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JUDY WOODRUFF: Now: how NASA is trying to fight fire with fire in space.
Researchers are conducting new experiments that would limit that particular danger for future space travel.
Science correspondent Miles O’Brien has the story. It’s part of our weekly series on the Leading Edge of science and technology.
JOHN GRUNSFELD, NASA: We are crossing an international boundary. We are on the U.S. side now, and now we are on the Russian Mir space station.
MILES O’BRIEN: By 1997, the Russian space station Mir was 11 years old and showing its age. During the fifth shuttle mission to the station, astronaut John Grunsfeld documented the warren of modules brimming with a disorienting maze of cables, hoses and trash.
JOHN GRUNSFELD: I feel like I am exploring a cave.
MILES O’BRIEN: Can you imagine being in a fire here?
U.S. astronaut Jerry Linenger lived that nightmare on February 23, 1997.
JERRY LINENGER, Former NASA Astronaut: The fire was basically in this region here with the flames shooting across this way.
MILES O’BRIEN: The source was a canister filled with chemicals designed to generate oxygen.
JERRY LINENGER: You have got a two- or three-foot flame, blowtorch-like in intensity, sparks flying off the end of it. It looks like a hundred sparklers all at once.
MILES O’BRIEN: Linenger and his Russian crewmates donned masks and frantically fought the fire.
JERRY LINENGER: The fire took about 14 minutes total, and 14 minutes is a long time with a roaring fire and a blackout from the smoke, and no place to go. And if it were any bigger, I’m pretty darn sure we would have lost that spacecraft.
MILES O’BRIEN: For NASA scientists and engineers, it was a big wakeup call.
GARY RUFF, NASA: One of the things that you learn is, we really didn’t have a way to put that fire out.
MILES O’BRIEN: Gary Ruff is a scientist at NASA’s Glenn Research Center in Cleveland, Ohio. This is where the agency does most of its research on fires in the weightless environment of space called microgravity.
GARY RUFF: They used water foam fire extinguishers that they had, but that probably at most just kind of cooled everything else around it and kept it from spreading.
MILES O’BRIEN: Ruff leads a team that is trying to learn more about big fires in space. So, the plan is to deliberately set one and watch what happens, really.
All right, so what are we looking at here, David?
DAVID URBAN, NASA: This is the Saffire-III module.
MILES O’BRIEN: David Urban is the principal investigator for the Spacecraft Fire Experiment, or Saffire.
We spoke beside Saffire-III, slated for launch at the end of 2016. The one currently in space, Saffire-I, is an identical box strapped inside a cargo ship. Once the craft makes its delivery, departs and is a safe distance from the International Space Station, it will be time to light the fire inside Saffire.
Fire on a spacecraft is a pretty scary thing, isn’t it?
DAVID URBAN: It’s a very small space. What you would normally tolerate in your house are completely non-tolerable in a spacecraft.
MILES O’BRIEN: NASA’s most painful fire lesson came in 1967, when three astronauts were killed during a countdown test on the launchpad in Florida. It prompted a lot of changes in spacecraft designs. The agency took great pains to eliminate flammable materials wherever possible.
But fires in microgravity are harder to predict.
A lot of unanswered questions about fires in microgravity, right?
DAVID URBAN: A huge number. Basically, we don’t really know how fast they will grow or how large they will get, nor do we really understand, given the way the spacecraft are built, how quickly that temperature and pressure rise will be a problem for the crew.
MILES O’BRIEN: On the ground, when you light a candle, the heat of the flame melts the wax. It pulls up into the wick. It vaporizes, and that is what fuels the flame.
So if gravity is pushing everything downward, what is it that makes a flame go upwards? Well, as it turns out, the flame is surrounded by higher-pressure air. And gravity is pulling down colder, denser air, meaning there is more pressure at the base of the flame. That’s what causes the flame to go up. It’s buoyancy. It’s the same thing that keeps a boat afloat.
In space, when the gravity meter reads zero, the cool, dense air no longer flows downward. Instead, the air puts equal pressure on the flame from all directions. The end result? Candle flames in space are spherical. Over the years, NASA has conducted several combustion experiments on small samples of paper, cloth, plastics and hydrocarbons in special chambers on Skylab, the space shuttle and station.
DAVID URBAN: But they have all been really small. And so one of the open questions that we have got is how large that flame can get.
MILES O’BRIEN: During the Saffire-I test, they will set fire to a piece of cloth just like this. It’s 75 percent cotton, the rest fiberglass to give it strength.
They will analyze the fire with sensors that measure temperature, airflow, velocity, carbon dioxide, and oxygen. But their main instrument will be two cameras and some controlled lighting.
The images in the data will be beamed back to Earth. When the experiment is done, the cargo ship will be will be guided to its own fiery end over the South Pacific.
The Saffire team is planning three more experiments, for a total of six. The fires will grow larger, eventually simulating a full-fledged spacecraft fire scenario.
GARY RUFF: Since we’re going to release the gases into the cabin, we want to have some material there that the crew would have to help clean up after a fire.
MILES O’BRIEN: Jerry Linenger would certainly not disagree with that.
JERRY LINENGER: Packing up. Time to head home.
MILES O’BRIEN: Linenger made it home safe and sound after all, but by the skin of his teeth.
JERRY LINENGER: People say how brave you were. I don’t know. Bravery, you have got to have an option. You have got to have an option to run.
MILES O’BRIEN: As NASA sets its sights on long-duration human missions to Mars, it really isn’t a question of if there will be a fire, just when and how will the crew be equipped to respond?
Miles O’Brien, the “PBS NewsHour,” Cleveland.
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