Deborah A. Levin, Ph.D.
Professor of Aerospace Engineering
233E Hammond Building
Penn State University
University Park, PA 16802
Phone: 814-865-6435 / Fax: 814-865-7092
E-mail: dalevin@psu.edu
In 2003, the Space Shuttle Columbia broke apart as it re-entered the atmosphere at hypersonic speeds over the southwestern United States. The cause was a 6- to 10-inch hole in the left wing. As the shuttle was taking off days before, a piece of foam insulation broke off the external propellant tank and hit the wing’s leading edge, puncturing the thermal protection tiles. When the vehicle descended, speed, heat, and atmosphere acted so forcefully on that hole that the wing and eventually the shuttle itself disintegrated.
As the loss of Columbia and her crew illustrates, understanding how gases and materials interact at hypersonic speeds is crucially important to the safe return of vehicles from space. Because the problem comprises issues in physics, chemistry, and aerodynamics, looking into it requires cross-disciplinary expertise. With a doctorate in chemistry, Professor Deborah Levin of the Penn State department of aerospace engineering was distinctively qualified to tackle the challenge.
“Previously, industry had been using simple correlation models of holes of various sizes to assess at the time of an accident whether vehicle occupants would be safe on their return flights,” Levin explained. “But to make progress in understanding the problem, it was necessary to invest time and energy to come up with a fundamental approach. Researchers at NASA Langley and Johnson recognized that the problem would be extremely difficult. So they said, essentially, ‘Why don’t you have a go at it?’”
Levin recognized that the Navier-Stokes equations, the traditional fluid dynamics approach, might not applicable to the problem. In fact, using them to try to solve for thermal protection holes could lead to misleading results. That’s because holes such as the one incurred by Columbia are so small that to model the conditions requires the modeling of collisions between gas atoms. So, instead of a fluid dynamics approach, Levin used gas kinetic approach, best modeled by the direct simulation Monte Carlo method.
She was on the right track, but when she presented her early research to government and industry representatives, they suggested there were so many possible variables in the Shuttle re-entry that modeling would never lead to a meaningful solution. So Levin abandoned the such simulations for a while and turned to consider recent arcjet experiments. She measured the shape change and material loss of thermal protection tiles selectively cracked and placed in arc jet test chambers to simulate the experience of re-entry into the atmosphere. In doing this, she saw something very interesting. Heat transfer and multiple chemical reactions took place during the experiments, but a single reaction predominated: the effect of atomic oxygen on the tile’s bare carbon fibers. “We could have kept busy modeling 100 chemical different reactions,” she said. “But if we had done so, we would have missed the forest for the trees.”
Based on the data collected, Levin devised new computer models and then performed simulations of four more sets of experiments to see if they bore out her predictions. They did. In fact, in one case, Levin’s team took a very complicated 3-dimensional symmetry, a wing shape, and watched it being transformed by the arc jet exactly as predicted into a shape more like a bicycle seat. “I felt as if we had pulled a rabbit out of a hat,” Levin said.
Potentially, Levin’s research will form the basis of best-practices techniques for NASA and industry to implement in the event of damage to a vehicle’s thermal protection systems. “The bottom line,” Levin said, “is that manned re-entry will be safer.”
Levin’s understanding of gas dynamic flows also forms the foundation of another area of her research. With support from the Air Force Office of Scientific Research, she has studied condensation in supersonic expansions in order to learn more about the properties of plumes formed by chemical propellants. This research eventually could, for example, enable observers to glean important information about a foreign country’s weapons program’s sophistication just from observing the plume trailing behind a test missile. In 2006, Levin earned the Penn State Engineering Society’s outstanding research award for her work on this subject.
Deborah Levin grew up on Long Island, the daughter of a stockbroker and an elementary school teacher. In high school, she loved chemistry but remembers her best friend’s mother discouraging her pursuit of it.
“She told me the boys sit in class and don’t say anything, but they understand it,” Levin recalls. “The implication was that being a girl, I didn’t – or not at the same level.” Levin, who today is the only woman member of Penn State’s aerospace faculty, went on to defy everyone’s expectations but her own, earning first a bachelor’s degree in chemistry at SUNY Stonybrook and later her Ph.D. in chemistry at Caltech in 1979.
It was also at Caltech that she met her husband, Arne Fliflet, On graduation, they moved to the Washington, D.C., area where he went to work for the Naval Research Lab, and she took a job with the Institute for Defense Analyses (IDA). She was doing operational testing and evaluation for the military in the mid 1980s when the Reagan strategic defense initiative offered her the opportunity to study hypersonics, how gases interact with bodies moving through them at speeds much faster than sound. Levin wanted to re-connect with the computational research she had done as a graduate student so -- along with a lot of aerospace engineers -- she took the government up on its offer and enrolled in a class in hypersonic theory at the University of Maryland. The concepts made sense to her, she says, because her academic background made her so familiar with the chemical physics effects that were essential to them. The aerospace engineers, in contrast, were more comfortable with classical physics-based fluid dynamics.
“I have an optimistic, can-do temperament,” she said, “sometimes overly so. I was confident that I was going to be able to grasp the fluid concepts and move ahead in the field. I was right in the end, but it was a lot harder than I thought. And I certainly never expected hypersonics to become my career.”
Still with IDA, Levin began researching and publishing papers in the early 1990s, eventually joining the research faculty at George Washington University in Washington, D.C. In 2000, she brought her chemistry and molecular physics expertise to Penn State as an associate professor of aerospace engineering. In 2007, she was promoted to full professor. Besides research and teaching responsibilities, she serves as an associate editor of The Journal of Thermophysics and Heat Transfer.
Levin and her husband have four children, the youngest a student at the University of Virginia. Along with their cocker spaniel, Bob, they divide their time between houses in State College and Alexandria, Virginia. Her husband and she are avid sailors on the Chesapeake Bay, Md.