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Thursday, July 10, 1997, 7 a.m. CDT
STS-94 Mission Science Report # 15s

The crew of the Microgravity Science Laboratory mission and science teams on the ground worked steadily through the night, continuing to conduct fundamental scientific research in the areas of combustion science, fluid physics, materials science and biotechnology.

Payload Commander Janice Voss worked in the Combustion Module last night to conduct an experiment to study the burning processes of very weak mixtures of fuel and air in low- gravity. During the experiment, a mixture of hydrogen, oxygen and sulfur hexafluoride -- a combination that does not readily ignite -- was used in the facility. “We were able to get it to burn. The burn and reburn were both extremely successful,” said investigator Paul Ronney of the University of Southern California in Los Angeles. This is significant because these are the weakest flames ever burned. They will not burn on Earth.

Findings from this study may be used to build better models of weak combustion processes which may be applied to the design of cleaner, more efficient-burning fuel engines. “We know that if we can burn weaker mixtures in our engines, we could indeed get higher fuel efficiencies, with lower pollutant formation,” said Ronney.

Overnight, Payload Specialist Dr. Roger Crouch and Mission Specialist Dr. Donald Thomas conducted two tests of the Bubble and Drop Nonlinear Dynamics experiment in the Middeck Glovebox. During the experiment, acoustic pressure, or sound, is used to position the bubble in the center of a water-filled container and then flatten it. Researchers are measuring the bubble’s movement as the shape of the bubble changes. “This reveals the mechanical properties of the bubble under large forces, or distortions,” said investigator Dr. Anthony Hmelo of Vanderbilt University in Nashville, Tenn. “These properties are very difficult to model, so we are conducting this study to better understand fluid physics in general and improve theoretical models.”

Findings from this investigation may also have applications for improving industrial processes. “There are a range of industrial processes that depend on drops for operation,” said Hmelo. “For instance, the combustion of fuels, the same processes being studied in other experiments aboard Spacelab, depends on the kinds of fluid physics we are investigating in the Middeck Glovebox.”

Crouch performed a scheduled disk change-out in the Quasi-Steady and Space Acceleration Measurement system. The system is one of four on board the Shuttle which detects and records the small, unavoidable disturbances in the near-zero gravity of the environment of the Spacelab. Science teams rely on the information, downlinked in near-real-time, to determine the effect of the disturbances on experiments.

In the Large Isothermal Furnace last night, Crouch began the fourth of six planned runs of an experiment to study the diffusion process of tracers, or impurities, in molten semiconductors. Diffusion is the process by which liquid metals mix without stirring. The experiment is a fundamental scientific study to measure the thermophysical properties of germanium, an element widely used as a semiconductor. Findings from the study may have applications for improving the performance of electronic components made from semiconductor materials, such as transistors and integrated circuits.

Early this morning, Payload Specialist Dr. Gregory Linteris reported “fantastic” burns in the Droplet Combustion Experiment. During the experiment, heptane fuel droplets are burned at different pressures and oxygen concentrations. Runs conducted this morning were at one-half atmospheric pressure, half of what it is on Earth, in oxygen concentrations varying from 25 to 40 percent.

Results of each test may be different depending on the pressure, oxygen and size of the droplet. “Three things can happen,” said project scientist Dr. Vedha Nayagam of NASA’s Lewis Research Center in Cleveland, Ohio. “The droplet can not ignite; it can ignite and burn out partially, leaving a droplet of fuel; or it can ignite and consume the droplet, burning out completely.” The Droplet Combustion Experiment is studying these scenarios.

The experiment is also interested in determining the complex chemical processes which occur when the flames are extinguished. “By understanding the chemistry which occurs, we can burn them more cleanly, more efficiently, because we know how they work,” said Nayagam.

Later, Linteris began an experiment in the TEMPUS levitating furnace facility to collect fundamental measurements of an undercooled sample of palladium-silicon. Undercooling is when a liquid remains fluid when cooled below its freezing point. During the experiment an electromagnetic pulse is used to squeeze, then release the sample being levitated in the facility. Researchers then gather data on the resulting oscillations, or changes in the sample’s shape. “By measuring the oscillations, we can determine the surface tension and viscosity, or resistance to flow,” said researcher Bob Hyers of the Massachusetts Institute of Technology in Cambridge, Mass.

“We are using a new technique which is allowing us to measure the viscosity of these samples for the first time, measurements which can’t be obtained on Earth. And even some of the surface tension measurements are a first,” said Hyers. This information may be used to improve materials processing techniques on Earth and in turn products manufactured from these processes. “The study is providing us with fundamental measurements for modeling industrial materials systems. Without the right parameters, you can’t model systems,” said Hyers.

Ahead, Linteris will continue to conduct the Droplet Combustion Experiment and the fifth run of the diffusion of molten semiconductors experiment will be initiated in the Large Isothermal Furnace.

The next scheduled Public Affairs status report will be issued at approximately 6 p.m., July 10.


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