Back in October, the Cygnus CRS OA-5 mission (aka. the Orbital Sciences CRS Flight 5) rendezvoused with the International Space Station. As part of Orbital ATK craft’s sixth Commercial Resupply mission to the ISS, the unmanned spacecraft spent the past month berthed with the station, delivering 2,268 kg (5,000 pounds) of cargo and experiments and taking on 1,120 kilograms (2,469 pounds) of trash.

As of this Monday, November 21st, the spacecraft – named the “S.S. Alan Poindexter” in honor of the deceased Space Shuttle commander who died in 2012 – separated from the station’s Unity Module, and will spend the next week performing standalone operations. These have included the much-anticipated Spacecraft Fire Experiment 2 (aka. Saffire-II), which is managed by NASA’s Glenn Research Center.

This experiment, which began just five hours after the shuttle detached from the station (and after it conducted an orbit-raising maneuver), involved the Cygnus controllers deliberately starting a fire inside the spacecraft’s pressurized cabin. The purpose of this was to investigate how fuel combustion works and fires grow in a microgravity environment.

How fire behaves in space is one of the least understood hazards facing crewed exploration. Until now, research has been limited, and for obvious reasons. Starting a controlled fire in a microgravity environment, especially when you don’t even know how it will behave, is an extremely risky venture. All previous tests that were carried out were severely restricted in size, and yielded very little information.

In contrast, the uncrewed portion of the Cygnus mission offers NASA scientists a rare opportunity to conduct a microgravity fire test aboard a spacecraft. Not only are they hoping to address how fires can ignite, but also how large they can grow in microgravity, how they may consume materials the spacecraft is built from, and eventually die.

As Jitendra Joshi, the technology integration lead for NASA’s Advanced Exploration Systems division, said in an interview with Spaceflight Now, such tests are critical for developing fire countermeasures:

“One of the least understood risks in space is how fire propagates (and) starts. How do you control the fire? How do you detect the fire? All these things. You can’t call 911 like on Earth to come help you.”

In addition to being pressurized, the inside of the Cygnus spacecraft also contained samples of material that are commonly found aboard the ISS. NASA was also sure to include materials that would be included in future tests of the Orion capsule, since such tests are of extreme importance to their “Journey to Mars” and other long-range, long-duration missions.

This was the second experiment conducted as part of the Saffire program, which is managed by NASA’s Advanced Exploration Systems Division, part of the Glenn Research Center. It follows on the heels of the highly successful Saffire-I experiment, which took place in July of 2016. In that experiment, samples of a cotton-fiberglass blend were ignited inside an enclosure aboard a Cygnus vehicle, which consisted of a flow duct and avionics bay.

The samples themselves measured 0.4 meter wide by 1 m long, and were ignited by a hot wire inside an enclosure measuring half a meter wide, 1 meter deep and 1.3 meter long. Prior to this experiment, the largest fire experiment that had ever been conducted in space was about the size of an index card.

The Saffire-II experiment (the second of three proposed fire tests) began just after 18:15 Eastern Time (23:15 UTC ) on November 21st, as the first of nine samples was ignited aboard the craft. This time around, the samples included a cotton-fiberglass blend, Nomex (a flame resistant material used commonly aboard spacecraft), and the same acrylic glass that is used for spacecraft windows.

The nine samples burned for a total of two hours before dying out, and yielded much useful information. As Gary Ruff, Saffire’s project manager, said in a previous NASA press release:

“A spacecraft fire is one of the greatest crew safety concerns for NASA and the international space exploration community. Saffire is all about gaining a better understanding of how fire behaves in space so NASA can develop better materials, technologies and procedures to reduce crew risk and increase space flight safety.”

The third and final experiment for the Spacecraft Fire Experiment series (Saffire-III) is scheduled to take place during the OA-7 mission, which is scheduled to take place in March of 2017. With all three experiments complete, NASA hopes to have accumulated enough data to help guide the selection and construction of future spacecraft, subsystems and instruments.

They also hope that these experiments will help mission planners come up with operational protocols designed to address fires during future crewed missions. These will be especially handy during missions where astronauts don’t have the option of exiting to a docked spacecraft and returning to Earth (as they do aboard the ISS).

The Cygnus craft is now moving on to deploy the four LEMUR CubeSats, which will happen on Friday, November 25th. These CubeSats are part of a growing community of satellites that provide global ship tracking and weather monitoring services.

Following this, Cygnus will remain in orbit for two more days before conducting two burns that will cause it to deorbit and burn up in out atmosphere – which will take place on Sunday, November 27th.

Further Reading: NASA Spaceflight, Spaceflight Now, NASA AES – Saffire