What happens when a space station catches fire? No-one's quite sure, so Nasa is planning to conduct a slightly-scary experiment to find out.

The Cygnus capsules that carry supplies to the International Space Station normally fall back to Earth after their mission and burn up in the atmosphere. But the next one, which launches on 23 March from Cape Canaveral in Florida, will be incinerated higher up instead.

Once the supplies have been delivered and the capsule has undocked and made it to a safe distance from the ISS, ground control engineers will trigger a fire on board. It'll be monitored with cameras as well as temperature, oxygen and carbon dioxide sensors to find out what happens, and is expected to only last 20 minutes or so.

Nasa is interested in the size of the flames, along with the speed of their spread, the heat output and how much gas is emitted. The agency wants to know how microgravity and a limited oxygen supply affect these factors, allowing it to build better fire detection and suppression systems for its spacecraft.

Extinction Risk

That'll be important with a seven-month trip to Mars on the horizon. A manned mission is expected in the next couple of decades, paving the way for possible future colonisation of the red planet. SpaceX founder Elon Musk has spoken of the need for humanity to colonise other worlds to prevent planetary disasters from resulting in extinction.

The work "is crucial for the safety of current and future space missions," says Gary Ruff, an engineer heading up the experiment. "Understanding fire in space has been the focus of many experiments over the years. While many small, centimeter-sized fires have been lit in space before, to really understand fire, you've got to look at a more realistic size."

After the experiment is complete, what's left of the capsule will remain in orbit for a few more days before slowly falling back to Earth and burning up in the atmosphere.