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It Came From Space! Man-Made Objects That Crashed Back to Earth

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Most orbital debris is in low Earth orbit, where "what goes up must come down" — derelict satellites, spent rocket boosters, explosive bolt shrapnel, payload fairings, interstage structures, payload adapters, spin-up counterweights, and more. Most reentering debris is small and burns up on reentry. But some of it is large and survives reentry. Occasionally, people even find it. To date, no one is known to have been injured, and, statistically speaking, debris is most likely to fall over water. But it's really only a matter of time before someone does get hurt.

Here is a look at some of the more interesting man-made objects that have fallen from space.

Cosmos 954

The Soviet Union fielded an assortment of radar ocean reconnaissance spacecraft (RORSATs) powered not by solar arrays but by actual honest-to-gosh nuclear reactors. They were designed to eject their nuclear cores to a high, disposal orbit at the end of their lifetimes, but on at least one occasion, this did not happen. Cosmos 954's core was still on board when it reentered the atmosphere on January 24, 1978. Although another RORSAT with a similar predicament had wound up safely in the ocean, this one wasn't so lucky; highly radioactive debris was scattered across the Northwest Territories, Alberta, and Saskatchewan, Canada, on a 600 km path. The Soviets refused to acknowledge that any material had survived reentry until a joint US/Canadian recovery mission cleaned up the debris and billed the USSR more than six million Canadian dollars. (The USSR ultimately paid about half of that.) Most of the spacecraft's mass remained unaccounted for, however. This is a bit concerning since, of the 1% of fuel that was recovered, one fragment was so radioactive that a person holding it for a moment would receive a lethal dose.

Members of Operation Morning Light, wearing snowshoes and winter survival gear, use Geiger counters to locate debris.


The most famous piece of space debris ever, this 69,000 kg space station had been built from an unused S-IVB upper stage from a Saturn V, and boosted into orbit by another Saturn V. Today, it holds the record for the third largest space station after the ISS and Mir. After consuming most of the remaining Apollo hardware, the station was abandoned, with the plan of sending the new Space Shuttle up to reboost it and periodically visit. The Sun had other ideas; solar activity puffed out the Earth's atmosphere, increasing drag, and Skylab fell from orbit largely uncontrolled on July 11, 1979. With the media and diplomatic channels awakened by the Cosmos 954 reentry, there was intense interest. NASA predicted 1 in 152 odds of striking a person. There was still some control over the spacecraft, so NASA attempted to control the reentry by adjusting the station's altitude. This worked, but the station took longer to burn than expected, and there was a 4% error in the calculation — it ended up hitting Australia, strewing debris across Western Australia southeast of Perth. It was the most massive object ever to reenter uncontrolled, tipping the scales at 85 tons. (The Mir space station was more massive, but made a controlled entry over the South Pacific.)

Fragment of Skylab, recovered from the crash site and displayed at the US Space and Rocket Center

Salyut 7

In the 1970s, the Soviet Union launched a series of space stations under the designation "Salyut." All of these heavy spacecraft eventually reentered, but the last of them (and the heaviest) was Salyut 7. Equipped with two docking ports to permit resupply and crew exchange, Salyut 7 had enjoyed a strong career starting in 1982. Near the end of its lifespan, an unmanned TKS spacecraft designated Cosmos 1686 arrived and docked to the station, expanding its pressurized volume and demonstrating the concept of modular stations in preparation for the launch of Mir the following year. In 1986, the first Mir crew made a brief trip to Salyut 7, the last to visit the station. It was then abandoned. On February 7, 1991, the station finally fell from orbit, reentering over Argentina and scattering debris near the town of Capitan Bermudez. With the TKS module attached, the combined system had a mass of 40,000 kg. Unlike its Salyut predecessors, its reentry was completely uncontrolled. More about the Salyut 7 debris, including the scientific analysis of a tank recovered from the crash site, is available here.

Delta II Upper Stage

Many upper stages have reentered through the years; in fact, rocket boosters constitute the majority of large space debris. Most are not observed, but many fragments have been found. In 1997, Ms. Lottie Williams of Tulsa, OK, was hit by a piece of one while she was out walking. It didn't injure her, and the piece was light and cool. It turned out to be fabric insulation from a Delta II rocket's upper stage, which had been launched in 1996 and floated derelict ever since. More of the debris was found downrange, in Texas. Williams is the only person definitively known to have been struck by a piece of reentering orbital debris. You can read more about Lottie Williams here, holding up her small scrap of insulation.

It could have been worse; this tank is from the same rocket, found downrange in Texas.


February 1, 2003. STS-107 was Columbia's first flight in several years, having been sidelined while the other three Orbiters worked on ISS construction. She was scheduled to receive Discovery's Orbiter Docking System, so that she could take over missions while Discovery underwent a routine maintenance period. As she was aging, she was not expected to make many more flights; her last mission was tentatively placed for 2009, returning the Hubble Space Telescope from orbit. (More on that later.) The mission had been a complete success, and it was time to return home. Unbeknownst to NASA or the crew, a piece of foam insulation had punctured one of the reinforced carbon panels. During entry, hot plasma entered through this hole and melted through the aluminum ribs of the wing. The wing eventually tore away, and the entire vehicle rapidly broke up. Debris was scattered over hundreds of miles, and continues to be recovered to this day; last August, the continuing drought in Texas lowered the level of Lake Nacodoches sufficiently to reveal a tank from the fuel cell that provided Columbia with electrical power.

Recovered Columbia debris being identified, processed, and laid out for analysis by the accident investigation board.

Future Reentries

Low Earth orbit is full of objects, the vast majority inactive rocket parts, derelict spacecraft, and fragments. Reentries will keep on happening. The recently deactivated Rossi X-ray Timing Explorer has an estimated 1 in 1,000 chance of injuring a person. The Hubble Space Telescope has no means of returning to Earth under its own power; unless a robotic de-orbit system is developed in time, it will also return uncontrolled, with a 1 in 700 chance of injuring a person, largely due to its massive primary mirror.

Here's what's up there now, in low orbit and zoomed out to geosynchronous orbit. There's more going up all the time, so this will only get busier. Which one will come down next?

Cataloged objects in Low Earth Orbit and out to Geosynchronous Earth Orbit

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iStock // Ekaterina Minaeva
Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
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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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Why Your iPhone Doesn't Always Show You the 'Decline Call' Button
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When you get an incoming call to your iPhone, the options that light up your screen aren't always the same. Sometimes you have the option to decline a call, and sometimes you only see a slider that allows you to answer, without an option to send the caller straight to voicemail. Why the difference?

A while back, Business Insider tracked down the answer to this conundrum of modern communication, and the answer turns out to be fairly simple.

If you get a call while your phone is locked, you’ll see the "slide to answer" button. In order to decline the call, you have to double-tap the power button on the top of the phone.

If your phone is unlocked, however, the screen that appears during an incoming call is different. You’ll see the two buttons, "accept" or "decline."

Either way, you get the options to set a reminder to call that person back or to immediately send them a text message. ("Dad, stop calling me at work, it’s 9 a.m.!")

[h/t Business Insider]