By BlueShift and AFP | 2026-01-16

When fire breaks out in the low-gravity, high-stakes conditions inside spacecraft or space stations, it behaves differently than it does on Earth.

So with anticipated missions to the Moon and Mars in the coming years, researchers from a number of nations are seeking to learn more about how flames spark and spread in space, and how best to stamp them out.

The deadly threat fire poses in space was first seen during the inaugural mission of NASA's Apollo program, which went on to put the first humans on the Moon.

Just days before the Apollo 1 mission was scheduled to launch in January 1967, its three crew members were killed by a fire that broke out in the spacecraft's cabin during a training exercise on the ground.

"At that time, the capsules were filled with 100% pure oxygen at low pressure, instead of atmospheric pressure, so the astronauts could breathe," explained Serge Bourbigot, a researcher at France's Centrale Lille institute.

"However the more oxygen you have, the more it burns," he said.

Since the Apollo 1 disaster, the oxygen levels in spacecraft carrying astronauts have been set to 21% -- the same amount as on Earth. But fire still acts differently in these cramped conditions, hurtling through the vastness of space.

The risk of fire

When you light a candle on Earth, the heat rises because hot air is less dense than cold air. But if you lit that candle inside a spacecraft or a station orbiting our planet, the heat would stay put because of the lack of gravity.

So instead of seeing a feather-shaped plume rise from the candle's wick, "you get a ball of flame," Bourbigot said.

"This ball will create and radiate heat, sending heat into the local environment -- the fire will spread that way," expanding in every direction, he added.

To find out more, Bourbigot and three other scientists have been awarded a grant from the European Research Council.

Their work has proved particularly timely because NASA recently recommended that oxygen levels be increased to 35% in new spacecraft and space stations, mainly to cut costs.

"With 35% oxygen, less pressure is needed inside the spacecraft, so the structure can be lighter," Bourbigot explained.

Heavier spacecraft require bigger rockets to launch them into space, making them more expensive.

But when oxygen levels rise, so does the risk of fire. So the grantees are investigating different ways to track and stamp out any space blazes in the future.

How flames behave

Guillaume Legros of France's Sorbonne University is trying to use acoustic waves to smother the flames.

Tests have already been carried out on parabolic flights, which simulate the weightless conditions of space for 22 seconds.

Bourbigot is meanwhile looking into flame retardants. While these chemicals work well on Earth, low gravity again throws up new hurdles.

Because smoke does not rise in the same way, it is more dense and "poses an opacity problem," Bourbigot said.

Florian Meyer from Germany's University of Bremen is developing sensors to closely monitor temperatures and track how fires would spread in space.

And fire safety researcher Bart Merci from Belgium's Ghent University is planning to digitally simulate how flames behave in low gravity.

To test their theories, a rocket is planned to launch within the next four years that will provide six minutes of microgravity to investigate how fire behaves in these conditions.

European aerospace manufacturer Airbus will build the rocket, which is set to launch from northern Sweden.

For their research, which is grouped under the Firespace program, the four scientists have received 14 million euros ($16 million) -- enough to fund their work for the next six years.

Fire safety research

NASA's Solid Fuel Ignition and Extinction (SoFIE) project is an ongoing series of experiments on spacecraft fire safety that are conducted within the Combustion Integrated Rack (CIR) on the International Space Station (ISS).

The CIR features a chamber where experiments can burn safely.

The microgravity environment on the ISS enables scientists to study the true nature of flames isolated and unaltered by gravity.

The resulting data can then be applied to mathematical models that predict how those materials would burn in lunar, Martian, or other environments.

The SoFIE project, which builds on NASA’s prior flammability research, directly supports the agency's Moon to Mars initiatives by focusing on astronaut safety, both aboard spacecraft and in future living spaces.

It has been studying the flammability of plexiglass, cotton-based fabrics, and other materials commonly used in spaceflight, under various conditions.

This will help NASA select materials and designs for spacesuits, cabins and habitats, and will help it identify the best ways to put out fires or smoldering materials in space on longer and farther missions.

"With NASA planning outposts on other planetary bodies like the Moon and Mars, we need to be able to live there with minimal risk," SoFIE project scientist Paul Ferkul of NASA’s Glenn Research Center in Cleveland said in February 2022.

"Understanding how flames spread and how materials burn in different environments is crucial for the safety of future astronauts."