Earlier this week, Orbital ATK’s Cygnus cargo capsule, which has been attached to the International Space Station for the past few months, was filled up with more than 4,000 pounds of trash and released from the station out into space. A few hours later, a fire started inside the vehicle’s gut.
Multiple cameras and sensors gathered data about the blaze
Don’t fear, it was all apart of a NASA science experiment called Saffire-I — short for "safe fire" — which aims to study how fires behave in microgravity. For the test, a cotton-fiberglass material measuring 1.6 feet by 3.2 feet was lit on fire inside the Cygnus, while multiple cameras and sensors gathered data about the blaze. It was the largest controlled fire ever in space. NASA will be downloading all the data collected over the past week while the Cygnus is in space, but the space agency already posted a few videos from the experiment showing how the fire spread.
The first video shows how the smoke trails flow over the material, which is lit up green with LED lights.
After that, the fire starts, looking a bit like orange waves undulating across the green material. The entire burn lasted eight minutes, according to NASA.
Fires are a bit more unpredictable in space, due to the lack of gravity. Here on Earth, we can expect a flame to move up. A candle flame, for instance, heats up the surrounding air, causing those gases to rise and shape the flame upward. Cooler, heavier air moves down to take the place of the rising hot air, which helps to keep the flame going by replenishing the fuel. In space, air doesn’t weigh anything, so there’s no rising or falling of gases. Thus, candle flames form little spheres in space instead, as well as burn much more slowly and more cooly.
NASA has learned a lot about fire through experiments on the ISS, but all those combustions have been pretty small in order to limit mishaps. But since Cygnus is uncrewed, scientists could light a bigger fire without endangering astronauts. "Will an upward spreading flame continue to grow or will microgravity limit the size? Secondly, what fabrics and materials will catch fire and how will they burn?" says David Urban, the principal investigator of the experiment, in a statement. Hopefully, NASA will get the answers to those questions with this most recent experiment. If not, another Saffire experiment will launch on the next Cygnus capsule, and the space agency has ideas for even more flame tests.
As for this Cygnus, it will experience an even bigger fire soon. The spacecraft will deploy some satellites in the next few days and then on June 22nd, it will deorbit and burn up in Earth's atmosphere.