NASA intentionally lit a fire in one of its spacecraft, turning the Cygnus that had just delivered supplies to the International Space Station into a laboratory to see how future disasters might impact crewed missions to the Moon and, later on, Mars. While space itself lacks the oxygen for fire to be an issue, crewed spacecraft like those NASA intends to use for its Artemis missions need to provide a breathable atmosphere for the astronauts onboard.
That raises a big safety problem, since not only does that present a fire risk, but the ways in which fire actually behaves in low- or zero-gravity aren’t still fully understood. As a result, NASA has been running the Spacecraft Fire Safety Experiments, known as Saffire, to explore how large-scale flame growth occurs in space, and how different materials affect its spread.
“Understanding how fire behaves in microgravity, and how different materials propagate flames in space is immensely important for the development of future crew spacecraft,” NASA explains. “It also will help inform operational protocols for dealing with fire emergencies, particularly when astronauts do not have the ability to exit a spacecraft or quickly return to Earth.”
The first Saffire-I mission dates back to July 2016, with Saffire-V running on January 13. NASA used Northrop Grumman’s CRS-14 cargo ship, which had just finished a resupply mission to the ISS. It was selected because – unlike, say, SpaceX’s Dragon spacecraft – it’s designed to be single-use. Normally, after taking a hold-full of cargo to the orbiting research platform, Cygnus is filled with trash and then allowed to burn up on re-entry through Earth’s atmosphere.
That makes for an ideal test bed for larger fire experiments than NASA had previously been able to safely undertake. The Cygnus is fitted with remote sensors to track how temperature and carbon dioxide levels change, together with a so-called Far-Field Diagnostic (FFD) that tracks overall spacecraft atmosphere, along with flame growth.
Saffire-V was the first of the fire test missions to replicate the sort of atmospheric conditions within the capsule that human spacecraft might adopt. After departing the ISS on January 6, it was remotely filled with oxygen to 34-percent and with pressure at 8.2 psia, and then the fires lit on multiple samples. Perhaps unsurprisingly, the presence of oxygen only exacerbated the danger.
“The elevated oxygen levels show more energetic flames, which would have a larger impact on the vehicle,” Gary A. Ruff, Saffire project manager at NASA’s Glenn Research Center in Cleveland, explains. “The Saffire-V data will allow us to model fire scenarios and increase our confidence in safety strategies.”
An upcoming Saffire-VI mission is already being prepared, as NASA looks not only at how fire spreads and different materials hold up to that, but how fire detection, combustion product monitoring, and post-fire cleanup can be handled in space.