Microgravity Science Space Flights 1

CONTENTS

International Microgravity Lab, January 1992	U S Microgravity Payload-1, October 1992
U S Microgravity Lab-1, June 1992	U S Microgravity Payload-2, March 1994
Spacelab-J, September 1992

Until the mid-20th century, gravity was an unavoidable aspect of research and technology. During the latter half of the century, the use of drop towers to reduce the effects of gravity became more prevalent, although the extremely short periods of time they provided (<6 seconds) severely restricted the type of research that could be performed. Initial microgravity research centered around solving space flight problems created by the reduction in gravity's effects experienced on orbit. How do you get the proper amount of fuel to a rocket engine in space or water to an astronaut on a spacewalk? The brief periods of microgravity available in drop towers at the Lewis Research Center and the Marshall Space Flight Center were sufficient to answer these basic questions and to develop the pressurized systems and other new technologies needed to cope with this new environment. But, they still were not sufficient to investigate the host of other questions that were raised by having gravity as an experimental variable.

Skylab, America's first space station.

The first long-term opportunities to explore microgravity and conduct research relatively free of the effects of gravity came during the latter stages of NASA's first great era of discovery. The Apollo program presented scientists with the chance to test ideas for using the space environment for research in materials, fluid, and life sciences. The current NASA microgravity program had its beginning in experiments conducted in the later flights of Apollo, the Apollo-Soyuz Test Project, and onboard Skylab, America's first space station.

Preliminary microgravity experiments conducted during the 1970's were severely constrained, either by the relatively low power levels and space available on the Apollo spacecraft, or by the low number of flight opportunities provided to Skylab. These experiments, as simple as they were, provided new insights into the roles of fluid and heat flows in materials processing Much of our understanding of the physics underlying semiconductor crystal growth, for example, can be traced back to research initiated on Skylab.

Since the early 1980's, NASA has sent crews and payloads into orbit on board the Space Shuttle. The Space Shuttle has given microgravity scientists an opportunity to bring their experiments to low-Earth orbit on a more regular basis. The Shuttle introduced significant new capabilities for microgravity research: larger, scientifically trained crews; a major increase in payload volume and mass and available power; and the return to Earth of all instruments, samples, and data. The Spacelab module, developed for the Shuttle by the European Space Agency, gives researchers a laboratory with enough power and volume to conduct a limited range of sophisticated microgravity experiments in space.

Use of the Shuttle for microgravity research began in 1982, on its third flight, and continues today on many missions. In fact, most Shuttle missions that aren't dedicated to microgravity research do carry microgravity experiments as secondary payloads. The Spacelab-1 mission was launched in November 1983. The primary purpose of the mission was to test the operations of the complex Spacelab and its subsystems. The 71 microgravity experiments, conducted using instruments from the European Space Agency, produced many interesting and provocative results. One investigator used the travelling heater method to grow a crystal of gallium antimonide doped with tellurium (a compound useful for making electronic devices). Due to the absence of gravity-driven convection, the space-grown crystal had a far more uniform distribution of tellurium than could be achieved on Earth. A second investigator used molten tin to study diffusion in low gravity- research that can improve our understanding of the solidification of molten metals.

The Spacelab module in the Orbiter Cargo Bay.

Another Shuttle mission using the Spacelab module was Spacelab-3, which flew in April 1985. SL-3 was the first mission to include U.S. developed microgravity research instruments in the Spacelab. One of these instruments supported an experiment to study the growth of crystals of mercury iodide-a material of significant interest for use as a sensitive detector of X-rays and gamma rays. Grown at a high rate for a relatively short time, the resulting crystal was as good as the best crystal grown in the Earth-based laboratory. Another U.S. experiment consisted of a series of tests on fluid behavior using a spherical test cell. The microgravity environment allowed the researcher to use the test cell to mimic the behavior of the atmosphere over a large part of Earth's surface. Results from this experiment were used to improve mathematical models of our atmosphere.

In October 1985, NASA launched a Spacelab mission sponsored by the Federal Republic of Germany, designated Spacelab-D1. American and German scientists conducted experiments to synthesize high quality semiconductor crystals useful in infrared detectors and lasers. These crystals had improved properties and were more uniform in composition than their Earth-grown counterparts. Researchers also successfully measured critical properties of molten alloys.

International Microgravity Laboratory-1, January 1992

More than 220 scientists from the United States and 14 other countries contributed to the experiments flown on the first International Microgravity Laboratory (IML-1) in January 1992. Several biotechnology experiments concerned with protein crystal growth enabled NASA scientists to successfully test and compare two different crystal-growing devices.

A German device called the Cryostat produced superior-quality crystals of proteins from several microorganisms including the satellite tobacco mosaic virus (STMV), which has roles in diseases affecting more than 150 crop plants. As a result of this experiment, scientists now have a much clearer understanding of the overall structure of STMV. This information is useful in efforts to develop strategies for combating viral damage to crops.

IML-1 also carried experiments designed to probe how microgravity affects the internal structure of metal alloys as they solidify. The growth characteristics, determined from one of the experiments, matched the predictions of existing models, providing experimental evidence that current hypotheses about alloy formation are correct.

United States Microgravity Laboratory-1, June 1992 In June 1992 the first United States Microgravity Laboratory (USML-1) flew aboard a 14-day shuttle mission, the longest up to that time. This Spacelab-based mission was an important step in a long-term commitment to build a microgravity program involving government, academic, and industrial researchers. The payload included 31 microgravity experiments using some facilities and instruments from previous flights, including the Protein Crystal Growth facility, a Space Acceleration Measurement System, and the Solid Surface Combustion Experiment. New experiment facilities, all designed to be reusable on future missions, included the Crystal Growth Furnace (CGF), a Glovebox provided by the European Space Agency, the Surface Tension Driven Convection Experiment apparatus (STDCE), and the Drop Physics Module. Investigators used the CGF to grow crystals of four different semiconductor materials at temperatures as high as 1260C. One space-grown CdZnTe crystal developed far fewer imperfections than even the best Earth-grown crystals, results that far exceeded pre-flight expectations. Thin crystals of HgCdTe grown from the vapor phase had mirror-smooth surfaces even at high magnifications. This type of surface was not observed on Earth-grown crystals.

The first Spacelab mission dedicated to United States microgravity science on USML-I. The coast of Florida appears in the background.

Researchers used the STDCE apparatus to explore how internal movements of a liquid are created when there are spatial differences in temperature on the liquid's surface. The results are in close agreement with advanced theories and models that the experiment researchers developed. In the Drop Physics Module, sound waves were used to position and manipulate liquid droplets. Surface tension controlled the shape of the droplets in ways that confirmed theoretical predictions. The dynamics of rotating drops of silicone oil also conformed to theoretical predictions. Experimental and theoretical results of this kind are significant because they illustrate an important part of the scientific method: hypotheses are formed and carefully planned experiments are conducted to test them.

Commander B. Dunbar and L. DeLucas working in the module on USML-1.

Sixteen different investigations run by NASA researchers used the Glovebox, which provided a safe enclosed working area; it also was equipped with photographic equipment to provide a visual record of investigation operations. The Glovebox allowed crew members to perform protein crystallization studies as they would on Earth, including procedures that require hands-on manipulation. Among other results, use of the Glovebox provided the best-ever crystals of malic enzyme that may be useful in developing anti-parasitic drugs. The burning of small candles in the Glovebox provided new insights into how flames can exist in an environment in which there is no air flow. The results were similar (though much longer lived) to what can be seen by conducting similar experiments in freefall here on Earth. (See Candle Flames in Microgravity, in the Activities section of this guide.) The candles burned for about 45 to 60 seconds in the Glovebox experiments. Another Glovebox investigation tested how wire insulation burns under different conditions, including in perfectly still air (no air flow) and in air flowing through the chamber from different directions. This research has yielded extremely important fundamental information and also has practical applications, including methods for further increasing fire safety aboard spacecraft.

Fission sequence of a rotating levitated drop.

The crew of scientist astronauts in the Spacelab played an important role in maximizing the science return from this mission. For instance, they attached a flexible type of glovebox, which provided an extra level of safety, to the Crystal Growth Furnace. The furnace was then opened, previously processed samples were removed and an additional sample was inserted. This enabled another three experiments to be conducted. Two other unprocessed samples were already in the furnace. Spacelab-J, September 1992 The Spacelab-J (SL-J) mission flew in September 1992. SL-J was the first Space Shuttle mission shared by NASA and Japan's National Space Development Agency (NASDA). NASA microgravity experiments focused on protein crystal growth and collecting acceleration data in support of the microgravity experiments.  NASDA's science payload consisted of 22 experiments focused on materials science and the behavior of fluids, and 12 human biology experiments. NASDA also contributed two experiment facilities. One of these, the Large Isothermal Furnace, was used to explore how various aspects of processing affect the structure and properties of materials. The second apparatus was a Free-Flow Electrophoresis Unit used to separate different types of molecules in a fluid.

Zeolite crystals can be grown in the Glovebox Facility. Shown here are photos (at the same scale) of zeolite crystals grown on USML-I (top) and on Earth (bottom). Zeolite crystals can be grown in the Glovebox Facility. Shown here are photos (at the same scale) of zeolite crystals grown on USML-I (top) and on Earth (bottom).

United States Microgravity Payload-1, October 1992 The first United States Microgravity Payload (USMP-1) flew on a 10-day Space Shuttle mission launched on October 22, 1992. The mission was the first in an ongoing effort that employs telescience to conduct experiments on a carrier in the Space Shuttle Cargo Bay. Telescience refers to how microgravity experiments can be conducted by scientists on the ground using remote control. The carrier in the Cargo Bay consisted of two Mission Peculiar Equipment Support Structures. On-board, the two Space Acceleration Measurement Systems measured how crew movements, equipment operation, and thruster firings affected the microgravity environment during the experiments. This information was relayed to scientists on the ground, who then correlated it with incoming experiment data. A high point of USMP-1 was the first flight of MEPHISTO, a multi-mission collaboration between NASA-supported scientists and French researchers.

USMP experiments are mounted on Mission Peculiar Equipment Support Structures in the Shuttle Cargo Bay.

MEPHISTO (designed and built by the French Space Agency, Centre National d'Etudes Spatiales or CNES) is designed to study the solidification process of molten metals and other substances. Three identical samples of one alloy (a combination of tin and bismuth) were solidified, melted, and resolidified more than 40 times, under slightly different conditions each time. As each cycle ended, data were transmitted from the Space Shuttle to Marshall Space Flight Center. There, researchers analyzed the information in combination with data from the Space Acceleration Measurement System and sent back commands for adjustments. In all, the investigators relayed more than 5000 commands directly to their instruments on orbit. Researchers compared experiment data with the predictions of theoretical models and showed that mathematical models can predict important aspects of the experiment behavior. This first MEPHISTO effort proved that telescience projects can be carried out efficiently, with successful results.

The lambda point for liquid helium is the combination of temperature and pressure at which normal liquid helium changes to a superfluid. On Earth, effects of gravity make it virtually impossible to measure properties of substances very close to this point. On USMP-1, the Lambda Point Experiment cooled liquid helium to an extremely low temperature--a little more than 2 K above absolute zero. Investigators measured changes in its properties immediately before it changed from a normal fluid to a superfluid. Performing the test in microgravity yielded temperature measurements accurate to within a fraction of one billionth of a degree- several hundred times more accurate than would have been possible in normal gravity. Overall the new data were five times more accurate than in any previous experiment.

United States Microgravity Payload-2, March 1994 The second United States Microgravity Payload (USMP-2) flew aboard the Space Shuttle Columbia for 14 days from March 4 to March 18, 1994. Building on the success of telescience in USMP-1, the Shuttle Cargo Bay carried four primary experiments which were controlled by approximately 10,000 commands relayed by scientists at Marshall Space Flight Center. USMP-2 also included two Space Acceleration Measurement Systems, which provided scientists on the ground with nearly instant feedback on how various kinds of motion-including crew exercise and vibrations from thruster engines-affected mission experiments. The Orbital Acceleration Research Experiment in the Cargo Bay collected supplemental data on acceleration, providing an indication of the quasi-steady acceleration levels experienced by the experiments.

Science and mission management teams monitor and control experiments from operations centers worldwide.

Throughout the mission, the Critical Fluid Light Scattering Experiment--nicknamed Zeno- analyzed the behavior of the element xenon as it fluctuated between two different states, liquid and gas. First, a chamber containing liquid xenon was heated. Then, laser beams were passed through the chamber as the xenon reached temperatures near this transition point. A series of measurements were taken of how the laser beams were scattered (deflected) as the xenon shifted from one state to another. Researchers expected that performing the experiment on orbit would provide more detailed information about how a substance changes phase than could be obtained on Earth. In fact, the results produced observations more than 100 times more precise than the best measurement on the ground.

The Isothermal Dendritic Growth Experiment (IDGE) examined the solidification of a material that is a well-established model for metals. This material is especially useful as a model because it is transparent, so a camera can actually record what happens inside a sample as it freezes. In 59 experiments conducted during 9 days, over 100 television images of growing dendrites were sent to the ground and examined by the research team. Dendritic growth velocities and tip radii of curvature were measured. Results obtained under certain experiment conditions were not consistent with current theory. This inconsistency was the subject of subsequent research on USMP-3. In another successful demonstration of telescience, the team relayed more than 200 commands to the IDGE, fine-tuning its operations. USMP-2 also included a MEPHISTO experiment. On this mission, the MEPHISTO apparatus was used for U.S. experiments to test how gravity affects the formation of crystals from an alloy of bismuth and tin that behaves much like a semiconductor during crystal growth. Metallurgical analysis of the samples has shown that interactions between the molten and solid alloy during crystallization play a key role in controlling the final morphological stability of the alloy. Another USMP-2 materials science experiment used the Advanced Automated Directional Solidification Furnace (AADSF). An eleven day experiment using the AADSF yielded a large, well-controlled sample of the alloy semiconductor, HgCdTe. The results of various analysis techniques performed on the crystal indicate that variations in the acceleration environment had a marked effect (due to changing residual fluid flow) on the final distribution of the alloy's components in the crystal.

A dendrite grown in the Isothermal Dendritic Growth Experiment aboard the USMP-2. This is an example of how most metals solidify.

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