Original image
Wikimedia Commons

A Brief History of Nuclear Airplanes

Original image
Wikimedia Commons

Airplanes were an integral part of combat during WWII, but flight time was limited by each plane’s fuel capacity—this was a time before mid-flight refueling technology. Planes had to land to refuel fairly frequently making it nearly impossible to fly long distances. One proposed solution for the fuel problem was using atomic energy to power the aircraft.

The Crusader

In 1951, the Atomic Energy Commission ordered the first nuclear-powered airplane into production. The existing B-36 was selected as the base model for the plane, and was modified to carry a reactor and shielding to protect the crew from radiation. The plane’s name was changed to NB-36 to note the nuclear aspect of the plane.

By 1955, the NB-36 (top), christened “The Crusader” by the crew, was able to fly with an operational nuclear reactor on board, though the reactor did not power the plane’s engines. The Crusader and her crew of five flew 47 test flights, mostly over New Mexico and Texas, between 1955 and 1957. The plane’s reactor was operational during 89 of 215 flight hours.

The aim of the test flights was two-fold. First, we wanted to see if nuclear reactors would operate as expected in an airplane (remember, this is early in the Atomic Age), and second, to see if the plane’s shielding would protect the crew from the nuclear reactor’s radiation during flight. This was risky business. In fact, so risky that each test flight was shadowed by a transport plane full of marines. The marines' purpose? To seal off the radioactive crash site should the plane crash. Thankfully, the marines were never needed to seal off a crash site.

The Engines

General Electric HTRE3 and HTRE1 at the Idaho National Laboratory in Arco, Idaho. These are the two remaining direct cycle, nuclear powered airplane engines. Photo courtesy Wikimedia Commons.

Once we knew that nuclear reactors operated as expected in flight and that adequate shielding could be provided to a crew, the U.S. turned its attention to the design of a nuclear engine. Two approaches were taken, by two separate contractors. General Electric set about designing a direct cycle engine, while Pratt & Whitney worked on an indirect cycle engine.

General Electric’s design involved a reactor with longitudinal holes, through which cold air entered the reactor. The cold air then moved into tiny holes, where it was heated by the heat put off by the nuclear reactor during fission. The heated air would then expand and produce thrust, which in theory would power the airplane. The idea is simple in principle, but quite dirty; the direct cycle engine essentially spewed radioactive air all over the place.

Pratt & Whitney’s design was more complex, but safer. The indirect design involved a nuclear reactor and a separate propulsion unit. Molten metal was used to transfer heat from the reactor to the propulsion unit, so there was much less radioactive air in the mix. But the indirect design involved much more plumbing, and so was heavier, which was problematic in an airplane.

Development of both types of engines hummed along steadily, but slowly, until the end of 1958.

Aviation Week

On December 1, 1958, Aviation Week ran an article titled, “Soviets Flight Testing Nuclear Bomber.” The article claimed that the Soviets had flown an atomic-powered plane more than 40 times, with great success. Not to be outdone, the U.S. stepped up their nuclear engine development game.

By 1960, progress was being made with both the direct and indirect cycle engines. The direct cycle engine was running routinely, and test flights looked to be not too far off, but it somehow seemed that Eisenhower was spinning his wheels getting the whole program off the ground. It was a presidential election year. Frustrated that Soviets had an operational atomic airplane before we did, and at Eisenhower’s seeming ambivalence to it, Kennedy promised to pump additional resources into the atomic airplane project should he be elected.

Kennedy won the election—and within several months of taking office, he cancelled the nuclear airplane program all together. What happened? Well, it turns out that Eisenhower’s ambivalence to the whole thing was warranted. Late in his term, he found out that the Soviets did not in fact have an atomic airplane. The whole thing was a hoax. And we bought into it hard.

So, the atomic airplane scheme faded into history. Until the fall of the Iron Curtain.

The 1990s

In the '90s, when the Berlin Wall fell and communism crumbled away, we found out that the Soviets did in fact have an atomic airplane, just not when we thought they did. The Soviets never stopped working on the idea of a nuclear airplane, and during the '60s, they flew an honest- to-goodness atomic powered airplane—forty or so times throughout the decade.

So how did they do it? Shielding the crew from radiation had always been the piece of the puzzle we couldn’t land; in order to provide ample protection to the crew, the shielding would be so heavy that the plane wouldn’t be able to leave the ground. How did the Soviets solve this riddle? They didn’t. The Soviets’ nuclear powered airplane did not provide sufficient shielding to the crew, and the first crew member died three years after the test flights from his exposure to radiation.

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

Original image
Name the Author Based on the Character
May 23, 2017
Original image