Feb. 13, 2007 Fires don’t break out very often on board orbiting spacecraft, but when they do, standard fire extinguishers aren’t necessarily the best way to put them out.
Oddly enough — after decades of spaceflight and a few fires along the way — nobody really knows yet what is the best way to put them out.
That’s what a team of five Viterbi School aerospace engineering students wants to find out. This March, the group, which founded a new student space exploration club called USC Students for the Exploration and Development of Space (SEDS), will have a rare opportunity to find out more about how fire behaves at very low gravity, or “microgravity” — when they conduct a flame experiment outside the bounds of gravity.
They will be flying aboard NASA’s modified KC-135 aircraft, sometimes referred to as the “Vomit Comet.” Stationed at Ellington Field, Texas, near the space agency’s Johnson Space Center, the KC-135 “weightless wonder” is the only experimental facility that can recreate specific gravities, such as lunar gravity, reduced gravity, Martian gravity, or a sustained hypergravity.
The USC team will be concentrating solely on microgravity, which is similar to conditions onboard the orbiting space station. Flying aboard the KC-135 will be Daniel Calvo, a junior aerospace engineering major and captain of the USC flame experiment; Emily Hedges, a junior aerospace engineering major; Adriel Carreno, a junior mechanical engineering major; and John Duncan, a junior aerospace engineering major. Alternates are Quinn Freyermuth, a junior mechanical engineering major, and Mikeala Blackler, a junior industrial systems engineering major.
“It will be exciting to be able to experience weightlessness, but right now, we are really rushing to get our experiment built and tested,” said Calvo. “If all goes well, we hope we’ll get some good data from this experiment and be able to say something more definitive about what kinds of fire extinguishers the astronauts should have for living and working in space.”
Calvo and his team competed against scores of undergraduate teams across the country in NASA’s Reduced Gravity Student Flight Opportunities Program. The program gives students nationwide a unique opportunity to purpose, design, fabricate, fly and evaluate a reduced gravity experiment of their choice aboard its one-and-only flying microgravity laboratory.
“Fire burns very differently in space than it does on Earth, especially in the microgravity environment that we have aboard the space shuttle or on the international space station,” Calvo said. “In this experiment, we will test three atmospheres — a carbon dioxide (CO2) atmosphere, a helium-based (He) atmosphere and a nitrogen-based (N2) atmosphere — to see how fast fire burns.”
CO2 is a radiatively active gas and is used as a fire suppressant in terrestrial fire extinguishers. According to the team, research indicates that CO2-based atmospheres will actually cause fire extinguishers to increase the burning rate of a flame. That's because extinguishers use a CO2-based fire suppressant, which increases the heat transfer by radiation to the flame. Helium is just the opposite; it is a radiatively inactive gas. A helium-based atmosphere is likely to have the opposite effect.
“If this turns out to be the case, then the fire extinguishers we use on Earth aren’t going to be as effective in space,” Carreno said. “We’re testing helium because it is a radiatively inert gas which may actually slow the burn rate of a flame in microgravity.”
The third experimental atmosphere — a nitrogen-based atmosphere — will act as a control, as well as to simulate the type of environment experienced in manned space vehicles.
Hedges said the team has been scrambling since fall semester to design and test the combustion experiment. They’ve relied heavily on guidance from faculty advisor Eugene Bickers, who is a physics professor and associate vice provost for undergraduate programs, and help from Paul Ronney, an aeronautics/astronautics professor in the Viterbi School and former NASA astronaut.
Physically, the experiment consists of a test chamber and stand, and wax balls that will be ignited and studied inside the chamber. The students will fill the chamber with each of the three gases — CO2, He and N2 — to create the three different atmospheres, then ignite and study the wax balls as they burn in each atmosphere.
The team will get two flight days aboard NASA’s “weightless wonder” KC-135 aircraft to conduct their experiment, which means they will have about 60 chances (2 flights x 30 parabolas/flight) in all to ignite and measure their fireballs in weightlessness. Four additional teams from other institutions, each with four team members, will be sharing the ride and running independent experiments simultaneously.
The KC-135 aircraft usually flies 25-to-30 parabolic maneuvers over the Gulf of Mexico during each flight, Ronney said. That roller coaster pattern provides about 25-to-30 seconds of hypergravity (about 1.8 G to 2 G) as the plane climbs to the top of the parabola and “noses over” to begin its descent. The low gravity is experienced as the plane is climbing toward the top of the parabola.
Calvo is particularly keen to see how the flames behave in a CO2-based atmosphere, because that would confirm his suspicion that the current CO2 fire extinguishers used by astronauts should be replaced.
“There hasn’t been a fire onboard a spacecraft in a long time, so people haven’t thought much about fire extinguishers or fire safety for a while,” Calvo said. “This is a good time to revisit the issue.”
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