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Friday, July 11, 1997 6 p.m. CDT
STS-94 Mission Science Report # 18s

The crew aboard the Space Shuttle Columbia has had another busy day conducting materials and combustion experiments in the Spacelab.

Today, crew members worked in the Glovebox to conduct additional Fiber Supported Droplet Combustion experiment. Mission Specialist Dr. Don Thomas spent most of the morning, and Payload Specialist Dr. Roger Crouch spent the afternoon, conducting the experiment to study the combustion process of large droplets of fuel.

"In this experiment we're burning heptane and hexadecane -- hydrocarbon fuels which are similar to gasoline," said co- investigator Dr. Benjamin Shaw of the University of California in Davis, Calif. "Hexadecane has a much higher boiling point than heptane and when you mix these two together some peculiar things happen."

"Specifically we're looking to see whether the fuel drop will have a bubble that will grow inside and then shatter the drop. Sometimes these flames will pulsate and we want to know when that pulsation occurs because that tells us what is going on within the droplet itself," said Shaw.

The Fiber Supported Droplet Combustion experiment allows scientists to study the burning of fuel droplets nearly one- quarter inch in diameter. The experiment will shed light on the role that convection plays in burning by introducing a controlled air-flow into the flame environment during the experiment.

Results of this experiment, led by Dr. Forman Williams of the University of California in San Diego, could lead to the efficient utilization of fossil fuels and reduction of air pollution.

This morning Linteris set up the Combustion Module -1 and conducted another run of the flame ball or Structure at Low Lewis-number experiment. This run of the experiment used a fuel mixture of hydrogen, oxygen and sulfur hexafluoride at one atmospheric pressure -- the same as on Earth. Linteris sparked the fuel mixture in the test chamber, producing one burning ball of flame. Upon a reburn attempt, another flame ball was ignited.

"We had a very successful burn and reburn this morning," said project scientist Dr. Karen Weiland. The initial flame ball burned steadily for the duration of the experiment -- 500 seconds.

The flame ball experiment is designed to determine under what conditions a stable flame ball can exist and if heat loss is responsible for the stabilization of the flame ball during burning. The experiment also examines how various mixture properties, such as fuel/oxidizer concentrations and temperature, affect the flame-ball's stability and existence.

Around noon, Thomas initiated a nickel sample from an experiment led by Dr. D.M. Herlach of the German Aerospace Research Establishment in Cologne in the TEMPUS levitation facility. This experiment studies the solidification velocity of dendrites -- tiny branching structures -- that form as metals solidify. The size, shape and structure of the dendrites have a major effect on the strength and usefulness of an alloy.

Measurements of the speed of dendritic solidification can be used to test and refine modeling of dendritic growth behavior. This type of experiment must be performed in microgravity because crystal growth can be greatly affected by connective fluid flow or buoyancy-driven motion, in molten metal. The low-acceleration environment in space effectively eliminates convection. Comparing space experiment data to those obtained on Earth will allow researchers to learn more about the effect convection has on dendrite growth. Information gained from this experiment could have applications in welding and casting.

Before taking a scheduled half-day break, Payload Commander Dr. Janice Voss performed a procedure to fix the top-view camera in the TEMPUS facility. The camera had stopped working earlier in the mission. The proceedure was a success, and the camera is operational. The side-view camera has remained operational throughout the mission and investigators have been able to receive data despite the malfunction of the top-view camera.

This afternoon, Crouch initiated the sixth and last sample run of the diffusion in molten semiconductors experiment in the Large Isothermal Furnace. This is the first time diffusion in semiconductors has been studied in space. Results of the experiment could improve semiconductors used in electronic components.

Ahead Payload Commander Dr. Janice Voss will perform a run of the flame ball experiment and Crouch will continue to perform the Fiber Supported Droplet Combustion experiment.

The next scheduled Public Affairs status report will be issued at approximately 6 a.m., July 12.


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