might behave. Engineers also have to wrestle with how to handle things like the sun shield so that it doesn’t have any creases once it’s deployed.

Weight

The bigger something is, the heavier it is—and the more difficult it is to get it out of Earth’s orbit. JWST is no exception. “As the telescopes get bigger, engineers have to think about how to make it light enough to get into space,” Bullock says. Hubble is just a couple of hundred miles above Earth’s surface, but Webb will be a million miles away, where it is both dark—to make imaging planets and stars easier—and cold (so the telescope functions properly).

Testing

No facility is big enough to test Webb in its entirety, so its components are being tested at Johnson Space Center in Houston, Texas. The facility’s cryogenic chamber, according to Bullock, hasn’t been used since the Apollo missions, so it’s been retrofitted to test JWST’s components. The gold-coated mirrors are being tested six at a time, but the chamber isn’t big enough for the 80-foot sun shield. “That means a lot more math to make sure everything will work the first time,” Bullock says.

Given all of these challenges, how can scientists be sure JWST will work? Nothing is 100 percent, but engineers are working hard to make it happen. “Every piece is tested incrementally, verified, put into a larger system and tested again,” Bullock says. “We’ll spend two years testing it to make sure that it works.”

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iStock // Ekaterina Minaeva
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Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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Scientists Think They Know How Whales Got So Big
May 24, 2017
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It can be difficult to understand how enormous the blue whale—the largest animal to ever exist—really is. The mammal can measure up to 105 feet long, have a tongue that can weigh as much as an elephant, and have a massive, golf cart–sized heart powering a 200-ton frame. But while the blue whale might currently be the Andre the Giant of the sea, it wasn’t always so imposing.

For the majority of the 30 million years that baleen whales (the blue whale is one) have occupied the Earth, the mammals usually topped off at roughly 30 feet in length. It wasn’t until about 3 million years ago that the clade of whales experienced an evolutionary growth spurt, tripling in size. And scientists haven’t had any concrete idea why, Wired reports.

A study published in the journal Proceedings of the Royal Society B might help change that. Researchers examined fossil records and studied phylogenetic models (evolutionary relationships) among baleen whales, and found some evidence that climate change may have been the catalyst for turning the large animals into behemoths.

As the ice ages wore on and oceans were receiving nutrient-rich runoff, the whales encountered an increasing number of krill—the small, shrimp-like creatures that provided a food source—resulting from upwelling waters. The more they ate, the more they grew, and their bodies adapted over time. Their mouths grew larger and their fat stores increased, helping them to fuel longer migrations to additional food-enriched areas. Today blue whales eat up to four tons of krill every day.

If climate change set the ancestors of the blue whale on the path to its enormous size today, the study invites the question of what it might do to them in the future. Changes in ocean currents or temperature could alter the amount of available nutrients to whales, cutting off their food supply. With demand for whale oil in the 1900s having already dented their numbers, scientists are hoping that further shifts in their oceanic ecosystem won’t relegate them to history.

[h/t Wired]

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