From: ISS Science Operations News
Posted: Thursday, August 15, 2002
The Solidification Using Baffle in Sealed Ampoule (SUBSA) science team completed its fifth experiment run aboard the International Space Station last weekend.
SUBSA is investigating manufacturing processes that could yield insights into semiconductor production on Earth. Impurities, or dopants, in semiconductors are used to control the opto-electronic properties of the semiconductor crystal, and the uniform distribution of the dopant is essential to achieve the desired properties. The goal of SUBSA is to study the resulting solids formed in microgravity where the motion of dopants caused by buoyancy forces are greatly reduced, resulting in more even distribution of the dopants.
The test was the first to use an encapsulant in the sample tube. Liquid encapsulants are often used during semiconductor processing on Earth to form a thin film around the semiconductor as the semiconductor grows. This helps to prevent sticking between the sample and the container wall and results in fewer defects.
Following the 15-hour run on Saturday, Flight Engineer Peggy Whitson on Sunday noticed a crack in the quartz sample tube as she prepared to remove the sample. The tube broke as she removed it. Whitson used tweezers and other tools to remove the remaining sample tube. A small quartz piece, from the sample tube floated away but was confined in the work area of the Microgravity Science Glovebox where SUBSA furnace is housed. The Glovebox, which features a sealed work area with windows and built-in gloves, is designed to contain experiments with fluids, flames, particles and fumes that could otherwise escape into the Station environment. Controllers and the science team are drafting plans to recover the particles and resume SUBSA operations.
"We don't have a full answer yet for why this happened," said Dr. Aleksandar Ostrogorsky, SUBSA principal investigator with Rensselaer Polytechnic Institute, Troy, N.Y. During the past 2 years, we performed on ground 28 solidification experiments without the encapsulant and 2 experiments with the encapsulant, and this is the first ampoule that failed during processing. Based on the ground test statistics, the crack could be related to the encapsulant. The test itself was interesting and exciting because on video during the test we observed a relatively fast repositioning of the encapsulant and the melt. A dome-shaped free surface, which we've never seen on Earth, formed in the middle of the sample. We are studying the video and will be very interested to get this sample back for analysis."
On Tuesday and Wednesday, members of the crew continued to record their experiences for the Crew Interactions experiment, which examines interpersonal factors that can affect operations on long space missions.
On Wednesday, the crew removed depleted nutrient fluid from the Advanced Astroculture (ADVASC) experiment and refilled with fresh nutrients. ADVASC is growing soybean plants to learn whether they will produce seeds with improved oil, protein or carbohydrate content. This is the first soybean seed-to-seed experiment in space.
Coming up for Commander Valery Korzun and Whitson on Saturday will be the Pulmonary Function in Flight Experiment (PuFF). The lung function test will study whether their Friday spacewalk had any affect on their health. Korzun and Whitson conducted the regular monthly PuFF test last Friday. The low-pressure environment of a spacesuit can cause nitrogen in the blood to form bubbles. Additionally, little is known about how the lungs can be affected by long-term exposure to microgravity. PuFF measures changes in the evenness of gas exchange in the lungs and changes in respiratory muscle strength. Scientists hope to find new ways to protect the health of space travelers in the years ahead, and to gain a better understanding of the effects of gravity on the lungs on Earth.
Crew Earth Observations photography subjects this week included: fires in western Borneo, gold-mining cities near Johannesburg, South Africa, dry season fires in Angola, North African dust over the Mediterranean, islands and coastal features in the lower Amazon River basin, high central Andean Glaciers, and Lima, Peru.
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