Innovations: A good hair day in space
EE researcher’s work named among top 100 stories by Discover Magazine
- Microcilia under a microscope
Electrical Engineering Assistant Professor Karl Bohringer thought he had a good idea about how to use beds of thousands of tiny, pulsating artificial “hairs” to manuever small spacecraft into docking position.
Discover Magazine agreed, naming his research one of the top 100 science stories for 2002. The honor was unexpected, he said, but reflective of the caliber of work done by UW engineering faculty.
The technique, which could also be used to assemble delicate hardware, 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 Böhringer.
“Such small satellites will have to dock frequently and quickly for refueling or to download data,” Böhringer 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 microcilia were originally developed by Gregory Kovacs and John Suh at Stanford University with funding from the Defense Advanced Research Projects Agency. Böhringer and his team’s research involves adapting the cilia for use in space.
In creating the devices, layers of a polymer are deposited on a flat silicon plate and then, using micromachining processes, researchers carve 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, Böhringer can prompt them to act like thousands of tiny fingers that move in pulsating waves to nudge objects in any of eight directions.
Böhringer, 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. Böhringer 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. One possible solution is electrostatically activated cilia, which are in development and could be ready for testing within a year.
Funding for the project was provided by the Air Force and the Universities Space Research Association.