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Microgravity Science Space Flights 2

CONTENTS
International Microgravity Laboratory-2, July 1994
United States Microgravity Laboratory-2, October 1995
United States Microgravity Payload-3, February 1996

International Microgravity Laboratory-2, July 1994

The second International Microgravity Laboratory (IML-2), with a payload of 82 major experiments, flew in July 1994 on the longest Space Shuttle flight to that time. IML-2 truly was a world class venture, representing the work of scientists from the U.S. and 12 other countries.

Materials science experiments focused on various types of metals processing. One was sintering, a process that can combine different metals by applying heat and pressure to them. A series of three sintering experiments expanded the use in space of the Japanese built Large Isothermal Furnace, first flown on SL-J. It successfully sintered alloys of nickel, iron, and tungsten.

Other experiments explored the capabilities of a German-built facility called TEMPUS. It was designed to position molten metal experiment samples (molten drops) away from the surfaces of a container in order to eliminate processing side effects of containers. Experiments of four U.S. scientists were successfully completed, and the research team developed improved procedures for managing multi-user facilities.

One of the experiments used a clever approach to measure two important thermophysical properties of molten metals. While a spherical drop of molten metal was positioned in a containerless manner it was momentarily distorted by using electromagnetic forces to squeeze it. When the squeezing was released, the droplet began to oscillate. The surface tension of the molten metal was determined from the frequency of the oscillation. The oscillation gradually decayed. The rate at which the decay occurred was used to determine the viscosity of the molten material.

Biotechnology experiments were performed using the Advanced Protein Crystallization Facility, developed by the European Space Agency. The facility's 48 growth chambers operated unattended throughout the flight, producing high-quality crystals of nine proteins. High-resolution video cameras monitored critical

 
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Representations of different shapes of the liquid-solid interface in a solidifying material: a) planar, b) cellular; and c) dendritic. More information about interface morphology is provided in the Metals and Alloys discussion in the Materials Science section of this site.
crystal growth experiments, providing the research team with a visual record of the processes. U.S. investigators used the Bubble, Drop, and Particle Unit to study how temperature gradients in the liquids influence the movement and shape of gas bubbles and liquid drops. The Critical Point Facility enabled researchers to study how a fluid behaves at its critical point. Research using the Critical Point Facility is applicable to a broad range of scientific questions, including how various characteristics of solids change under different experimental conditions.

United States Microgravity Laboratory-2, October 1995

The second United States Microgravity Laboratory (USML-2) launched on October 20, 1995 for a mission with more than 16 days on orbit. During that time microgravity research was conducted around-the-clock in the areas of biotechnology, combustion science, fluid physics, and materials science. It was a perfect example of interactive science in a unique laboratory environment.

Along with investigations that previously flew on USML-1, several additional experiment facilities flew on USML-2. Fourteen protein crystal growth experiments in the Advanced Protein Crystallization Facility had varied results that provided more insight into the structures of some of the proteins and into optimal experiment conditions. The goal of the Geophysical Fluid Flow Cell experiment was to study how fluids move in microgravity as a means of understanding fluid flow in oceans, atmospheres, planets, and stars. The results of the studies of fluid movement and velocity are still being analyzed.

In the Geophysical Fluid Flow Cell, electric charges, electrostatic force, and heaters are used to simulate buoyancy forces, radial gravity, and heating patterns in planetary atmospheres. As shown in the diagram, attempts to use spherical models on Earth are hampered by the force of Earth's gravity acting perpendicular to the sphere's rotation (indicated by the large curving arrow). In microgravity, this problem is removed.

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Gravitational force acting on spherical planetary models on Earth and in a microgravity environment

Four separate studies were performed in the Crystal Growth Furnace (CGF). The goals of the experiments were to investigate quantitatively the gravitational influences on the growth and quality of the compound semiconductor, CdZnTe, using the seeded, modified Bridgman-Stockbarger crystal growth technique; to investigate techniques for uniformly distributing a dopant, selenium, during the growth of GaAs crystals; to understand the initial phase of the process of vapor crystal growth of complex, alloy-type semiconductors (HgCdTe); and to test the integration of a current induced interface demarcation capability into the CGF system and to assess the influences of a change in Shuttle attitude on a steady-state growth system using the demonstrated capabilities of the interface demarcation technique. Earth Environment Microgravity Environment Force of Earth's Gravity Experimental Sphere Force of Radial Gravity Experimental Sphere Gravitational force acting on spherical planetary models on Earth and in a microgravity environment

Two investigators had experiments conducted in the Drop Physics Module. The Science and Technology of Surface-Controlled Phenomena Experiments had three major goals: to determine the surface properties of liquids in the presence of surfactants; to investigate the dynamic behavior and the coalescence of droplets coated with surfactant materials; and to study the interactions between droplets and acoustic waves. The shapes of oscillating drops recorded on videotape were analyzed frame by frame, revealing the variations of the oscillation amplitude with time. The frequency and damping constant of the droplet shape oscillations were calculated. Analysis of the results is ongoing.

The goals of the Drop Dynamics Experiment were to gather high-quality data on the dynamics of liquid drops in microgravity for comparison with theoretical predictions and to provide scientific and technical information needed for the development of new fields, such as containerless processing of materials and polymer encapsulation of living cells. The experiments on the USML-2 mission included breaking one drop into two drops (bifurcation) and positioning a drop of one liquid at the center of a drop of a different liquid. Preliminary results show that the acoustic levitation technique has a strong influence on the drop bifurcation process.

Seven investigations were performed in the Glovebox on USML-2. These studies examined various aspects of fluid behavior, combustion, and crystal growth. Two separate devices were used for protein crystal growth experiments.

The Surface Tension Driven Convection Experiment investigated the basic fluid mechanics and heat transfer of thermocapillary flows generated by temperature variations along free surfaces of liquids in microgravity. It determined when and how oscillating flows were created. Preliminary analysis indicates that current theoretical models used to predict the onset of oscillations are consistent with the experiment results.

The USML-2 Zeolite Crystal Growth experiment attempted to establish a quantitative understanding of zeolite crystallization to allow control of both crystal defect concentration and crystallite size. The preliminary conclusions indicate that, with few exceptions, the crystals from USML-2 are larger in size than their Earth-grown counterparts and are twice as large as those grown on previous Shuttle flights. Analysis will continue to determine the effect of space processing on crystal defect concentration.

The projects that measured the microgravity environment added to the success of the mission by providing a complete picture of the Shuttle's environment and its disturbances. The Orbital Acceleration Research Experiment (OARE) provided real-time quasi-steady acceleration data to the science teams. The Microgravity Analysis Workstation (MAWS) operated closely with the OARE instrument, comparing the environment models produced by the MAWS with the actual data gathered by the OARE. Two other instruments, the Space Acceleration Measurement System and the Three Dimensional Microgravity Accelerometer, took g-jitter measurements throughout the mission. The Suppression of Transient Events by Levitation demonstrated a vibration isolation technology that may be suitable for experiments that are sensitive to variations in the microgravity environment.

 
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The change in acceleration character seen in the middle of this plot is due to a crew member swinging an experiment container around to mix its contents. Examination of the plot indicates that the crew member swung his arm around seven to eight times in ten seconds.

Vibration Frequencies Commonly Seen in Orbiter Accelerometer Data
 Freq. (Hz)  Disturbance Source
 0.43  cargo bay doors
 3.5  Orbiter fuselage torsio
 3.66  structural frequency of Orbiter
 4.64  structural frequency of Orbiter
 5.2  Orbiter fuselage normal bending
 7.4  Orbiter fuselage lateral bending
 17  Ku band antenna dither
 20  experiment air circulation fan
 22  refrigerator freezer compressor
 38  experiment air circulation fan
 39.8  experiment centrifuge rotation speed
 43  experiment air circulation fan
 48  experiment air circulation fan
 53  experiment air circulation fan
 60  refrigerator piston compressor
 80  experiment water pump
 166.7  Orbiter hydraulic circulation pump


United States Microgravity Payload-3, February 1996

The third United States Microgravity Payload mission launched on February 22 for 16 days of research on orbit. During that time, microgravity research was conducted in the areas of combustion science, fluid physics, and materials science. The ultimate benefit of USMP-3 research will be improvements in products manufactured on Earth. During the eight and one-half days dedicated to microgravity science, researchers used telescience to control materials processing and thermodynamic experiments in the Cargo Bay and astronauts performed combustion studies in the Middeck Glovebox.

The MEPHISTO science team used flight-proven equipment to learn how the chemical composition of solidifying Sn-Bi alloys changes, and can be controlled, during solidification. Such knowledge applies to ground-based materials processing. For the first time, the changes in the microgravity environment caused by carefully planned Shuttle thruster firings were correlated with the effects of fluid flows in a growing crystal. With the help of data from the Space Acceleration Measurement System, the experiment data showed that with thruster accelerations parallel to the crystal-melt interface a large effect was noted, whereas when thruster accelerations were perpendicular to the interface there was little impact. Also, the MEPHISTO team successfully monitored the point at which their sample's crystal interface underwent a key change-from flat to cellular (like three dimensional ripples)-as it solidified. Measurements from the MEPHISTO facility will now be analyzed, along with the final metallic samples, in order to increase our understanding of subtle changes that occurred during the samples' solidification and subsequent cooling.  
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As the ISS era approaches, more experiment monitoring and control is being performed from NASA centers and university laboratories "remote" from Marshall and Johnson Space Centers.

In the Advanced Automated Directional Solidification Furnace, three lead tin telluride (PbSnTe) crystals were grown while Columbia orbited in three different attitudes, to determine how these orientations affect crystal growth. This knowledge is expected to help researchers develop processes, and semiconductor materials that perform better and cost less to produce.

The Isothermal Dendritic Growth Experiment (IDGE) on USMP-3 achieved its mission objectives. After collecting data to answer some of the questions opened by the USMP-2 results, research has shown that the small variations in dendritic growth rates (how fast the tree-like solid pattern in a molten metal forms) measured in microgravity on the Space Shuttle are not due to variations in the microgravity environment on orbit. The investigators are currently completing measurements on the three-dimensional shape of these dendritic tips, which will further advance the empirical basis from which more accurate solidification models are being developed and tested. This is an early step in what will ultimately be solidification models that could be used to make less expensive and more reliable cast or welded metal and alloy products.

The IDGE team also participated in an important technology demonstration by commanding a microgravity space instrument from a remote site located at the Rensselaer Polytechnic Institute. This first-ever remote commanding to the Shuttle from a U.S. university campus foreshadows operations aboard the International Space Station.

Investigators for the Critical Fluid Light Scattering Experiment were successful in observing, with unprecedented clarity, xenon's critical point behavior-the precise temperature and pressure at which it exists as both a gas and a liquid. The transparent xenon sample displayed the unusual critical point condition, with maximum light scattering followed by a sudden increase in cloudiness. This effect was much more distinctive than observed during the USMP-2 mission and happened at a lower temperature than expected. Knowledge gained from this experiment will prove valuable for applications from liquid crystals to superconductors.

This mission was the first flight of a Glovebox facility in the Middeck section of the Shuttle. Three combustion science investigations were conducted by the crew. The Forced Flow Flamespreading Test burned 16 paper samples, both flat and cylindrical. Video of the cylindrical samples showed significant differences in flame size, growth rate, and color with variations in air flow speed and fuel temperature. The Comparative Soot Diagnostics investigation completed 25 combustion experiment runs. The team obtained excellent results, testing the effectiveness of two different smoke-sensing techniques, for detecting fires aboard the Shuttle and the International Space Station. The Radiative Ignition and Transition to Spread Investigation team observed new combustion phenomena, such as tunneling flames which move along a narrow path instead of fanning out from the burn site. Also, for the first time, these investigators studied the effects of sample edges and corners on fire spreading in microgravity.

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Glovebox Investigation Module hardware.

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