NASA Glenn researchers study results of Saffire-I experiment
Researchers at NASA’s Glenn Research Center are evaluating the results of the largest fire ever purposely set in space. The experiment called Saffire-I, which is a word-merger name for Spacecraft Fire Experiment, was conducted on June 14 inside a specially designed module aboard an Orbital ATK Cygnus cargo spacecraft.
The module, about the size of a cedar chest, contained a 1-foot by 3-foot (30-centimeter by 91-centimeter) cotton-fiberglass material card that was ignited by a hot wire. The event was observed by cameras and sensors and downloaded over the course of eight days to researchers at NASA Glenn in Cleveland, Ohio, and the Orbital ATK facility in Dulles, Virginia.
“No one had done an experiment on this vehicle in this way,” Saffire principal investigator David Urban told Spaceflight Insider, “so it was a new interface for everybody.”
Saffire-I was the first of three planned Saffire experiments scheduled to occur on three different Cygnus spacecraft flights. Each experiment is designed to allow researchers to study how flame behaves and spreads in zero-g.
Inside the Saffire-I module, the material was ignited inside an airflow chamber sealed and separate from its accompanying avionics and instrument bay.
“It ignited as planned, but it burned a little more slowly than we had anticipated,” Urban said. “So we did a few seconds of a bonus burn.”
Urban said the material was designed to burn forward, where the flame propagates downwind from the fan inside the experiment. He said if you blow on the flame, it will burn away from the source of air.
“That’s normally the fastest mode of flame-spread on Earth or in space,” Urban said, “That’s the most flammable condition. But in case it didn’t work we had a secondary igniter to ignite the far end. We turned off the flow a little bit before it hit the far end of the sample. Then we hit the second igniter and got about a centimeter of burn, and got the measurement on that flame-spread velocity as well.”
Determining flame-spread rate in zero-g is one of the main pieces of information researchers hope to gain from the Saffire data.
“It appears that flame-spread rate remains constant over a sample of this size,” Urban said. “It doesn’t seem to grow the way it would in 1-g. That was one of the big questions we needed to answer in getting a scale of what was our needed response time for a fire. On Earth, if a sofa is on fire, the fire grows at an exponential rate. As time goes by it gets worse and worse a lot faster. But in this sample in zero-g—the spread rate was constant. The fire didn’t ‘take off’ so to speak. That indicates that we may have a little more time to respond to a spacecraft fire.”
Urban and his team at NASA Glenn are continuing to study the data from Saffire-I even as Saffire-II is being prepared for launch aboard another Cygnus, the S.S. Alan Poindexter, in August.
Saffire-II will contain nine smaller samples, each being 2 inches by 12 inches (5 centimeters by 30 centimeters) long, with the samples being of different materials. Two of the samples are repeats of the cotton-fiberglass material on Saffire-I. Two are a thicker material similar to plexiglass. Four of them are different thicknesses of a silicon rubber material used on spacecraft called Nomex.
Urban explained that some of the Nomex samples that will be aboard Saffire-II are of thicknesses that cross the flammability threshold on Earth. As the thickness of the Nomex material is increased, it becomes non-flammable.
Urban said the material will likely behave differently in microgravity, and that they need to determine where that non-flammability threshold is in zero-g. The last sample is a very thick sample of Nomex that researchers are doubtful is possible to ignite regardless of gravity condition.
“But we are going to try,” Urban said. “We have to investigate if there are some unknown flammability properties of the material in zero-g.”
Saffire-III will launch aboard another Cygnus spacecraft sometime later this year. It will carry the same large sample as in Saffire-I, but researchers will increase the airflow rate for that experiment.
Saffire-I was launched aboard the Orbital ATK Cygnus cargo spacecraft named S.S. Rick Husband in March of this year. After docking with the International Space Station (ISS), its cargo of supplies and food were unloaded over the following weeks.
Once the spacecraft was emptied, trash from the ISS was then periodically stowed aboard the spacecraft for disposal. The spacecraft was unberthed on June 14 from the ISS and maneuvered far away from the station. Several hours later the Saffire-I experiment was conducted successfully aboard the spacecraft.
The S.S. Rick Husband remained in orbit another eight days while the data from the experiment was downlinked to Earth. The spacecraft was then deorbited on June 22 and burned up in the atmosphere over the Pacific Ocean.
NASA expects to learn much from Saffire-I and the next two Saffire experiments. It is hoped the knowledge gained will increase safety for astronauts aboard future missions to deep space and to Mars.
“It’s still a very new and exciting set of data for us,” Urban said. “We’ve got a lot to learn yet. Our scientists are just digging into it.”
Michael Cole is a life-long space flight enthusiast and author of some 36 educational books on space flight and astronomy for Enslow Publishers. He lives in Findlay, Ohio, not far from Neil Armstrong’s birthplace of Wapakoneta. His interest in space, and his background in journalism and public relations suit him for his focus on research and development activities at NASA Glenn Research Center, and its Plum Brook Station testing facility, both in northeastern Ohio. Cole reached out to SpaceFlight Insider and asked to join SFI as the first member of the organization’s “Team Glenn.”