July 30, 1998 ITHACA, N.Y. -- Most students work in a library, laboratory or classroom, but Cornell University undergraduate Greg Aloe floats in space aboard the same NASA aircraft that Tom Hanks used to simulate zero gravity while filming Apollo 13.
Aloe has nose-dived in the stripped and padded Boeing 707 more than 175 times, free falling "like a rock" a dizzying 1.25 miles in 25 seconds. What participants have dubbed the "vomit comet" climbs and then plummets 40 or 50 times during each two-hour flight.
In the weightlessness that occurs during the free fall, Aloe conducts experiments that could shed light on what makes manufactured solid granular materials separate into their component parts, both with and without gravitational force. The work, now in its feasibility stage, could aid engineers on future lunar and Martian missions seeking to extract fuel, water or other materials from soil in conditions of low gravitational force. A Cornell senior from Madison, Conn., majoring in mechanical engineering, Aloe serves as a part-time research assistant on the project headed by Michel Louge, Cornell professor of mechanical and aerospace engineering, and James T. Jenkins, Cornell professor of theoretical and applied mechanics.
Aloe is one of seven Cornell undergraduate engineering students working on the NASA-funded project with their professors. But he is the only one of the seven to be medically cleared by the space agency to fly on the KC-135. This involved compression chamber tests mimicking low-oxygen, high-altitude conditions to see if he could withstand the extreme conditions of free fall.
With 20 seconds of weightlessness, called microgravity, during each nose dive, Aloe has had a total of almost an hour of free fall during his four flights to carry out experiments. Aloe prides himself on never getting sick on the plane, even though about half of the researchers who fly on the KC-135 have gotten sick. It's common, he says, to see full vomit bags floating to the rear of the plane.
"I think the weightlessness feels a lot like the bouncing buoyancy in scuba diving but without the water to displace if you try to swim. Although a very intense roller coaster may be the closest thing to it you can experience on earth, the feeling in the KC-135 is much weirder. Nothing really can prepare you for it," he says.
Aloe describes the experiments during the free fall as "understanding how solids of two sizes or two densities collide and separate when agitated." From this, he says, researchers hope to learn how to improve the mixing of granular or liquid materials and to prevent them from separating, both on Earth and in space. Microgravity slows down the mixing process, isolates a mechanism independent of gravity and makes it much easier to observe the trajectories of particles colliding, before and after impact, with a fast digital video camera. "This allows us to capture and download velocity and other measurements," says Aloe.
Jenkins, Louge and research assistant Birgir Arnarson originally developed theories and computer simulations to analyze how particles of different sizes might behave in systems of colliding particles. Cornell research engineer Stephen Keast then designed and built a prototype device called a shear cell to test the theories and simulations. Resembling a 3-foot-long racetrack, the shear cell consists of a motor that propels a chain along the inside boundary. Small acrylic or ceramic spheres of various sizes are released into the track.
"As the beads bump the moving chain, they pick up energy and then collide with each other and the boundaries," explains Louge, who has flown the KC-135 eight times, including three with Aloe. The two expect to make further flights to measure chrome and steel beads' agitation and impact properties, such as velocity and fluctuation. With the help of Cornell Theory Center's supercomputer, the researchers hope to predict how the solid particles will separate by their properties.
Other Cornell collaborators who work on the flow and computer visualization aspects of the project include Anthony Reeves, professor of electrical engineering, Elaina McCartney, a computer scientist in mechanical and aerospace engineering, and Michael Garon, a graduate student in electrical engineering.
The other undergraduate students who worked on the impact experiment include Rowin Andruscavage, a junior in mechanical and aerospace engineering, and Claudio Bazzichelli, who just graduated from the same department; Amelia Dudley, sophomore in engineering; and Patrick Florit, Josh Freeh, Lance Hazer and Rami Sabanegh, all seniors in mechanical and aerospace engineering.
EDITORS: For a color computer simulation of the "racetrack," showing a shear cell with grains of identical density but different sizes, see http://www.mae.cornell.edu/research/microgravity/granular-simulations.html. For a photograph of the prototype shear cell, see http://www.mae.cornell.edu/research/microgravity/cell.html.
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