STS-87 Mission Science Report # 12s
Monday, December 1, 1997, 7:00 a.m. CST
Early this morning, Mission Specialist Dr. Kalpana Chawla and Pilot Steven Lindsey initiated the second and final run of the mission’s only combustion experiment aboard Columbia, in the Middeck Glovebox facility. This study investigates laminar gas flow -- a key phenomenon in combustion processes, such as those used to power jet engines of aircraft, natural gas power plants and some modern ships.
The research is aimed at providing greater insight into why jet engines occasionally “flame out” -- which occurs when fuel injected into a moving airflow moves out of the combustion chamber and extinguishes.
During the experiment, a fuel mixture of 50 percent methane and 50 percent nitrogen is ignited in an airflow to study flame stabilization in varying fuel flows and air velocities. “We are adjusting the flow conditions and observing when the flame lifts from the burner and the conditions under which the flame is extinguished,” said principal investigator Lea- Der Chen with the University of Iowa in Iowa City. “During this second session of experiment runs we are increasing fuel and air flows to look at flame stabilization under new conditions.”
Information gathered from this study will be used to verify or correct computer modules which simulate the effect of air flow velocities on flame stabilization. Findings may lead to the design of more efficient power plant combustors and safer jet engines for military and civilian aircraft.
Experiment operations in the Advanced Automated Directional Solidification Furnace ended earlier than planned Sunday afternoon when the science team noted unexpected readings from several of the facility’s temperature sensors. These sensors are used to control the solidification of samples.
The furnace was cooled down before the second set of three lead-tin-telluride samples completed processing in the facility. The first set was successfully processed a week ago and a sample of mercury-cadmium-telluride completed successful processing Saturday.
“Prior to this mission the furnace was modified to allow the exchange of samples aboard the Shuttle,” said Assistant Mission Manager Jimmie Johnson. “Although we were unable to complete the third experiment run, the two we have completed will potentially yield more science from this mission than the previous two missions combined.”
The furnace, with its precise temperature control, is used to gradually grow large, near- perfect lead-tin-telluride crystals -- semiconductor materials which determine the speed and amount of information stored and sent by computers and high-tech electronics. Knowledge gained from this study may lead to better crystals for electronic applications and improved metal alloys for a variety of products on Earth.
Meanwhile, in the furnace known as MEPHISTO, researchers continued to process samples of the metal bismuth, with small additions of tin, to map the shape measurement cycles of the alloy. During the experiment, one-second electrical pulses are passed through a melted sample of the alloy as it solidifies, freezing the atoms at the interface -- or point where liquid meets solid. “Overall, we want to determine how temperature influences the rate at which the crystal can grow and the quality of that crystal,” said investigator Henry deGroh of NASA’s Lewis Research Center in Cleveland, Ohio.
Findings may lead to higher-quality semiconductors for computers. Bismuth has similar properties to silicon -- an element used to make computer chips -- but melts at a lower temperature so it is better suited for experiments in the science facility. “Faster growth of crystals means increased production of computer chips, but too fast and the quality goes down,” said deGroh. “So we want to know how fast we can grow crystals and maintain the quality.”
A run of the Particle Engulfment and Pushing experiment was initiated in the Middeck Glovebox late Sunday and ended early Monday morning. The experiment examines the solidification of liquid metal alloys. As alloys solidify, a front forms and moves through the material, pushing or engulfing particles in the mixture. An even distribution of particles is desirable for a strong material, however, uneven distribution of particles results in a weakened material. A better understanding of this process may lead to improved techniques for mixing metal alloys on Earth, resulting in stronger, lighter composite materials.
Researchers continued overnight to gather information from the Isothermal Dendritic Growth Experiment aboard Columbia. The study is examining the growth of dendrites -- tiny tree-like structures -- that form in metal alloys as they solidify. Virtually all alloys used in industrial processes solidify from a molten state by dendritic growth. Findings from this investigation may lead to improved industrial processing techniques on Earth.
The Confined Helium Experiment continued into the morning. During the experiment, helium molecules are cooled to just above absolute zero between flat plates so they become two-dimensional, and precise temperature measurements are taken. “We want to know at what point -- how thin the helium has to be -- before its properties change,” said investigator Melora Larson with NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “We’ve seen changes already as the helium transitions to this state that we couldn’t see on Earth.”
The experiment is designed to reveal how electrons might flow through thinner channels etched in computer chips. Results of this study may have a direct impact on the world’s computer industry and the design of thinner, smaller computer chips for tomorrow’s computers.
Ahead today, the combustion experiment will complete its second and final run in the Middeck Glovebox as the science teams continue to record data from the Dendritic Growth and Confined Helium experiments.
The next scheduled Public Affairs status report will be issued at approximately 7 a.m., Tuesday, Dec. 2. For more information call the Spacelab Newscenter at Marshall Space Flight Center at (205) 544-0034 or visit the web sites: For USMP-4 payload and science information: http://liftoff.msfc.nasa.gov/shuttle/usmp4/ and http://science.msfc.nasa.gov/usmp4/usmp4.htm For STS-87 information: http://www.shuttle.nasa.gov
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