Special Report ­ Information Technology

April 1997

		Dust Clouds of Ice   The Space Shuttle often generates electromagnetic puffs of dust, which interfere with communication systems. With the use of supercomputers, Department researchers have been involved in developing the first simulation of this process. The graphs at left show the results over time. When the space shuttle or another spacecraft blasts off from Earth, the rocket exhaust creates a puff of dust in the upper atmosphere, which can interfere with communication and navigation systems. "Every time they turn on the space shuttle engines in orbit, electron density waves are produced that can scatter radio waves used in communications and navigation systems," according to Professor Wayne Scales. "The shuttle exhaust condenses into a dust cloud composed of ice particles, which charge up negatively. This expanding, negatively charged dust cloud then produces electron density waves in the upper atmosphere." Scales and scientists at the Naval Research Laboratory in Washington D.C. have developed the first computer simulation of this process. This sophisticated model is being used to study the physical processes associated with the expansion of a localized dust cloud in space that at present is not well understood. "Once we understand the physics, communication engineers can take this into account in system design. It will become increasingly important as more spacecraft begin to populate space. We can also use this information to track spacecraft in the upper atmosphere. The same density waves that affect communication systems will scatter radar signals, enabling us to follow the craft's path," Scales explained. "This simulation is fairly computationally intense," he continued. "The model incorporates electromagnetic theory and particle dynamics as well as the dust grain charging process. We now use about 10 million simulation particles. We hope to double or quadruple this in the future. "These simulations would be impossible without high performance computers," he said. "You can't get a feel for what's going on by looking at a snapshot in time. These are all nonlinear time evolving processes. With our scientific animation and visualization techniques, many of our results end up resembling video clips." Scales does the number crunching on Department of Defense (DoD) supercomputers, then performs the data analysis and visualization on campus workstations. Most initial production runs, which take 12 or more CPU hours, are done on a Cray C90 - the workhorse DoD supercomputer. Future longer production runs will use the T3D, which is one of the fastest Crays available.

The Bradley Department of Electrical Engineering
Virginia Tech