From: ISS Science Operations News
Posted: Friday, September 13, 2002
Flight Engineer Peggy Whitson completed the final three sample runs of a semiconductor materials experiment during the past week aboard the International Space Station.
Whitson installed and activated the sixth sample Sept. 4 in the Solidification Using a Baffle in Sealed Ampoules (SUBSA) experiment.† On Saturday, she installed and started the seventh sample run of the Expedition and removed it Sunday after completing a normal 15-hour heating and cool-down cycle.† On Tuesday, Whitson installed and initiated the eighth and final sample run of Expedition Five.†† She is scheduled to remove the sample today.† The experiment was conducted in the Microgravity Science Glovebox facility in the Destiny laboratory module.†
SUBSA examines the solidification of semiconductor crystals from a melted material.† For this investigation, tellurium and zinc known as dopants are added to molten indium antimonide specimens that are then cooled to form a single solid crystal.† Uniform distribution of the tellurium and zinc are important in controlling the opto-electronic properties of the semiconductors.† In the low gravity environment of the Station convection-driven fluid motion in the molten material is substantially reduced, giving scientists a better look at residual non-convective fluid transport during semiconductor material formation. The goal of SUBSA is to identify what causes the non-convective motion in melted materials processed in space and to reduce the magnitude of the motion so that more homogenous distribution of the dopants is achieved in the solidified crystal.
ìI would say our first Glovebox experiment has been very successful,î said SUBSA Project Scientist Dr. Martin Volz, of NASAís Marshall Space Flight Center in Huntsville, Al. "Itís safe to say it's the first time in space that anybody has actually seen the processing of a semiconductor. Earlier space experiments were done in metal cartridges, while ours were done in clear quartz sample tubes, while we watched on video from the ground. It helped us figure out how hot we needed to get the furnace to melt just the right amount of semiconductor seed material. Without it, we would have had to rely on sensors that were not as accurate. The video has enabled us to see the real growth rate of the sample, whether it's constant and whether microgravity affects the growth rate."
The samples will be stored onboard for return on a future Space Shuttle mission, Volz said. Some initial x-ray analysis will be conducted at NASA's Kennedy Space Center, a short distance from the Shuttle landing strip before the samples are returned to Principle Investigator Dr. Aleksandar Ostrogorsky, of Rensselaer Polytechnic Institute, Troy, N.Y., for more detailed study.
Volz added that the Glovebox also proved itself in supporting Station research.
"These kinds of experiments that involve potential hazards to the crew or the Station wouldn't have been possible without the high level of containment and safety provided by the Microgravity Science Glovebox," he said.
Also today (Wednesday), Whitson will begin onboard familiarization and setup for the Pore Formation and Mobility Investigation (PFMI) in the Glovebox. She will install the new experiment today.. After reconfiguring the Glovebox for the new experiment and conducting a series of checkout tests, including a non-sample test run commanded from the ground, the crew is expected to begin the first PFMI tests on Sept. 17 and
Sept. 19. PFMI also uses a furnace to process materials. It will melt and resolidify samples of a transparent modeling material, succinonitrile and succonontrile water mixtures, to observe how bubbles form in the samples and study their movement. Bubbles that become trapped in metals or crystals can form defects that decrease the material's strength and usefulness. Scientists hope to gain insights that will improve solidification processing in a microgravity environment and similar processes on Earth.
On Saturday, the crew took documentation photos of the Advanced Astroculture experiment. This commercial experiment is growing soybean plants during Expedition Five to determine if the space-grown plants produce seeds with unique chemical composition that could be beneficial to agriculture.
On Monday, the crew conducted the regular monthly session with the Pulmonary Function in Flight (PuFF) experiment. This ongoing research focuses on lung function both inside the station and following spacewalks.
On Thursday, the crew is scheduled to conduct a 21-day pre-spacewalk background radiation check with the EVA Radiation Monitoring (EVARM) experiment, which records radiation levels received by specific parts of the human body inside the Space Station and during spacewalks outside the Station.
On Friday, selected members of the crew are scheduled to participate in the Crew Interactions experiment. Based on the results of the weekly surveys of both Station crews and ground teams, the study will examine issues involving tension, cohesion and leadership roles in the crew in orbit and in the ground support crews.
Photography subjects for the Crew Earth Observations project this week included: Perth, Australia, landslides in the Cornish moors of the United Kingdom, Damascus, Syria, Saharan dust along the Libiyan and Tunisian coastlines, Barcelona, Space, Puerto Rico, St. Coix, the lower Amazon River basin, the Pilcomayo swamplands in Paraguay and Argentina, and Necker Island in the Hawaiian chain.
Automated experiments involving biological materials, space construction materials, the station's vibration environment, and plant growth continued to function well aboard the Station, while liver cell, petroleum processing and drug delivery experiments have been completed and are stored for return to scientists on Earth. The crew continued its daily payload status checks to make sure that all experiments and payload facilities continue to operate properly.
Editor's Note: The Payload Operations Center at NASA's Marshall Space Flight Center in Huntsville, Ala., manages all science research experiment operations aboard the International Space Station. The center is also home for coordination of the mission-planning work of a variety of international sources, all science payload deliveries and retrieval, and payload training and payload safety programs for the Station crew and all ground personnel.
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