Marshall scientists continued probing the formation of novel materials, including the lowest-density material ever made by mankind, and the behavior of the ground on which we stand. Marshall also was designated by NASA as the lead center for microgravity research.
The most exciting news came from one of the most fragile and lightweight specimens ever produced by SSL. An SSL experiment aboard a Starfire rocket flown for the University of Alabama in Huntsville yielded the first space-produced aerogel, a foam-like product that has only three times the density of air - one writer called it "frozen smoke" - yet can protect the human hand from the heat radiated by a blowtorch.
Aerogels have been produced in ground-based laboratories, but have low quality because gravitational forces cause sedimentation leading to a dense foam near the bottom of the container and a thin foam near the top. An apparatus aboard the Starfire rocket produced a small specimen of aerogel with uniform cell size, wall thickness, and density. Potential applications for aerogels include highly efficient transparent insulation in window panes, skylights, and other commercial uses. Producing aerogels in space helps us understand better how to make aerogels on the ground.
Anyone who has watched sand castles collapse at the beach will be familiar with the Mechanics of Granular Materials (MGM) experiment flown in 1996. MGM applies the microgravity environment of space to the behavior of soil under very low effective stresses. Ground-based experiments have long established the behavior of soil under high effective stresses, that is, high compression and sideways strains.
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Sample holder for the Mechanics of Granular Materials experiment is shown before being packaged in a water jacket for flight. |
The values for low effective stresses are needed so we can understand better the mechanics of soil during earthquakes, the erosion of riverbanks and ocean floors, the movement of powdered pharmaceuticals while being manufactured, and many other phenomena. The results can have implications in civil engineering, conservation, industrial processes using powders, and even the exploration of the planets.
A continuing challenge in protein crystal growth studies is the proper illumination of crystals by X-rays to make crystallograms from which the structure of proteins may be deduced. X-ray sources are like ordinary light bulbs: they radiate in all directions and a pinhole aperture must be provided to restrict the illumination to the subject.
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Dots and shadows (left) reveal the internal structure of crystals as shown in this X-ray crystallogram of lysozyme. Capillary X-ray optics, developed by SSL and the State University of New York-Albany, will provide better illumination for more complex proteins like those grown in the Diffusion-Controlled Apparatus for Microgravity (right) was developed by SSL to grow protein crystals at slow, controlled rates in space. The patented design - a little larger than a 35 mm film can - has produced promising crystals in a long stay aboard the Mir space station. |  |
Working with the State University of New York at Albany and X-ray Optical Systems Inc., also of Albany, SSL investigators developed capillary optics which capture X-rays and turn them into parallel rays. This allows crystallograms to be collected faster, or to be made with low-power sources on Earth or possibly aboard International Space Station.
Intense magnetic fields, up to 100,000 times that of the Earth, were used to counteract the effects of gravity in growing crystals such as mercury-cadmium-telluride. Many of the defects that form in crystals are caused by convection (hot fluids rise, cold fluids sink). Intense magnetic fields reduce these flows by effectively freezing the convective motion while the material is still molten. These experiments were extremely helpful in interpreting results from SSL experiments with the Advanced Automated Directional Solidification Furnace (AADSF) on the second U.S. Microgravity Payload mission (USMP-2). These data demonstrated for the first time the importance of residual flows when processing electronic materials in space.
1996 saw SSL direct the third flight of the U.S. Microgravity Payload (USMP-3) in April, and start preparations for the USMP-4 mission in late 1997. SSL also was preparing for NASA's next Spacelab mission, Microgravity Science Laboratory 1 (MSL-1). SSL scientists have played leading roles in Spacelab missions since Spacelab 1 in 1983. MSL-1 will carry investigations from Marshall, other NASA centers, and academic and international institutions. Both MSL-1, involving a four-person science crew, and the teleoperated USMP-4 will set the stage for SSL experiments aboard the International Space Station.
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The Advanced Automated Directional Solidification Furnace (about 3 feet tall) was flown on USMP-3 during 1996. Its fourth flight will be on USMP-4 in 1997. |
Last updated March 5, 1997