I
on an upcoming shuttle flight an
experiment will be conducted to study
fire in the microgravity environment of
Earth orbit the solid surface combustion
experiment or ssce was built at the NASA
Lewis Research Center in Cleveland Ohio
to study the details of a fire spreading
over a small solid fuel sample on earth
gravity causes the hot gases in a flame
to rise this air motion called buoyant
convection brings fresh oxygen to the
flame and effects the heat carried
forward to ignite the fuel ahead of the
flame buoyant convection is one of the
more difficult aspects of fire for
scientists to understand in microgravity
boy and convection oven disappears
without convection the flames oxygen
supply and forward heat transfer depend
upon different physical mechanisms these
other mechanisms are present in normal
gravity but are overwhelmed by boy and
convection by performing the ssce
experiment in microgravity scientists
will be able to observe these simpler
flame spread mechanisms directly
with the inside gain from this
experiment scientists will better
understand how the complex system of
physical and chemical mechanisms
interact in fires on earth several years
ago NASA began investigating the
possibility of doing experiments in the
shuttle on combustion topics one being
droplet combustion another flame
spreading over solids and a third being
pre-mixed combustion at that time I was
doing flames spreading experiments and
had proposed to NASA an experiment to be
conducted on the shuttle and described
the key features of the experiment and
that experiment was ultimately designed
by people at NASA Lewis technicians at
Lewis built the hardware and performed a
series of exhaustive tests to show it
would work once it was launched in the
shuttle
scientists and engineers utilize special
ground-based facilities for testing
experiments in microgravity dropped
hours at the NASA Lewis Research Center
in Cleveland Ohio and special aircraft
at Lewis and the Johnson Space Center in
Houston Texas provide a few seconds of
microgravity at a time to obtain a hint
of how the experiment will work in orbit
at the heart of the ssce a sealed vessel
filled with an atmosphere of oxygen and
nitrogen houses a single sample of solid
fuel the test samples are materials like
paper that burn easily and air the
flight specimens are mounted in a
special holder that keeps them secure
during the rigors of a shuttle launch
the sample holder is bolted into the
test chamber and the chamber is sealed
and filled with a test atmosphere before
the hardware is placed in the shuttle in
flight the experiment is started by a
simple computer igniting the sample to
movie cameras are activated by the
computer to photograph the flame through
the windows in the chamber the ssce is
scheduled to fly aboard the shuttle
eight times since October 1995 flights
have been completed
in the first three tests and ashless
filter paper was burned in fifty percent
oxygen at three different pressures this
is an edge view of the burning paper at
higher test pressures the flame produces
more soot and is therefore brighter the
flame is photographed from both the top
and the side to gather detailed
information about the flame shape at two
times normal atmospheric pressure the
flame is very City the soot particles
glow providing the familiar bright
orange flame before each flight shuttle
astronauts are trained in both the
scientific objectives of the experiment
and how it is to be operated
his life in July 1992 aboard the shuttle
in the United States microgravity
laboratory usml won the ssce experiment
burned another ashless filter paper
sample in an atmosphere of thirty-five
percent oxygen and normal atmospheric
pressure during the STS 47 mission
mission specialists J AB perform the
ssce experiment under thirty five
percent oxygen and one and a half times
normal atmospheric pressure the final
three flights of the solid surface
combustion experiment will be used to
test the flames spreading
characteristics of a thick fuel this
fuel p.m. ma is more commonly known as
plexiglass variations of atmospheric
pressure and oxygen content will be
similar to those for paper tests the
experiments being conducted to gather
information that will ultimately allow
us to improve the fire safety aspects of
space travel from the point of view of
material selection and also extinguisher
development and in addition flames
spreading is a fundamental scientific
problem has been investigated for a
number of years and by doing experiments
in reduced gravity we hope to be able to
answer some of the questions that remain
about that scientific phenomenon