How does a fire grow in space?
That's the question that NASA aims to answer through its Saffire experiment, a three-part investigation of how fire spreads in a microgravity environment that launched in March.
The experiment began its second leg on Monday, when mission controllers on the ground ignited NASA's Spacecraft Fire Experiment-II, otherwise known as Saffire-II. Saffire-II will take place aboard the private, uncrewed Cygnus cargo spacecraft, which departed from the International Space Station on Monday after a monthlong stay.
The goal of the Saffire experiments, researchers say, is to provide a better understanding of how different materials propagate flames in space, information that NASA says is "immensely important" when it comes to developing new spacecraft, subsystems, and instruments.
"A spacecraft fire is one of the greatest crew safety concerns for NASA and the international space exploration community," said Gary Ruff, Saffire project manager, in a March news release.
Saffire-I, the first experiment in the series of three, burned a piece of cotton-fiberglass cloth that was 1.3 feet wide by 3.3 feet long aboard a different Cygnus spacecraft in June. The fire that ensued was the largest intentionally set in space, according to NASA officials.
Next, Saffire-II will burn a mix of nine different materials routinely used in space to see how each reacts to flames, including flame retardant fabrics used for astronaut clothing, structures used for storage containers and silicone composites, and the acrylic glass used for spacecraft windows.
Each remotely-operated experiment will take place inside a 3x5 foot module, as Lonnie Shekhtman reported for The Christian Science Monitor in March:
The 3- by 5-foot experiment box will be split into two compartments. On one side will be a computer and instruments such as sensors, high definition video cameras and signal processing equipment. They will measure oxygen, carbon dioxide, heat, pressure and flame growth, and record the flame.
The other side of the box will hold the equipment that will ignite the flame and burn the materials inside, all of which are used routinely for astronaut clothing and for other things on spacecraft.
The goal of the experiment, according to principal investigator David Urban, is to answer two questions: "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?"
The Cygnus spacecraft used for Saffire-II, which is designed to be disposable, will stay in orbit until Nov. 27, after which it will be "steered into a fiery death in Earth's atmosphere," Space.com reports.