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Sept. 15, 1999: You've climbed to the top of the pack, you're a PhD in astrophysics or a Top Gun pilot, you've just been selected to be an astronaut. So what's your first task? Go back to school to become a generalist after studying to be a specialist. Right: Dr. Sharon Cobb of NASA's Marshall Space Flight Center examines a model of a crystal lattice. One of the key points of her lecture is that processing materials in the microgravity of space reduces defects like the spot, at the center of the model, where an extra row of atoms has wedged into the lattice. Links to 600x425-pixel, 96KB JPG. Or click here for 3024x2252-pixel, 1.2MB JPG. Credit: NASA/Marshall Because astronauts are called upon to do a little of everything on the job, their training encompasses far more than how to operate the Space Shuttle or - with the new candidates in training - the International Space Station (ISS). Among the many fields astronauts must know is materials science in microgravity, one of the principal missions for ISS. Materials science research aboard the ISS is sponsored by the Microgravity Research Program at NASA's Marshall Space Flight Center in Huntsville, Ala. Approximately 60 percent of the planned science experiment time aboard ISS is devoted to the microgravity sciences and commercial microgravity investigations. "This type of training is challenging because the astronauts have a range of backgrounds from mathematics to materials science," said Dr. Sharon Cobb, the project scientist for the Materials Sciences Research Facility here at NASA/Marshall. Cobb recently gave an introductory class, including hands-on labs, to the most recently selected astronaut candidate class at Johnson Space Center. "I gave an overview - with a number of essential details - of what materials science is and why we want to do this research in microgravity. Later the astronauts will get more detailed training on specific experiments as the hardware is developed for flight." |
From this came the realization that no one fully understood what would happen if gravity's effects were removed from materials that were liquefied, mixed, and resolidified. Early flight experiments were conducted aboard the last Apollo missions. The discipline grew and became a major aspect of Skylab's experiments in 1973-74, and a centerpiece of Space Shuttle and Spacelab missions during 1983-98.
Cobb reminded the astronaut candidates that advances in materials science in 1-g make their missions possible, from the new lithium-aluminum alloy that lightens the Shuttle External Tank so more payload mass can be carried to orbit, to the urethane-coated nylon pressure bladder that will keep them in a safe atmosphere during space walks. "Manufacturing is 17 percent - $1.2 trillion - of the U.S. gross domestic product," Cobb explained. "That means that even modest improvements in materials and their production can have great economic impact. |
For example, the 1998 Metalcasting Industry Technology Roadmap lists "lack of knowledge of process-microstructure-chemistry-property interactions [as one of the ] major technology barriers in materials." "To make substantial advances," Cobb continued, "materials processing must transition from a historically trial-and-error art to become a predictable, controllable technology in the future." The epitome of the older method is the story of Thomas Edison perfecting (not inventing) the light bulb by trying everything as a long-life filament, and then testing virtually every type of bamboo after he happened upon that. The properties of materials, especially under various conditions, were just becoming known to scientists then. |
Scientists have reached the point where a material's interactions with its container may alter sophisticated measurements of a property, or mask a fundamental phenomenon. For example, unavoidable convection - where warm, light fluids rise and cold, dense fluids sink - disturbs the formation of an alloy or electronics crystal and causes defects. Gravity is an inescapable factor in the equations because it's always there - unless you go to orbit. Unless you go into orbit. You're still a captive of Earth's gravity - that's what holds you and the Moon in orbit - but you're falling continually so the effect is indistinguishable from gravity being turned off. Tiny residual accelerations remain, so scientists refer to microgravity, not zero-G. The net result is that a new range of possibilities now opens for materials science. "The goal of materials processing in space is to develop a better understanding of the relationship between processing, structure, and properties so that we can reliably predict the conditions required on Earth to achieve desired materials properties," Cobb said. |
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This does not mean factories in space, but labs in space to improve factories on Earth. The discovery that something subtle is happening inside a material when it forms may allow scientists and engineers to figure out how to manipulate a phenomenon to make better materials. Left: Artist's concept of astronauts at work inside the U.S. Lab Module of the International Space Station. Links to 1169x1421-pixel, 88K GIF. Credit: NASA. Those discoveries will come from principal investigators working in labs on Earth, but using samples that astronauts have processed in space. Cobb's purpose was to help the candidates understand the subtle and precise nature of the experiments they soon will be asked to perform. For example, astronauts need to know the range of phases that materials have under different conditions. While we are most familiar with just three - solid, liquid, and gas, like ice, water, and steam - scientists often deal with in-between or even multiple states. Cobb likens it to mixing chocolate and vanilla. What you get depends on how much you mix and on the temperature. A diagram of the different phases shows how you may get hot chocolate, vanilla extract, chocolate malt, or even chocolate ripple. Right: A materials phase diagram for chocolate and vanilla is an appetizing way of illustrating how different compositions and temperatures can change the final product. The eutectic line indicates the temperature where the liquid transforms into two types of solids, like chocolate ripple. The solvus line indicates the limit for how much vanilla can be dissolved into the chocolate as a function of temperature. Links to 1151x709-pixel, 41K GIF. Credit: Ken Jackson, University of Arizona. "In the same manner, metal alloys or semiconductors can yield completely different products if the processing conditions vary just a little," she continued. "We will really be relying on the astronauts to successfully conduct the on-orbit procedures for these experiments." |
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The experiments will be conducted in several racks, each 1 meter wide (almost 40 inches) that will be installed aboard ISS over the next few years. Cobb is the science community's point of contact for the Materials Sciences Research Facility which comprises three Materials Science Research Racks. (ISS will also host facilities for research in fluids, combustion, biotechnology, and other areas.) The MSSR-1 will carry a total of five experiment furnaces from NASA and the European Space Agency. Candidates for MSSR-2 and -3 include furnaces that would take half the rack. "I often get asked why we need so many different furnaces," Cobb said. "Well, most of us have several ovens at home - a toaster oven, a microwave oven, a regular convection oven, and then four hot eyes on the top of the oven." In the same manner, it's almost impossible to design one furnace that would satisfy every experiment, so several furnaces are designed with special capabilities. Some are isothermal, meaning that the whole sample is heated and cooled evenly. Some use gradient heating where the hot zone travels down the length of a sample, followed by a cool-down zone. Others provide for rapid quench, like dipping a hot horseshoe in a bucket of water, to freeze in the history of the liquid for subsequent examination on the ground.
Cobb gave the astronaut candidates a little practice in these areas with some basic experiments that parallel what is done in classrooms and in space. In one demonstration, the candidates grew crystals of succinonitrile, a chemical that forms dendrites, tree-like crystals, similar to what happens inside metals. Already, similar experiments aboard the Space Shuttle have caused scientists to rewrite some basic assumptions about what happens in that magical instant as a metal turns from liquid to solid. More advances are expected as the ISS is completed and becomes an orbiting materials laboratory. |
More Space Science Headlines - NASA research on the web Life and Microgravity Sciences and Applications information from NASA HQ on science in space Microgravity Research Programs Office headquartered at Marshall Space Flight Center Microgravity News online version of NASA's latest in Microgravity advancements, published quarterly. |
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