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Microgravity Science Space Flights 3

 

CONTENTS
Life and Microgravity Spacelab, June 1996
Shuttle/Mir Science Program, March 1995 to May 1998
Future Directions

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.

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.


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.

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

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.

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.

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.

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.

To reach the next level of understanding 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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