STS-87 Mission Science Report # 15s
Thursday, December 4, 1997, 12 noon CST
The crew of the Space Shuttle Columbia is returning to Earth tomorrow with a wealth of discoveries adding to America’s storehouse of scientific and technological knowledge gleaned from a suite of state-of-the-art science experiments. Mission Manager Sherwood Anderson at NASA’s Marshall Space Flight Center in Huntsville, Ala., describes the scientific mission of the fourth U.S. Microgravity Payload (USMP-4) as “a grand success.”
The direct benefits of this research are two-fold: “We already have two products to show for this research,” said Anderson. “The first is improved mathematical models and theories. The second is graduate students — vital members of the science teams — who will take this knowledge into industries. From the latest theories, and scientists who fully understand them, come tomorrow’s new products.”
The greatest value of this research, however, is the foundation it builds for the future. “It is pure research, the benefits of which will be a gift to our children and grandchildren, just as transistors and lasers were gifts to us from our fathers and grandfathers,” said Anderson.
For science teams on the ground, the mission is just the beginning of months of research and discovery. “We’re coming home rich,” said Mission Scientist Dr. Peter Curreri. “I believe all the scientists will take home more results than anticipated. In many areas, we uncovered parts of nature masked by the effects of gravity on Earth and found new phenomena. We have an improved fundamental understanding of industrial processes that will be used to build better products, such as semiconductors for computers, infrared detectors and metals and alloys used in the airplane and automobile industries.”
Isothermal Dendritic Growth Experiment Highlights: Fastest dendritic growth rate ever measured and highest level of undercooling ever obtained for pivalic acid sample
The science team investigating the growth of dendrites — tiny, tree-like structures which form as liquid metals solidify -- is taking full advantage of the last few hours of the mission to continue its research, which has already yielded new scientific information.
From its remote “telescience” location at Rensselaer Polytechnic Institute in Troy, N.Y., researchers witnessed the fastest dendritic growth rate ever measured for pivalic acid, a transparent material used by the researchers to model metals. “The sample crystallized at a rate of 875 micrometers per second -- faster than ever before achieved with this substance,” said investigator Dr. Martin Glicksman of the Rensselaer Polytechnic Institute. “To do this, we had to establish a supercooling temperature of 2.25 degrees Fahrenheit — the largest supercooling ever obtained with this material on Earth or in space.” Supercooling occurs when a liquid is cooled below its freezing point, yet remains a liquid.
Researchers have recorded information about the growth of dendrites almost non-stop while Columbia has been in orbit. “This — the ‘virtual laboratory’ — is a preview of science operations on the International Space Station,” said investigator Dr. Matthew Koss of Rensselaer Polytechnic Institute. “It will enable the continuation and advancement of quality microgravity research like that conducted on USMP-4.”
On Earth, gravity greatly affects the size, shape and orientation of dendrites as they grow. Crystals grown during the mission in the low-gravity environment of space have already provided researchers with “extremely valuable” insight into dendrite formation.
Findings from the investigation may lead to new techniques for industrial processing of metal alloys on Earth and in turn, lead to stronger, longer-lasting materials, such as steel, aluminum and superalloys used in the production of automobiles and airplanes.
Confined Helium Experiment Highlight: Most precise temperature measurement ever made in space
In a fundamental physics experiment, a study of the behavior and properties of materials, the most precise measurement of temperature ever recorded in space was produced. During the experiment, cooled, liquid helium — a material that conducts heat 1,000 times more efficiently than any other — was “squeezed” between very flat plates until it became two- dimensional. Then, precise temperature measurements were taken. On Earth, under the influence of gravity, the temperature varies throughout the sample, but in space, the temperature is spread evenly throughout the sample, which allowed these very precise measurements to be taken.
Scientists achieved a temperature measurement to a precision of about one-tenth-of-a- billionth of a degree Kelvin. To put that measurement into understandable perspective, the temperature resolution of one-tenth-of-one-billion of 1 degree is equivalent to the ability to measure the distance between Los Angeles and New York to the thickness of a fingernail.
The investigation, led by Dr. John Lipa of Stanford University in Stanford, Calif., is designed to reveal how electrons might flow through thinner channels etched into computer chips, increasing their capacity for high-speed electronic operations. “We are studying the novel properties of matter when it becomes very thin,” said Dr. Talso Chui, a co- investigator from the Jet Propulsion Laboratory in Pasadena, Calif. The flight experiment collected information not possible to collect from the ground, and may have a direct impact on the world’s computer industry and the design of thinner, smaller computer chips for tomorrow’s computers.
MEPHISTO (Materials for the Study of Interesting Phenomena of Solidification on Earth and In Orbit Experiment) Highlight: For the first time, researchers separate two processes of solidification and measure the speed of smooth crystal growth
For the first time — in the low-gravity environment of space — the MEPHISTO team observed two separate processes of solidification. Results have shown that solidification occurs slightly below the melting point of a material and depends upon the material composition and how atoms from the liquid material attach themselves to the forming solid.
“The information obtained is excellent,” said the experiment’s lead investigator, Dr. Reza Abbaschian of the University of Florida in Gainesville, Fla. Early in the mission, following the first two measurements, the science team reported unexpected results. “The crystal growth velocity for growing smooth crystals was expected to be about 1 inch per hour,” said Abbaschian, “but we saw the smooth crystal growth at one-quarter inch per hour. This unexpected result permits science to critically examine existing theories and modify theoretical models based on MEPHISTO results.”
This is a joint experiment between NASA, the French Space Agency, and Australian researchers — all working together to gather information about the effect of temperature on the growth rate and quality of semiconductor crystals. Ultimately, this study is expected to markedly improve the production processes for making products ranging from alloys for airplane turbine blades to electronic materials.
For the study, researchers melted and solidified samples of metal bismuth, with small additions of tin, in a furnace known as MEPHISTO — a French acronym for Materials for the Study of Interesting Phenomena of Solidification on Earth and In Orbit. Bismuth has similar properties to silicon — an element used to make computer chips. But it melts at a lower temperature than silicon, making it better suited for experiments in the furnace facility aboard Columbia. As the samples solidified, the science team recorded and mapped the changes which occurred in the interface, or the point where liquid meets solid.
Advanced Automated Directional Solidification Furnace Lead-Tin-Telluride Highlight: Low- and high-temperature crystals produced to analyze new structures and new processing procedures
In a second furnace onboard Columbia, additional studies were conducted to study the solidification of metals. The Advanced Automated Directional Solidification Furnace, with its precise temperature control, allowed growth of large, near-perfect crystals of various types of semiconductor materials.
The first investigation involved melting and solidifying three samples of lead-tin-telluride crystals. “We completed processing one sample in both the low-temperature and high- temperature modes of operation,” said Dr. Archibald L. Fripp Jr., one of the experiment’s principal investigators from NASA’s Langley Research Center in Hampton, Va. “The low- temperature sample looked at thermal convection or flows, and the high-temperature sample studied the changes caused by manipulating the growth rate of the crystal.”
The flows and composition of these crystals determine the speed and amount of information stored and sent by computer and high-tech electronics. From this investigation, researchers hope to learn processes to improve crystal structure and performance and to reduce production costs. Analysis of the crystals will be performed after the samples are returned to Earth.
Experiment operations in the furnace ended earlier than planned on mission day 12 when the science team noted unexpected readings from several of the facility’s temperature sensors used to control the solidification of samples. The furnace was cooled down before the second group of three lead-tin-telluride samples were processed in the facility.
“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.”
Advanced Automated Directional Solidification Furnace Mercury-Cadmium-Telluride Highlight: Produced exceptionally uniform crystal expected to have unique capabilities
For nearly 70 hours, beginning on day six of the mission, a sensitive investigation of the solidification of mercury-cadmium-telluride crystals was conducted in the Advanced Solidification Furnace. The Growth of Solid Solution Single Crystal experiment produced a single, unique electrical crystal with exceptional uniformity of composition.
“We could only get this uniformity in the microgravity of space,” said investigator Dr. Donald C. Gillies of NASA’s Marshall Space Flight Center in Huntsville, Ala. “One of our objectives on this flight was to get benchmarks — near-perfect materials that can be used to compare with and judge materials made on Earth,” said lead researcher Dr. Sandor Lehoczky of the Marshall Center. And, Marshall investigator Dr. Dale Watring added: “We’re working on the materials for the future. With the study of the ‘mer-cad-telluride’ alloy in its infancy, we’ve only begun to scratch the surface of what could be possible.”
Following the mission, the crystal will be polished and etched. Researchers believe the space-grown crystal may be able to detect previously undetectable infrared energy levels.
Wetting Characteristics of Immiscibles Experiment Highlight: For the first time, the “wetting” mixing process is observed and recorded
In the Microgravity Glovebox, a contained workplace for hazardous material, experiment operations began early in the mission with a study of wetting — or coating along the container wall — that prevents some liquid metals from mixing well. During USMP-4, researchers were able to observe and record this process for the first time. In the past when such metals are processed on Earth, gravity caused the liquids to separate like oil and water. Developing a method to eliminate the separation will improve the uniformity and, in turn, the strength of materials.
“The flight results were fantastic, exactly what we wanted to see,” said lead investigator Dr. Barry Andrews of the University of Alabama at Birmingham, Ala. The first two experiment runs set the pace, yielding “fascinating” information. “The samples indicated a natural tendency toward wetting. This result was completely unexpected and will provide substantial information on the importance of wetting tendencies,” said Andrews. “We’ve learned that the extent of the materials’ separation depends on the container and different temperature phases.” Results from the experiment may lead to improved materials on Earth ranging from simple ball bearings to complex semiconductors.
Particle Engulfment and Pushing by a Solid/Liquid Interface Experiment Highlight: First-ever observation of the pushing of large agglomerates of particles
Another experiment performed in the Glovebox facility, called the Particle Engulfment and Pushing by a Solid/Liquid Interface, examined the solidification of liquid metals alloys. “We saw — for the first time — large clusters of particles being pushed,” said lead investigator Dr. Doru Stefanescu of the University of Alabama in Tuscaloosa, Ala.
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, but uneven distribution results in a weakened material. “We haven’t seen that on Earth. This confirms our theoretical predictions that the critical velocity, or the velocity at which particles are engulfed rather than pushed, is lower on Earth.”
Added Stefanescu: “We learned that our theory about the size of the particle groupings doesn’t drive engulfment, rather convection flow or sedimentation caused by gravity greatly affects the engulfment of particles or impurities.” Stefanescu said the theoretical models addressing the engulfment of large groupings of particles needs to be revamped to better reflect the effect gravity has on particles, and the effect particles have on composite strength and stability.
Findings from this investigation may lead to improved techniques for processing metal alloys on Earth, resulting in stronger, lighter materials for use in the auto and aerospace industries. It may also provide an understanding of how and why pot holes form on road surfaces and how to prevent them.
Enclosed Laminar Flames Experiment Highlight: First probability chart for flame stabilization in microgravity established
The mission’s only combustion science experiment, a study of flame stabilization under varying fuel and air flows, allowed researchers to chart the first probability curve of flame stabilization. The Enclosed Laminar Flames investigation studied laminar gas flows — a key phenomenon in combustion processes, such as those used to power jet engines of aircraft, natural gas power plants and some modern ships. Researchers sought to gain a better understanding of why jet engines occasionally flame-out, which occurs when fuel injected into a moving airflow moves out of the combustion chamber and extinguishes.
In the experiment, a flame was ignited in a controlled air flow inside the glovebox facility. The science team on Earth recorded when the flame lifted from the burner and under what conditions the flame extinguished. “We hypothesized that flames would remain stable at a higher forced air flow in the microgravity environment, and that’s exactly what we saw,” said investigator Dennis Stocker of NASA’s Lewis Research Center in Cleveland, Ohio.
“This research will have direct bearing on engine safety and furnace efficiency,” said researcher Dr. Lea-Der Chen of the University of Iowa in Iowa City. “This data will also allow us to critically test our computer simulations by comparing them to the data we received from the experiment.”
Space Acceleration Measurement System Orbital Acceleration Research Experiment Highlight: Researchers track vibration disturbances and effects on sensitive experiments
Throughout the mission, a team known as the Principal Investigators’ Microgravity Services group continually worked to provide science teams with important information about the ever-so-slight, yet avoidable disturbances in the Shuttle’s microgravity environment.
Highly sensitive instruments, called accelerometers, recorded accelerations, movements and vibrations aboard Columbia. The accelerometers include the Space Acceleration Measurement System and the Orbital Acceleration Research Experiment. “They measure the vibrations that occur on the Shuttle,” explained the group’s project scientist, Melissa Rogers of NASA’s Lewis Research Center in Cleveland, Ohio. “The vibrations — which are a lot like earthquake tremors — stem from a variety of things. Some are caused by operation of equipment, such as fans, pumps or thruster firings. Even exercise on bicycles by the crew causes vibration.”
Even the slightest vibration can affect the results of sensitive science experiments. Rogers and her team continually analyzed information from the accelerometers and distributed it to all the mission’s science teams. “If we can identify what’s causing a disturbance to an experiment,’’ said Rogers, “a science team can then decide whether to ask for that interfering fan, pump or whatever to be turned off — if it’s not critical.”
Video Guidance Sensor Flight Experiment Highlight: Sensor tracks and measures satellite positions
In an experiment not directly related to USMP-4, the “eyes” of a system that could allow NASA spacecraft to automatically link up in orbit was tested during the mission. The investigation team, led by Dallias Pearson of the Marshall Center, received its first information from the Automated Rendezvous and Capture Video Guidance Sensor Flight Experiment during deployment of the Spartan 201-04 satellite on day three of the mission. It was cut short when problems with Spartan necessitated a spacewalk to retrieve the satellite, but the crew successfully completed the experiment early Wednesday morning.
During the experiment, Pilot Steven Lindsey raised the Spartan satellite on the robotic arm from the Shuttle’s cargo bay. The laser sensors — located in the cargo bay — were directed at a target on the satellite. As the satellite was moved to various positions, the sensors tracked the target, measuring distance and angles to it.
“This research opens doors for new investigations,” said Curreri. “This series of USMP-4 flights has been enabling for what we will do in the future. My thoughts are already on pursuing concepts for experiments to be conducted aboard the International Space Station.”
The STS-87 mission concludes with the scheduled landing of Columbia set for 6:23 a.m. CST Firday at the Kennedy Space Center
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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