Some Accomplishments in 25 Years of Microgravity Science Nearly 30 years have passed since the first microgravity experiments were performed on the Apollo spacecraft during their return voyages from the moon, and it has been nearly 25 years since Skylab, the first spacecraft to carry user-class facilities dedicated to processing materials in space. The space-shuttle has served numerous times as a platform for microgravity research, and MSL-1/STS-94 marks our arrival at the threshold of the coming decade of microgravity science on the space station. At this point in time, it is instructive to sample some of the things we have learned from our microgravity research in space and on the ground. Of course it is impossible to cover every aspect of microgravity science in the span of one web-page, but we hope you'll get an idea of the some of the great science that can be done in space! Protein Crystal Growth Combustion Research Materials Science and Research Fundamental Physics Research
		Protein Crystal Growth One of the most exciting results obtained thus far from the microgravity program has been the success of protein crystal growth experiments that have flown on a number of shuttle missions, the Mir space station, and on several foreign unmanned recoverable capsules. This activity was stimulated by the successful experiments of Littke and Johns (Science 225, 203, 1984) on the first Spacelab mission. Most of the crystal growth experiments that flew on the shuttle prior to Challenger were designed to test concepts for growing crystals in space. Since that time, we have developed the ability to grow high-quality crystals in space. On the first flight after Challenger (STS-26), for example, several exciting results were obtained (DeLucas, et al., Science, 246, 651, 1989). The important human proteins gamma interferon, isocitrate lyase, and porcine elastase crystals grown on STS-26 were generally larger, and provided X-ray diffraction quality better than the best crystals of these proteins ever grown on Earth. Other shuttle missions since STS-26 have also produced outstanding crystal growth results.
		NASA researchers grew protein crystals on STS-42/IML-1 using two different techniques. Dr. Alexander McPherson of the University of California at Riverside shared a protein crystallization device developed by the European Space Agency with two German scientists. This apparatus, called the Cryostat, combines dissolved protein solutions with dissolved substances that stimulate crystallization. A second group of scientists, led by Dr. Charles Bugg of the University of Alabama at Birmingham, used a NASA-developed device called the Vapor Diffusion Apparatus which initiates crystal formation once the protein solutions become increasingly concentrated through water evaporation.
Tobacco Mosaic Virus Crystal Grown on IML-1		Dr. McPherson's results obtained for the Satellite Tobacco Mosaic Virus (STMV) crystals--one of the smallest viruses known--were extremely successful. STMV crystals were obtained from the Cryostat that were 15 times the volume of any seen in the laboratory. Dr. McPherson reported that these crystals gave the "best resolution data obtained on any virus crystal, by any method, anywhere." Analysis of these crystals allowed Dr. McPherson to visualize the nucleic acid contained in STMV for the first time. Another successful protein crystallized for Dr. McPherson was canavalin, a protein obtained from bean plants and a major nutrient world-wide. Although not large, the unusual "shot glass" shape of the crystals may help scientists learn how gravity affects protein crystal growth. Another very notable protein for which excellent results were obtained is human serum albumin (HSA), the most abundant protein in the circulatory system. One HSA crystal grown on IML-1 yielded better structural data than any grown on the ground. This information has been used by researchers at the NASA Marshall Space Flight Center to further refine the molecular structure of HSA, and improve our knowledge of how HSA transports chemicals such as aspirin in the bloodstream. From over 33 proteins, ranging from insulin to HIV reverse transcriptase, the microgravity environment for crystal growth improves over the best-case Earth-grown crystals in the following ways: Larger Crystals in 45.4% of the cases New Crystal Structures in 18% of the cases At least a 10% increase in the X-Ray Crystallography Brightness in 58% of the cases. Less thermal motion in 27.2% of the cases An X-Ray Crystallography resolution improvement of ~0.3 Angstroms in 42.4% of the cases An X-Ray Crystallography resolution improvement of 0.3 to 0.5 Angstroms in 9.9% of the cases An X-Ray Crystallography resolution improvement of 0.5 to 1.0 Angstroms in 9.9% of the cases Thus in almost half of our handful of space-flight experiments, we can produce better crystals than have ever been produced on Earth, in thousands of experiments, by the world's most qualified researchers whose professional success depends heavily on obtaining the molecular structure from X-ray diffraction of these crystals.
		Despite these successes, there are many questions about Protein Crystal Growth in space that we do not understand. Why should protein crystals grow better in low-gravity? Why do some systems show a marked improvement in low-gravity, while others do not? Are the growth conditions that are determined on Earth optimum for growth in microgravity? How does the residual acceleration environment on the spacecraft affect the growth of crystals? Are the crystals degraded in the process of returning them to Earth for analysis? Can the lessons learned in space be applied to grow better crystals on Earth? The ability to design a drug based on the knowledge of the structure of a protein is an emerging technology, and one that is still in its infancy. However, the promise of this technology is enormous, and the United States is clearly the leader. The limiting step in this technology is still the ability to grow diffraction quality crystals of the materials of interest. Even just a few fractions of an Angstrom (one ten-billionth of a meter) improvement in resolution can be a decisive factor in mapping out the active site in a target protein. Data from space-grown crystals has been used to refine the structures of a number of proteins, and in some cases to obtain the structure of a protein for the very first time.
		Combustion Research MSL-1/STS-83 contained the first set of large-scale combustion experiments for operation in microgravity. However, it did not mark the first time that NASA had performed combustion experiments aboard the shuttle. On USML-1, scientists investigated the sustained behavior of a candle flame in microgravity. In a quiescent, microgravity environment, the dominant mode by which mass and heat are transferred in and around a flame is by diffusion. Before this experiment was performed, it was unknown whether the rate of diffusion for both fuel and oxygen was fast enough to sustain low-gravity candle flames in air. After lighting a candle in microgravity and allowing the flame to stabilize, the microgravity candle flame in air becomes and remains hemispherical and blue. It is also apparently soot-free. When a flame does go out, the fact that the flame tip is the last point of the flame to survive suggests that it is the location of maximum fuel reactivity. This is unlike normal gravity, where the location of maximum fuel reactivity is the flame base.
		Even though the first flight of MSL-1 was shortened, much was learned about combustion on this flight as well. For example, from the Laminar Soot Process Experiment (LSP), two significant findings were made. First, we learned that the onset of soot emission coincides with the extinction of combustion at the downstream (tip) end of the flame. In other words, when burning stops at the tip of the flame, soot production starts. This helps explain why practical flames on Earth demonstrate a strong correlation between the onset and subsequent degree of soot and hydrocarbon emissions. Second, we learned that the microgravity flames exhibit "laminar smoke points", or a maximum fuel flow rate where the flame just begins to emit soot, analogous to the flames we are familiar with on the ground. This finding resolves a controversy over whether undisturbed microgravity flames would exhibit these laminar smoke points.
MSL-1/STS-83 image of flame balls obtained in 4.9% H2/ 13.8% O2 / 85.3% CO2 mixture. This is one of two runs performed on the flight, and the field of view is 22.5 cm x 30 cm.		The SOFBALL experiment on MSL-1/STS-83 also gained new insight into the physics of the combustion process. Two of the fifteen scheduled test burns on the experiment were conducted on the mission. All of the scientific instrumentation performed extremely well. Two different types of mixtures were burned, and both burned much longer than expected based on current theoretical understanding. Two new insights have already been obtained, namely on the speed at which the flames drift and the characteristics of their thermal radiation. These tests have provided an exciting, though preliminary, understanding of the interactions of the two most important phenomena in combustion materials: Chemical Reaction and Chemical Transport Processes in the unequivocally simplest possible configuration. The data obtained are crucial for comparison with models of flame stability and propagation limits, which are needed for fire safety assessment and the design of efficient, clean-burning combustion engines. With 16 days planned for the next flight of MSL-1 on STS-94, the Structure of Flame-Balls at Low Lewis-Number (SOFBALL), Fiber Supported Droplet Combustion Experiment (FSDC), the Droplet Combustion Experiment (DCE), as well as the Laminar Soot Process Experiment (LSP) experiments all promise to add significant new knowledge to our understanding of the fundamental processes of combustion. More!!! Combustion Research at NASA Lewis
		Materials Science and Processing
Mercuric Iodide crystal growing aboard the STS-51B/Spacelab 3 Mission. The crystal is the small red object near the center of the photograph.		Electronic and Photonic Materials In two IML-1 experiments, scientists grew crystals of the inorganic compound mercuric iodide. These crystals have exceptional properties which allow them to act as sensitive, room-temperature X-ray and gamma ray detectors. On Earth, these crystals frequently have defects that limit their usefulness. Both IML-1 experiments involved heating a mass of mercury iodide source material so that it slowly evaporated. As the mercury iodide vapor cooled, it deposited on a small "seed" crystal of the same material, causing it to increase in size, or "grow". The first experiment was performed by Dr. Lodewijk van den Berg of EG&G Corporation in the NASA-developed Vapor Crystal Growth System (VCGS). This experiment--a follow-on to successful research in the VCGS during the Spacelab-3 mission (1985)--produced a large mercuric iodide crystal. Analysis of this crystal shows that it has a more uniform molecular structure than crystals grown on Earth. Electronic measurements indicated that the IML-1 crystal is more efficient, improving its characteristics as an X-ray and gamma ray detector. These results helped to confirm the Spacelab-3 results which also indicated space-grown crystals to be more efficient. Dr. Lodewijk van den Berg concluded from these results that vapor crystal growth is a process that can be transplanted successfully to space, where higher quality crystals with improved electronic properties can be grown. In a separate and complementary mercuric iodide experiment sponsored by the French Space Agency, six crystals were grown under conditions where pressure, temperature, and seed crystal orientation varied. The chemical analysis showed an improved purity for the space-grown portion of the crystals.
Pilot Rick Hauck aboard STS-7 with the Monodisperse Latex Reactor (the white circular object behind his head)		Monodisperse Nanomaterials The first space product sold commercially from the microgravity program in June 1984 was monodisperse latex spheres. These were used and sold as calibration standards by the National Bureau of Standards. In order to calibrate equipment such as electron microscopes, laser light scattering instruments, and particle counters, one requires extremely small particles of known size, whose variations in size are at an absolute minimum. The Monodisperse Latex Reactor flew on a total of eight shuttle flights. It generated tiny uniform space-produced latex spheres whose sizes varied less than 0.4 percent for spheres only 10 microns (10 one-millionths of an inch) across.
		Containerless Processing of Materials Containerless processing of materials in microgravity allows scientists to melt a small sample of material, for example a metal, and then study, analyze, probe, and eventually solidify the material without any physical contact between the material and a container wall. Elimination of the container allows for samples to be deeply under-cooled before any solidification occurs. The TEMPUS facility, which has flown twice ( IML-2/STS-65 and MSL-1/STS-83), and will fly again on MSL-1/STS-94, is designed to study various metals and alloys in the under-cooled state, and to allow scientists to perform measurements of properties such as surface tension and viscosity. When under-cooled metals are eventually solidified, the solidification (or "freezing") of the metal happens extremely fast, sometimes in as short a time-span as a few hundred millionths of a second! This allows for scientists to obtain highly refined grain structures in these metals, or to trap the metals in amorphous or quasi-stable states that cannot otherwise be obtained. On MSL-1/STS-83, the TEMPUS hardware performed extremely well, and was able to obtain record levels of under-cooling for several samples. In some cases, these liquid metals can remain liquid at temperatures 300 degrees below their normal solidification/freezing point. With an anticipated 16-day mission on MSL-1/STS-94, TEMPUS promises to provide enhanced levels of scientific understanding of these new and interesting forms of metals and alloys.
Drawing of a zeolite crystal like those investigated on USML-1.		Zeolites* Zeolites are a class of crystalline aluminosilicate materials that form the backbone of the chemical process industry worldwide. They are used primarily as adsorbents and catalysts and support to a significant extent the positive balance of trade realized by the chemical industry in the United States, around $19 billion in 1991. The magnitude of their effects can be appreciated when one realizes that since their introduction as "cracking catalysts" in the early 1960's, they have saved the equivalent to 60 percent of the total oil production from Alaska's North Slope. Thus the performance of zeolite catalysts can have a profound effect on the US economy. It is estimated that a 1 percent increase in yield of the gasoline fraction per barrel of oil would represent a savings of 22 million barrels of crude oil per year, representing a reduction of $400 million in the United States' balance of payments. Flight results, for example from USML-1, on zeolite growth in microgravity have revealed that larger and more defect free crystals of zeolite can be grown in high-yield in space. The size increase for the chemical formulations flown varied between 10 and 50 percent. The result of these experiments produced the first perfect zeolite crystal with the theoretical limit of a ratio between silica and aluminum (Si/Al) near one. These activities, as well as any others, which result in improvement in zeolite catalyst performance are of significant scientific and industrial interest. *From Sacco, et al. 1993 and references therein.
ZBLAN manufactured on the ground tends to crystallize, severely degrading its optical properties. However ZBLAN manufactured in low-gravity appears to retain its glass-like state.		Glasses and Ceramics Discovered by a team of French researchers in 1974, ZBLAN is named after the heavy metals found in the chemical composition of the material: zirconium, barium, lanthanum, aluminum, and sodium (chemical symbol "Na"). ZBLAN is a member of the heavy metal fluoride family of glasses, and has promising applications in fiber optics. It is highly transparent in the infrared region of the electromagnetic spectrum, thus opening an entirely new energy range for optical fiber communications, sensing, and technology development. This research is one example of our ongoing search for knowledge and scientific understanding in the microgravity program. ZBLAN research has been flown on suborbital rockets and aboard NASA's KC-135 Research Aircraft. Soon we hope to fly it on the space shuttle and space station, because to develop this new material fully will require some more hard science be done. In theory, one should be able to make a ZBLAN optical fiber cable that has the capability to carry more than 100 times the amount of data carried by today's traditional silica-based optical fiber cables. In practice, however, the best that has been achieved has only been about 1/5 of current cables. This is primarily because of the fact that when you make ZBLAN on the ground, it has a tendency to crystallize - to come out of its glass-like state - which severely degrades its optical properties. The two pictures at the left demonstrate this. The ZBLAN at the top, made on Earth in a one-gravity environment, shows a great deal of non-uniformity and inhomogeneities due to its crystalline state. By contrast, the ZBLAN on the bottom was made aboard a Conquest-1 suborbital rocket flight. Its glassy nature is readily visible, as are some bubbles that formed when the sample inadvertently came in contact with the container. Many researchers perform experiments in space in order to make very high-quality crystals, but in low gravity ZBLAN doesn't crystallize. Potential areas of application for this material include medical surgery and cauterization, temperature monitoring, infrared imaging, fiber-optic lasers, optical power transmission, and a host of other areas. A recent marketing survey indicated that the annual impact of ZBLAN on the economy might total as much as nearly $8 billion.
Aerogel is the lowest-density solid known, with tremendous insulating properties. NASA research in space is trying to help us understand how to make it clear. Aerogel can protect a piece of chocolate from the heat of a blowtorch.		Aerogel Research Aerogel is the lightest solid material known - only three times the density of air - and has tremendous insulating capability. A block the size of a human weighs less than a pound, but is able to support the weight of a subcompact car or about half a ton. A one-inch thick Aerogel window has the same insulation value as 15 panes of glass and trapped air - which means a conventional window would have to be ten inches thick to equal a one-inch thick Aerogel window. However, when made on the ground, it has a hazy or smoky appearance. NASA scientists are experimenting with Aerogel in space and believe that they may be able to learn how to make the foam-like material transparent. Results from recent space research indicates that we're on the right track. The hazy nature of the Aerogel is caused by non-uniform pore-sizes in the material. While most of the pores are much too small to interact with and scatter light, a few percent of the pores are much larger, on the order of the wavelength of blue light. These pores act as scattering points for the light, reducing the material's transparency. Scientists believe that the non-uniformity in the pore size is generated while the Aerogel is being formed, by gravity-induced flows in the gel mixture. To test the theory, 16 samples of Aerogel were formed aboard an 8-minute microgravity flight of a Starfire sub-orbital rocket in April 1996. This space-made aerogel demonstrated a 4-fold reduction in the pore-size, and a calculated scattering-reduction factor of 4,000. Aerogel has been used in the space program as the insulating material aboard the Mars Rover scheduled to land on July 4, 1997, and aboard the upcoming Stardust mission to retrieve material from a comet and return it to Earth. Scientists are preparing for a 1998 flight of Aerogel aboard the space shuttle, where we'll be able to test Aerogel with longer exposure to low-gravity.
		Fundamental Physics Research
		Lambda Point for Liquid Helium The lambda point experiment flown in October 1992 aboard USMP-1 involved the best measurement of the heat capacity of liquid helium as it changes phase from the superfluid to the normal fluid phase, at temperatures within only one-billionth of a degree-K of the transition temperature. The purpose of the experiment was to test rigorously the range of validity of a Nobel Prize-winning theory as it pertains to critical phase transitions. On the ground, hydrostatic pressure effects caused by gravity result in degradation of the data as the temperature of liquid helium approaches the critical point. During the space flight experiment, in the absence of these gravity-induced pressure effects, a greater than ten-fold increase in resolution was achieved. Overall, the analysis of the results from this experiment show that in space, the measurable lambda point may be 10,000 times better-defined than the best current Earth-based measurement. last updated June 18, 1997 Authors: Dr. John Horack Curator: Linda Porter NASA Official: Dr. Greg Wilson