Little levers for satellites: Cilia may precisely dock tiny spacecraft

In an era of satellite design now in its infancy, large and costly spacecraft are giving way to fleets of cheaper, miniaturized satellites. Some may be as small as a deck of cards. One challenge of this approach is designing means to subtly position the spacecraft during their frequent docking maneuvers with a mother ship to refuel or transfer data.

WHISK(ER)ED AWAY. By flapping, these microcilia may maneuver pocket-size spacecraft as they dock. Suh

John W. Suh of Xerox Palo Alto (Calif.) Research Center and his colleagues may have come up with a solution. They’ve demonstrated that artificial whiskers, or cilia, which could be mounted on a mother satellite, are strong and precise enough to move a companion vehicle with great finesse.

Suh says the group’s arrays of microscopic cilia have positioned a satellite-like object to within a few micrometers of a target spot. That’s good news for satellite makers, given that “space cilia are lightweight and relatively low cost,” says team member Karl F. Böhringer of the University of Washington in Seattle. The scientists reported their work in the most recent (December 2001) issue of Smart Materials and Structures.

Originally inspired by wee navigational hairs on various microorganisms,

Böhringer, Suh, Gregory T. A. Kovacs of Stanford University, and their students have been developing cilia since the early 1990s (SN: 7/26/97, p. 62). Unlike biological cilia, the team’s artificial ones are made by coating silicon wafers with a layer of tungsten sandwiched between pairs of silicon-nitride and plastic films. After portions of those five layers are etched away, shovel-shaped paddles remain. They are about as long as day-old whiskers and have built-in, tungsten-based electric heaters, which are used to drive the structures.

Unequal thermal expansion plus contraction of the plastics when heated flexes particular paddles up and down at a rate of up to 60 times per second. Each upward stroke slightly shifts a cilium’s tip horizontally. Consequently, rapid and coordinated flapping of a cilia array can transport an overlying object along.

In simulated microgravity, a set of four cilia chips with just over 1,000 cilia moved an aluminum block about as hefty as a racquetball–and a million times as massive as any of the little cilia themselves.

The cilia “are very nice, because you can move something like on a conveyor belt and place it at some particular point,” comments Volker Saile of the Institute for Microstructure Technology–a joint venture of the Karlsruhe (Germany) University and the Karlsruhe Research Center, a German national laboratory.

One catch, Böhringer notes, is that the heating elements make the cilia power-hungry. Redesigning them to use electrostatic forces might boost the whiskers’ appeal to power-conscious satellite makers, he adds.

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