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Microgravity Science Space Flights 3
CONTENTS
Life and Microgravity Spacelab,
June 1996
The Life and Microgravity Spacelab mission successfully completed
a 17 day flight on July 6, 1996. For this mission there was an unprecedented
distribution of teams monitoring their experiments around the world, with
experiment commanding performed from three sites.
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A number of researchers conducted experiments using the Advanced
Gradient Heating Facility (AGHF) from the European Space Agency.
Three aluminum-indium alloys were directionally solidified to study
the physics of solidification processes in immiscible alloys called
monotectics. The three samples, which differed only in indium content,
were processed at the same growth rate to permit a comparison of
microstructures, how the indium was distributed in the aluminum
matrix. Two of these samples were of compositions which cannot be
processed under steady state conditions on Earth due to gravitationally-driven
convective instabilities and subsequent sedimentation of the liquid
indium.
Another AGHF experiment used commercial Al-based samples to obtain
insight into the mechanism of particle redistribution during solidification.
Additional studies were geared toward enhancement of the fundamental
understanding of the dynamics of insoluble particles at solid/liquid
interfaces. The physics of the problem is of direct relevance to
such areas as solidification of metal matrix composites, management
of defects such as inclusions and porosity in metal castings, development
of high temperature superconductor crystals with superior current
carrying capacity, and the solidification of monotectics.
A series of experiments was performed in the Advanced Protein Crystallization
Facility. The experiments were generally successful in terms of
yielding crystals. Those crystals which showed particular promise,
based on early microscopic examination, were ferritin, satellite
tobacco mosaic virus, satellite panicum mosaic virus, Iysozyme,
and canavalin.
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The Space Shuttle Columbia, carrying the Life and
Microgravity Spacelab, launched from Kennedy Space Center June 20,
1996.
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Several experiments were conducted using the Bubble, Drop and Particle
Unit (BDPU) from the European Space Agency. In one experiment, the
transition to periodic and chaotic convection was detected. The
results of this experiment will trigger ground based research on
the nonlinear dynamics of convecto-diffusive systems. In another
experiment, thermocapillary flows in two and three layer systems
were observed for five temperature gradients. The results of this
experiment will improve our understanding of heat and mass transfer
in other fluid physics research
An additional experiment studied the interaction between pre-formed
gas bubbles inside a solid and a moving solid/liquid interface,
obtained by heating an initially solid sample. Early results concerning
the release of bubbles from the melting front indicate that once
a hole has been made and the gas inside the bubble contacts the
liquid then the liquid enters the cavity (by wetting the solid walls)
and pushes out the gas inside the bubble.
The scientific results of one set of BDPU experiments provide us
with new insights into bubble dynamics and into evaporation. This
will lead to a better understanding and modeling of steam generation
and boiling. Initial findings of another experiment showed that,
under microgravity conditions, boiling heat transfer is still as
efficient as under normal Earth gravity.
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Magnification of a sample of an aluminum-indium
alloy. When the sample is melted then controllably solidifies in
the AGHF; the indium forms in cylindrical fibers within a solid
aluminum matrix.
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In contrast to the existing theory the findings show that the influence
of Earth gravity is less than predicted. The heat transfer in a microgravity
environment is still as efficient, sometimes even more efficient than, at
normal gravity.
Real-time Orbital Acceleration Research Experiment data were used by
the science teams to monitor the microgravity environment during their
experiment operations. The effects of mission activities, such as venting
of unneeded water and Orbiter orientation changes, were presented to help
the science teams understand the environment in which their experiments
operated. The Microgravity Measurement Assembly (MMA) used this mission
to verify a new system, augmented by a newly developed accelerometer for
measuring the quasi-steady range. MMA provided real-time quasi-steady
and g-jitter data to the science teams during the mission.
Shuttle/Mir Science Program,
March 1995 to May 1998
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Although competition in the space program has existed between the
United States and Russia for some time, there has also been a rich
history of cooperation that has grown into the highly successful
joint science program that it is today. One part of that program
is geared towards microgravity research.
Many of the investigations from that program are configured to
run in a Glovebox facility that has been installed in the Priroda
research module of the Mir Space Station. The Microgravity Isolation
Mount (MIM) is also located in Priroda. The MIM was developed by
the Canadian Space Agency to isolate experiments attached to it
from ongoing g-jitter. The MIM is also able to induce defined vibrations
so that the effects of specific disturbances on experiments can
be studied. Additional experiments are being performed in individual
experiment facilities that have been placed in the Priroda and other
Mir modules.
Various protein crystal growth experiments use the Gaseous Nitrogen
Dewar (GN2 Dewar). Samples are placed in the GN2 Dewar and it is
charged with liquid nitrogen, freezing them. The system is designed
so that the life of the nitrogen charge lasts long enough to get
the payload launched and into orbit. As the system absorbs heat,
the nitrogen boils away and the chamber approaches ambient temperature.
As the samples thaw, crystals start growing in the Dewar. The crystals
are allowed to form throughout the long duration mission and are
returned to Earth for analysis. Initial investigations using the
Dewar served as a proof of concept for the experiment facility.
Successive experiment runs using different samples will continue
to improve our knowledge of protein crystal structures.
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Schematic diagram of Space Shuttle Orbiter
docked to Mir.
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The Diffusion-Controled Crystallization Apparatus for Microgravity
experiment is designed primarily for the growth of protein crystals
in a microgravity environment. It uses the liquid/liquid and dialysis
methods in which a precipitant solution diffuses into a bulk solution.
In the experiment, a small protein sample is covered by a semipermeable
membrane that allows the precipitant solution to pass into the protein
solution to initiate the crystallization process. Diffusion starts
on Earth as soon as the chambers are filled. However, the rate is
so slow that no appreciable change occurs before the samples reach
orbit one or two days later. Such an apparatus is ideally suited
for the long duration Mir missions.
The Cartilage in Space-Biotechnology System experiment began with
cell cultures being transported to Mir by the Shuttle in September
1996 on mission STS-79. The investigation is a test bed for the
growth, maintenance, and study of long-term on-orbit cell growth
in microgravity. The experiment investigates cell attachment patterns
and interactions among cell cultures as well as cellular growth
and the cellular role in forming functional tissue.
The Candle Flames in Microgravity investigation conducted 79 candle
tests in the Glovebox in July 1996. The experiments explored whether
wick flames (candles) can be sustained in a purely diffusive environment
or in the presence of a very slow, sub-buoyant convective flow.
An associated goal was to determine the effect of wick size and
candle size on burning rate, flame shape and color, and to study
interactions between two closely spaced diffusion flames. Preliminary
data indicate long-term survivability with evidence of spontaneous
and prolonged flame oscillations near extinction (when the candle
goes out).
The Forced Flow Flame Spreading Tests ran in the Glovebox in early
August 1996. The investigations studied flames spreading over solid
fuels in low-speed air flows in microgravity. The effects of varying
fuel thickness and flow velocity of flames spreading in a miniature
low-speed wind tunnel were observed. The data are currently being
analyzed and compared to theoretical predictions of flame spreading.
The numerical model predicted that the flame would spread at a steady
rate and would not experience changes in speed, shape, size, or
temperature.
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Protein and virus crystals grown
in the GN2 Dewar on Mir. |
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The Interface Configuration Experiment Glovebox investigation studied
how a liquid with a free surface in contact with a container behaves
in microgravity. This provides a basis for predicting the locations
and configurations of fluids with the use of mathematical models.
The data are currently being analyzed.
The Technological Evaluation of the MIM (TEM) was a technology
demonstration to determine the capabilities of the MIM. Through
observations of liquid surface oscillations, TEM evaluated the ability
of the MIM to impart controlled motions. The data are still being
analyzed. A follow-on technology demonstration (TEM-2) was transferred
to Mir in September 1996.
The Binary Colloidal Alloy Test Glovebox investigation was also
launched to Mir on STS-79 in September 1996. The objective is to
conduct fundamental studies of the formation of gels and crystals
from binary colloid mixtures.
The Angular Liquid Bridge and Opposed Flow Flame Spread Glovebox
investigations were carried to Mir by the Shuttle on mission STS-81
in early 1997. The former is an extension of previous fluid physics
investigations conducted on the Shuttle and Mir and studies the
behavior and shape of liquid bridges, liquid that spans the distance
between two solid surfaces. The objective of the latter is to extend
the understanding of the mechanisms by which flames spread, or fail
to spread, over solid fuel surfaces in the presence of an opposing
oxidizer flow.
A Space Acceleration Measurement System (SAMS) unit was launched
to Mir on a Progress rocket in August 1994. Starting in October
1994, the SAMS was used to measure and characterize the microgravity
environment of various Mir modules in support of microgravity experiments.
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The Biotechnology System-Cartilage in Space Experiment in orbit.
Top: Astronauts Carl Walz (left) and Jay Apt prepare the experiment
for transfer from the middeck of the Space Shuttle Atlantis to the
Priroda module of Mir. Bottom: Walz and Apt test the bioreactor
media for pH, carbon dioxide, and oxygen levels.
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Between October 1994 and September 1996, SAMS collected about sixty gigabytes
of acceleration data. The data have been used to identify common vibration
sources, as has been done with the Shuttles. This information has helped
experimenters plan the timing and location of their experiments. The Passive
Accelerometer System is a simple tool that is being used to estimate the
quasi-steady microgravity environment of Mir during the increment between
STS-79 and STS-81. The motion of a steel ball in a water-filled glass
tube is tracked and the distance travelled over time is used to estimate
accelerations caused by atmospheric drag and the location of the tube
with respect to Mir's center of gravity.
Vibration Frequencies Commonly Seen in Mir Accelerometer Data
| Freq. (Hz) |
Disturbance Source |
| 0.6 |
Kristall structural mode |
| 1.0 |
Kristall structural mode |
| 1.1 |
structural mode |
| 1.2 |
structural mode |
| 1.3 |
Kristall structural mode |
| 1.9 |
Kristall structural mode |
| 2.75 |
structural mode |
| 3.75 |
structural mode |
| 15 |
air quality system |
| 24.1 |
humidifier/dehumidifier |
| 30 |
air quality system harmonic |
| 41 |
fan |
| 43.5 |
fan |
| 45 |
air quality system harmonic |
| 90 |
air quality system harmonic |
| 166.6 |
gyrodyne (system used to maintain Mir orientation) |
Future Directions
Microgravity science has come a long way since the early days of space
flight when researchers realized that they might be able to take advantage
of the reduced gravity environment of orbiting spacecraft to study different
phenomena. Shuttle and Mir based experiments that study biotechnology,
combustion science, fluid physics, fundamental physics, and materials
science have opened the doors to a better understanding of many of the
basic scientific principles that drive much of what we do on Earth and
in space.
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about phenomena in a microgravity environment, we need to perform
experiments for longer periods of time, to be able to conduct a series
of experiments as is done on Earth, and to have improved environmental
conditions. The International Space Station is being developed as
a microgravity research platform. Considerable attention has been
given to the design of the station and experiment facility components
so that experiments can be performed under high-quality microgravity
conditions. The International Space Station will provide researchers
with continuous, controlled microgravity conditions for up to thirty
days at a time. (The time in between these thirty day increments is
used for vibration-intensive activities such as Shuttle dockings,
station reconfiguration, and upkeep.) This is almost twice as long
as the microgravity periods available on the Space Shuttle and there
will be a better environment than that provided by Mir. This increase
in experiment time and improvement in conditions will be conducive
to improved understanding of microgravity phenomena. |
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This illustration depicts the International Space Station in its
completed and fully operational state with elements from the United
States, Europe, Canada, Japan, and Russia. |
Continued microgravity research on the Shuttles, Mir, and on the International
Space Station will lead to, among other things, the design of improved
drugs, fire protection and detection systems, spacecraft systems, high-precision
clocks, and semiconductor materials. In addition, this research will allow
us to create outposts on the Moon where we can build habitats and research
facilities. The end result of research in microgravity and on the Moon
will be the increased knowledge base necessary for our trips to and exploration
of Mars.
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