[SciShow Intro Plays]

Caitlin: Usually, fire inside a spaceship is very bad news. There’s lots of oxygen, lots of electricity, and pretty much no way for smoke or heat – or people – to escape. But soon, NASA is going to light a fire inside a spacecraft. On purpose!

Fires out in space have been pretty rare. But when the Russian space station Mir caught fire in 1997, the fire extinguishers on board weren’t big enough to put it out. All the crew members could do was spray around the fire and hope that it didn’t spread too far before it ran out of fuel, which it thankfully didn’t. So with long-term missions to places like Mars being planned, NASA wants to learn more about how fires spread inside of spaceships – and how to put them out. There have been a couple of small tests on the shuttles and on the International Space Station, but, understandably, no one on board wanted to just start setting big fires and seeing what happened.

Enter the Spacecraft Fire Experiment -- aka Saffire -- which is exactly what it sounds like: NASA is going to set stuff on fire in a spacecraft. Just one without people on it. To understand why fires in space should be any different, we need to start with what we know about fires down here on Earth. Fire is really just an energetic chemical reaction where oxygen rapidly bonds with something hot. Bonding with oxygen often releases energy, which makes more atoms start bonding with oxygen, and then the process keeps going for as long as there’s oxygen and fuel available.

Physics and chemistry are the same everywhere in the universe, so this part won’t be any different in space. But fire’s shape and the way it spreads will be different. When something like a candle burns on Earth, the fire has a pretty characteristic shape: there’s the thick bit at the bottom and the thinner flickering bit at the top. This happens because the flame heats the air around it, making it less dense. This hot air rises while cooler, denser air falls in toward the flame from the sides, bringing more oxygen with it. But hot air only rises because of gravity, and gravity doesn’t act the same way when you’re in orbit. That’s why, if you light a candle in space, you don’t get a nice teardrop shape. Instead, you get a sphere of fire.

Oxygen still finds its way in, but heat doesn’t escape as quickly. This means that fires out in space might be harder to put out, and they might be able to last longer and on less oxygen than fires here on Earth. But there’s still a ton that we don’t know yet -- which is where Saffire comes in. The experiment will take advantage of the fact that every so often, NASA or some other space agency sends a capsule up to the ISS with supplies in it. The astronauts unload all of the supplies, load the capsule back up with all of their garbage, and then send it back toward the Earth, where it and all of its contents burn up when they hit the atmosphere.

This week, NASA launched one of these capsules -- but this one had a special box onboard, with cameras, thermometers, a couple of other instruments, a 1-meter-by-0.4-meter piece of cloth, and a way to light that cloth on fire. In a few months, that capsule is going to detach from the ISS. About a day later -- before it re-enters the atmosphere -- the lighter inside the capsule will set the cloth on fire. And then, scientists are pretty much just gonna wait and see what happens.

The cloth is much bigger than any flame experiments that have been done in space before, so it should give scientists a much better idea of how flames spread in space and what they do in response to things like air flowing past them. But NASA isn’t stopping at one test. There are going to be at least five more flame tests within the next few years.

Some will test all kinds of different materials, to see how fire spreads on and between them all. Others will focus on fire prevention and ways of stopping a fire once it’s started. The hope is that whether astronauts are hanging out in low-Earth orbit or headed to Mars, if a fire breaks out, they’ll know what to do. I mean, it would be nice if nothing ever went wrong and everything that shouldn’t be on fire stayed not on fire. But just in case, you know?

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