Other investigations focused on flame behaviour in microgravity. As with many other physical processes on Earth, buoyancy affects the spreading patterns of flames as heated gas rises, drawing in gas from below to replace it. In space, however, such gravity-induced distortions are minimised and their shape and behaviour alter markedly. Studies of how fire behaves in space, and how to control it, have obvious applications in the design and testing of fire-fighting tools for use on board spacecraft and on Earth. On 26 June, DeLucas started the Smouldering Combustion in Microgravity experiment and began videotaping its progress for ground-based investigators.
Meade completed the experiment with its fourth scheduled run on 28 June, igniting polyurethane foam cylinders, sealed in clear Lexan, as sensors recorded temperatures and the spreading rate of the combustion process. "The experiment went very smoothly and we expect to get a lot of information as we analyse our data," said designer Carlos Fernandez-Pello of the University of California at Berkeley. "From what we've seen so far, the results seem to confirm a possible theory about the relative roles of cooling and airflow in smouldering combustion."
After performing another test, the Wire Insulation Flammability Experiment (WIFE) inside the Glovebox, which heated and burned electrical wires, Meade was described as "the coolest guy off Earth'' by experiment designer Paul Greenberg of NASA's Lewis (now Glenn) Research Center in Cleveland, Ohio. Other investigations studied the progress of flames along samples of Plexiglas and a special filter paper in an artificial 'atmosphere' containing nitrogen and argon. On 2 July, Dunbar successfully ignited the ashless filter paper in the Glovebox and downlinked video footage to experimenters.
Still more tests were conducted using a set of 10 candles, each measuring 2.5 cm long - similar to the kind that adorn birthday cakes - to examine the behaviour and shape of their flames in microgravity. Composed of about 80% paraffin and 20% stearic acid, the candles were lit by science crew members by pushing electrically controlled igniters through an opening in each candlebox. Immediately after ignition, the candles flared into spherical balls with bright yellow cores; within eight to 10 seconds, however, presumably due to soot, they turned blue and assumed hemispherical shapes about 1.5 cm in diameter.
This data was consistent with short-duration studies on board parabolic aircraft, which were able to simulate microgravity for up to 30 seconds, and even briefer drop-tower tests in the United States and Japan. It was speculated that the change in shape from spherical to hemispherical indicated that the flame was providing heat to the wick. Generally, the flames extinguished themselves within about a minute. ''We're overjoyed," said experiment designers Howard Ross and Donald Dietrich of Lewis Research Center. ''The observations [the crew] called down were invaluable, since they were able to report things we could not see on the video downlink.''
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