A Hot Topic in Space Travel
by David Pescovitz
Using
an apparatus designed in his lab, Fernandez-Pello and his
team have been able to rank and classify the ignition time
and temperature of a wide range of materials used on board
spacecraft. His research provides the conceptual framework for experiments NASA will begin in two years on the International Space Station.
(Click for larger image.)
Peg Skorpinski photo
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NASA is looking
to Berkeley researchers to help solve a burning problem in spacecraft
design. With increasingly longer missions on the horizon, mechanical
engineering professor Carlos Fernandez-Pello and his team are testing
the flammability of the materials used aboard spacecraft to help
minimize the likelihood of a blaze in space.
"Spacecraft designers must have accurate information so they know
which materials to use where," says Fernandez-Pello, director of
the NASA-funded Microgravity Combustion Laboratory. "We can't build
spacecraft out of steel, right? So we really do have to know which
materials are flammable and which are not."
Historically, NASA designed spacecraft under the assumption that
materials that don't burn easily on Earth aren't flammable in space
either. Fernandez-Pello's research results turned the tables on
that assumption.
"After conducting the first tests in zero gravity, we were all surprised
to find out that materials ignite more easily and burn faster in
spacecraft than in earth's gravity," Fernandez-Pello says.
Fire
is an extremely dangerous and very real possibility aboard
the International Space Station. Several incidents of overheated
and charred cables and electrical components have already
occurred on the Space Shuttle — the craft used to transport
equipment and personnel to the space station.
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The reason for
the quick ignition, he explains, is that the lack of gravity prevents
the fire from inducing buoyant air currents. On Earth, bouyancy-induced
air cools a burning material by drawing in colder air which suppresses
the fire. Conversly, cooler air brings fresh oxygen which fans the
fire. The trick, Fernandez-Pello says, "was to determine if conditions in space, where only low velocity ventilation currents are present, would favor the cooling factor or the fresh oxygen factor, because that's what determines flammability."
To study the materials' flammability, the Berkeley researchers used
a testing device developed in Fernandez-Pello's lab. The Forced
Ignition and Spread Test (FIST) consists of a small wind tunnel
equipped with an external radiant heat flux. The materials are exposed
to both the radiant heat and the air currents present in spacecraft
to determine the time it takes for each sample to ignite. But how
does one replicate zero gravity?
Riding
the notorious "Vomit Comet," where Fernandez-Pello
and his research team have a 30-second window to run their
flammability experiments, requires efficiency, pluck, and
a strong stomach.
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Hitch a ride on the Vomit Comet. Technically known as the NASA KC-135
airplane, the Vomit Comet is named for its parabolic flight pattern,
not unlike the path of a roller coaster but at an altitude of 30,000
feet. At the peak of each parabola, zero gravity kicks in for 20
to 30 seconds, just enough time for Fernandez-Pello to fire up the
FIST and grab his measurements.
Currently, the Berkeley researchers are measuring the flammability
of acrylic plastics, blended poly-propylene with fiberglass composites,
and the laminated epoxy glass common to circuit boards. According
to Fernandez-Pello, many of the materials used in today's spacecraft
ignite as much as 50 percent faster in zero gravity conditions than
on earth.
"It turns out that the cooling effect of air currents is much more
important on Earth than we realized," he says. Future tests are
slated to be conducted by astronauts aboard the International Space
Station, with the first flight manifested for October 2004.
As for the Vomit Comet, "you get used to it," Fernandez-Pello says.
"It's actually a fantastic experience."
This article is based on a feature in the new issue of Forefront,
the College of Engineering's thrice-yearly print magazine.
Carlos Fernandez-Pello's home page
Microgravity Combustion Laboratory
NASA KC-135 "Vomit Comet"
Lab Notes is published online by the Public Affairs Office of the UC Berkeley College of Engineering. The Lab Notes mission is to illuminate groundbreaking
research underway today at the College of Engineering that will dramatically change our lives tomorrow.
Editor, Director of Public Affairs: Teresa Moore
Writer, Researcher: David Pescovitz
Designer: Robyn Altman
Subscribe or send comments to the Engineering Public Affairs Office: lab-notes@coe.berkeley.edu.
© 2002 UC Regents.
Updated 11/1/02.
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