ISS Science Operations Status Report for week ending August 14, 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.
