Science operations of the fourth U.S. Microgravity Payload are winding up today aboard the Space Shuttle Columbia as the focus of the STS-87 mission turns to preparing for Columbia’s return to Earth and scheduled landing at 6:23 a.m. CST Friday. And, late Tuesday night an experiment was completed to test the “eyes” of an automated rendezvous and capture system that would allow spacecraft to automatically link up in orbit.
The last measurements on samples by the MEPHISTO furnace science team were taken Tuesday in its study of the melting and solidification of a metallic alloy consisting of bismuth and tin. Since day two of the mission, researchers have been gathering information about the influence of temperature on the growth rate and quality of semiconductor crystals.
“The performance of the hardware and samples, and the quality of data received were superb through the entire mission,” said lead investigator Dr. Reza Abbaschian of the University of Florida in Gainesville.
Following the last measurements, the samples were quenched -- or rapidly cooled -- to preserve their final composition for further analysis on the ground. “Intense analysis of the data will continue for six months to a year,” said investigator Kirk Beatty of the University of Florida at Gainesville. “A lot will depend on the structure and composition of the samples, which will help in analyzing the data.”
From the experiment, researchers hope to improve the structure of semiconductor crystals to enhance their performance in electronic products such as computers and infrared detectors. Semiconductor materials have made possible the electronic revolution that has occurred during the second half of the 20th Century, and they continue to be the focus of intensive effort to enhance their capabilities.
Meanwhile, in another materials investigation aboard Columbia, the science team studying the growth of dendrites -- tiny tree-like structures that form in metal alloys as they solidify -- continues to add to their extensive harvest of information.
“The data from the experiment indicates that we have obtained the science we desired and that the post-flight analysis will be productive and rewarding,” said lead investigator Dr. Matthew Koss, with Rensselaer Polytechnic Institute in Troy, N.Y.
Most liquid metals solidify by forming dendrites, which expand throughout the material until it is completely solid. In Earth’s gravity, dendrites do not grow evenly throughout the material. They can settle at the bottom or shrink, leaving areas void of dendrites and weakening the material. The primary field of application for results of this study is the metal casting industry, for improving the quality and ability to predict the performance of materials.
Overnight, the crew successfully completed an experiment to test the video and laser sensors for an Automated Rendezvous and Capture capability -- or an automated in-orbit spacecraft docking system. The Video Guidance Sensor team, led by Gene Beam of NASA’s Marshall Space Flight Center in Huntsville, Ala., earlier in the mission saw their experiment cut short when problems with Spartan necessitated a spacewalk to retrieve the satellite.
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, consisting of small, specially shaped mirrors. As the satellite was moved to various positions, the sensors tracked the target, measuring distance and angles to the target.
Ahead, during the final hours of USMP-4 operations, the Dendritic Growth Experiment will continue.
The final Public Affairs status report will be issued at approximately noon, Thursday, Dec. 4. 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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