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December 31, 2001

Pulsating ‘space hairs’ could help small satellites dock with their mother ship

Beds of thousands of tiny pulsating artificial “hairs” can provide a precise method for steering small satellites to docking stations on larger vessels, according to a study led by researchers at the University of Washington.

The technique is inspired by biology, patterned after the action of the small hairs, or cilia, that line the windpipe and keep it clear of mucus. It could come into wide use in future space missions as technicians begin to deploy swarms of “picosatellites” – spacecraft small enough to fit in the palm of one’s hand – to do maintenance, repair and observation work for larger satellites or space stations, according to Karl Bohringer, assistant professor of electrical engineering and leader of the effort to adapt the technology for use in space.

“Such small satellites will have to dock frequently and quickly for refueling or to download data,” Bohringer said. “This appears to be a very quick, efficient way to accomplish that. In addition, the space cilia are lightweight and relatively low cost.”

The research is featured in the latest issue of the journal Smart Materials and Structures.

The microcilia were originally developed by Gregory Kovacs and John Suh at Stanford University with funding from the Defense Advanced Research Projects Agency. Suh currently works for Xerox Corp. in California. Bohringer and his team’s research involves adapting the cilia for use in space.

In creating the devices, Suh deposited layers of a polymer on a flat silicon plate and then, using micromachining processes, carved out units, or cells, containing four cilia each. The cilia are just 0.5 millimeters (two hundreths of an inch) tall, and each cell resembles a diminutive four-leaf clover.

Each cilium contains a titanium-tungsten heating element. When at rest, the cilia curve up and away from the silicon plate, but when current is applied to the heating element the cilia are forced to flatten. By turning cilia facing the same direction on and off in sequence, Bohringer can prompt them to act like thousands of tiny fingers that move in pulsating waves to nudge objects in any of eight directions.

Bohringer, UW graduate student Mason Terry and recent graduate Joel Reiter tested the cilia’s potential using an air table to simulate the weak gravity of space and a small aluminum block as a picosatellite (a satellite weighing less than a kilogram, or a little more than two pounds). In experiments, the cilia arrays were able to easily and precisely maneuver the block. Bohringer calculates that a patch of cilia 50 centimeters (20 inches) across would be adequate to steer a 40-kilogram satellite.

The one downside, he said, was that the process used more electricity than he would have liked. However, he is confident that can be addressed with some design changes.

“We’ve shown that this is workable, which is the important thing,” he said. “Now we’ll just have to wait to see if this is the direction agencies like NASA and the Air Force want to go.”

Funding for the project was provided by the Air Force and the Universities Space Research Association.

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For more information, contact Bohringer at (206) 221-5177, (206) 543-2150 or karl@ee.washington.edu.

A high-resolution close-up of a microcilia cell is available on the Web at www.washington.edu/newsroom/news/images/cilia.jpg. Photo credit should go to John Suh. An electronic copy of the article can be found on the Smart Materials and Structures Web site at http://www.iop.org/Journals/sm