When your home
is an aluminum spacecraft in Earth orbit
- hundreds of miles from the nearest fire station - stifling a potential fire
early and fast can be a lifesaver.
A team of scientists,
engineers and astronauts are
working to do just that by building better detectors to pick up even the
faintest wisps of smoke before a blaze erupts inside a spacecraft.
"You can't
operate a spacecraft with humans in it without having flammable materials
around," David Urban, a researcher at NASA's
Glenn Research Center who is working on the new detectors, told SPACE.com.
"It's an ongoing risk that we're always worried about."
That risk
crystallized last month during a brief scare aboard the International Space
Station, when its Expedition
13 crew reported a smoke-like
smell inside the laboratory's Russian segment.
The odor
prompted ISS flight controllers to declare a rare spacecraft emergency and was
ultimately traced to the leak of a
mild toxic liquid - not a serious fire like that which struck
Russia's Mir
Space Station in 1997. But the incident reinforced the value of robust
detection systems not just aboard the ISS, but on all future spacecraft.
"The
problem is, in all cases, they designed these [smoke] detectors just using
engineering judgment," Urban said. "[Our] goal is to provide real statistics to
guide the design of future detectors for the next vehicles."
Smoke
behaves differently in space than it does on Earth. In the absence of gravity, individual
smoke particles remain nearer to their source longer than their Earth
counterparts and ultimately clump together to form clusters that can be 10
times bigger than terrestrial smoke particles, researchers said.
"This is
important because if you're building a smoke detector, you should know what
size of smoke to look for," Urban said.
Bulky
smoke
During his
six-month tour aboard the ISS, Expedition 13 flight engineer Jeffrey
Williams worked with Urban and his team on the Dust and Aerosol measurement
Feasibility Test (DAFT) to test handheld smoke detection devices for future
orbital smoke experiments.
The
experiment revolved around a handheld device dubbed P-Trak - an off-the-shelf
air quality tool modified by NASA engineers for use in microgravity - which
uses an internal laser and optical sensor to detect aerosols and smoke
particles.
Williams
combined P-Trak with a modified home ionization smoke detector, a companion
dust sensor - aptly named Dust-Trak - and a four-gallon (15-liter) bag.
The astronaut then shot bursts of grade-A Arizona road dust, and used the
detection tools to measure the amount of material in the bag.
"We're
pretty happy with the runs we got in August," Urban said, adding that earlier
tests by ISS Expedition
10 commander Leroy
Chiao successfully sampled the station's interior atmosphere. "So now we have an idea of what the
space station dust environment is."
The space
station's atmosphere, it turns out, is relatively dust free. That's a good
thing since the presence of dust can set off the orbital laboratory's
light-scattering smoke detectors in false alarms. Finessing future spacecraft
detectors to be sensitive enough to catch fires and smoke early - but not to
the point that false alarms become common - will be a challenge.
"That's a
big concern," Urban said. "The more false alarms you get the less respect your
device gets both by the crew and the ground operations people."
There are
two primary smoke detectors inside the space station's U.S.-built
Destiny laboratory, though similar sensors also safeguard the Russian
segments, researchers said. Smoke detectors are also installed in each
laboratory rack that receives ventilation and power, they added.
The station
is also equipped with carbon dioxide-based fire extinguishers in the U.S. segments and a water-foam system in the Russian modules.
"Neither
has ever been used in the space station," Urban said.
Preparing
for ignition
The success
of DAFT - all six hours of its operations - clears the way for an upcoming
experiment in which ISS astronauts will purposely start fires in space.
Dubbed the
Smoke and Aerosol Measurement Experiment (SAME), the tests call for short controlled
fires to burn Teflon, Kapton tape, silicone, rubber and other spacecraft
materials and then measure their resulting smoke with a P-Trak detector.
"The
purpose of SAME is to gather the data that we need to determine particle size
distribution for these various smokes," said William Sheredy, NASA's SAME
project manager at Glenn, in a telephone interview.
SAME is
slated to launch toward the ISS aboard a NASA shuttle in June 2007. Astronauts
will install the smoke-detecting sensors and other equipment inside the
station's microgravity science glove box, and then ignite the tiny orbital
fires. A shuttle smoke detector will also be included to measure its
performance, researchers said.
Unlike the
handheld DAFT experiment, which relied on astronaut input via a keypad, SAME is
designed to function autonomously during testing runs.
"As we go
to more autonomous systems we need to have a more autonomous fire detection
system," Urban said.
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