Spherical flame experiment onboard the ISS. Credit: NASA/Goddard Space Flight Center
The vacuum of space is one of the most, if not the most, inhospitable environments known to man, yet for astronauts, a far more immediate and unpredictable threat can ignite inside the very spacecraft systems designed to keep them alive: an uncontrollable fire.
While the recent flight of Artemis II showed that humanity can safely return to the lunar vicinity, a severe safety blind spot remains before we build permanent outposts. We do not actually know how fire behaves under the Moon’s faint gravitational pull. By intentionally burning fuel samples on the lunar surface, a bold new mission aims to expose the hidden, counterintuitive rules of extraterrestrial combustion. The goal is to prevent future lunar habitats from turning into fire hazards.
Anatomy of a Weightless Flame
On Earth, a flame acts like a miniature heat pump. Hot gas rises, forcing cold, dense air to rush in and take its place.
This continuous upward flow delivers a steady stream of fresh oxygen to the burning fuel. In the total weightlessness of space, that cycle breaks down entirely.
On Earth, the shape of fire is typically a teardrop or “tongue-like” shape. Without gravity pulling cold air downward, flames bloat into slow, spherical blobs. They feed exclusively on whatever airflow is already circulating in the spacecraft cabin.
NASA already knows a few things about how fire behaves in microgravity. It has spent decades studying these fire orbs in microgravity using drop towers—tall vertical shafts where payloads are dropped to simulate a few seconds of weightlessness—and inside detached cargo capsules near the International Space Station.
To decide what materials are safe to fly, engineers rely on a standardized test protocol known as NASA-STD-6001B. They hold a six-inch flame to a piece of fabric or plastic. If the material burns more than six inches upward or drips flaming debris, it fails.
But as NASA researchers point out in their mission outline, the safety test is “conducted in normal Earth gravity, with the assumption that if a material passes the 1G test, then it is considered safe for spaceflight.”
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Fire’s Goldilocks Zone
Flame ignited as part of the Flame Design investigation on the International Space Station. Credit: NASA
The Moon presents a distinctly different physical regime. It exerts about one-sixth of the gravitational pull we feel on Earth, but that’s still a lot more than the almost pure weightlessness experienced on the International Space Station.
This partial gravity creates a unique and unpredictable environment. It generates just enough upward airflow to feed a fire, but not enough to trigger a natural phenomenon called blowoff.
On Earth, blowoff happens when the rush of fresh oxygen moves too fast for the chemical reactions to sustain the flame. The rushing air effectively blows the fire out.
On the Moon, that airflow slows down. NASA researchers suggest that a “material that is marginally non-flammable on Earth” might actually become “flammable at a lower gravity level.”
In this slower environment, the chemical reactions have time to keep up with the incoming oxygen from the artificial habitat, according to the NASA researchers. Consequently, materials we consider perfectly safe on Earth might burn vigorously in a lunar habitat.
According to the project report, NASA researchers predict that “lunar gravity could be more hazardous since flame spread rate is a function of gravity peaks” in certain partial gravity environments.
Bringing Matches to the Moon
To confront this threat, engineers developed the Flammability of Materials on the Moon (FM2) mission.
Targeting a “planned launch date of late 2026,” NASA researchers will send a robotic, sealed chamber to the lunar surface. Inside, the automated FM2 system will systematically ignite four solid fuel samples.
Cameras, radiometers, and oxygen sensors will track how the fires behave over long durations. This allows scientists to move past the fleeting, unpredictable seconds of weightlessness achieved during parabolic airplane flights or drop tower experiments.
“The tests will provide benchmark data and are part of the larger effort to understand how lunar gravity will affect material flammability,” noted the NASA researchers in their report.
NASA is already preparing for Artemis III and Artemis IV, aiming to put humans back on the lunar surface. These future explorers will likely live in oxygen-enriched atmospheres.
While that air mix can simplify some life-support demands, it also makes fires easier to sustain. Understanding exactly how materials ignite in this specific atmospheric blend is paramount.
Right now, there is no practical way to perform full-scale material qualification tests on the Moon. Researchers acknowledge that broader testing will have to wait until humans have a longer-term presence there. But even a small set of early experiments could answer a critical question: do the materials we trust on Earth remain safe on the Moon?
That is why setting controlled fires on the lunar surface may be one of the smartest safety tests NASA can run. The goal is simple. Learn how flames really behave before astronauts move into habitats where a small fire could turn catastrophic.
