[Intro plays]

Reid: When it comes to space travel, there are all kinds of dangers to watch out for -- which is why astronauts spend years training to deal with things like equipment failure. But sometimes it’s the little, unexpected dangers that can cause big problems. Like tin whiskers, for instance.

They may sound like something you’d find on a cute robot kitten, but these things are dangerous. See, metals with low melting points, like tin, zinc and cadmium, can spontaneously sprout microscopic whiskers little threads of metal that can extend for several millimeters like creeping vines. Scientists still aren’t really sure why they happen, but the whiskers seem to grow in places where there’s some mechanical stress on the metal say, if it’s compressed a tiny bit.

Either way, whiskers are a problem, because those metals are often used to plate electronics, and the whiskers are conductive. So you can end up with a kind of electrical bridge between separate parts, which short-circuits them. That can be a really big deal even on Earth, where whiskers have led to pacemaker recalls and caused temporary shutdowns in nuclear power plants. But in the near-vacuum of space, they can be even worse.

At high voltages and low pressures, the whiskers can vaporize into plasma, causing what’s known as a metal vapor arc. These vapor arcs carry a lot of current, and can completely destroy electronics. In fact, metal vapor arcs were responsible for the failure of at least four commercial satellites, and they broke one of the instruments on the Cassini orbiter. And it’s hard to make sure that whiskers don’t happen. But NASA has stopped using plating made of pure tin, zinc, or cadmium, which helps. Another option is to coat the metal in a protective layer that stops the whiskers from getting very far. Otherwise, you could end up with electronics that randomly short-circuit and fail, which is not ideal on a spaceship or satellite.

But even with all their equipment working properly, humans in space can still be in danger. Because even though it’s probably not something you normally think of as risky, in space, sleeping is tricky for a whole bunch of reasons. For one thing, astronauts have to anchor their sleeping bags to a wall to avoid sleep-floating through the cabin. And while the possibility of waking up with your head banging against the ceiling is probably pretty annoying, the real danger of sleeping in space is the risk of getting killed by your own breath. Not morning breath -- I’m talking about carbon dioxide poisoning.

Humans exhale carbon dioxide. It’s a natural byproduct of our cellular metabolism, but it’s also very toxic to us. Down on earth, the air is about 0.04% CO2, and not usually a human health concern. But CO2 concentrations can get a lot higher in a spacecraft’s tight cabin quarters, and you can’t exactly open a window to grab a breath of fresh air. Warm exhaled air doesn’t rise in space, so if you’re sleeping tethered to a wall, that air will just linger around your mouth, eventually creating a big bubble of CO2. And that’s really bad news.

A CO2 concentration of 1% may leave you feeling drowsy, but a 5% concentration will leave you headache-y, dizzy, and confused. And at 8% or more? You’re dead. Of course, spaceships -- and the International Space Station -- have systems that filter out CO2 and circulate oxygen, but astronauts still need to make sure there’s enough airflow near their sleeping pods so that death bubble never forms.

Other kinds of human waste can be space hazards, too. And that’s something we learned about the hard way. The old Russian Mir station had a toilet system on board that vaporized urine and shot it out into space. That method seemed to work well enough -- at least, until scientists realized that the cosmonauts’ pee froze into tiny crystals that stayed in orbit for several weeks. And because even a dust-sized particle can be dangerous when it hits with the speed of a bullet, their pee came back to haunt them.

Before the Mir was purposely burned up in the atmosphere in 2001, its solar panels had lost about 40% of their effectiveness. Being continually battered by frozen pee for 15 years will do that. Today the ISS recycles its urine, which gets rid of the danger of pee debris, and has the added benefit of providing the crew with extra drinking water. So cheers to learning from past mistakes.

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