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Tiny Tractor Beam Could Keep Satellites in Formation

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Hanspeter Schaub, Gordon G. Parker and Lyon B. King


Ion Space Propoulsion Lab

From Tech Today July 27, 2007

Brad King and Gordon Parker have developed a tractor beam. Now, they’re looking for ways to use it.

“It’s a hammer in search of a nail,” says King, an associate professor of mechanical engineering-engineering mechanics.

The tractor beam is not the sort that could immobilize a Klingon vessel. Instead, it could hold a small group of spacecraft in formation. The device would rely on the subtle electric charge accumulated by objects in space, harnessing forces as small as 10 micronewtons. To put that in perspective, a single paper clip resting on a table exerts a force of about 10,000 micronewtons.

Currently, space technology relies on micro-thrusters to keep spacecraft in place. The problem with these and any other engines is their reliance on a fuel supply, which eventually runs out. And a hundred miles above the Earth is a long way from the nearest fill-up.

King and Parker, a professor of mechanical engineering- engineering mechanics, envision tapping a power source that has always been a major nuisance and, instead, use this power for propulsion. Spacecraft naturally gather an electric charge as they pass through space. Traditionally, this has not been a good thing: static electricity can short out sensitive electronics, wreaking havoc on a spacecraft’s mission. Thus, spacecraft have special systems to shed their electrical charges.

King and Parker’s notion is to use that electricity instead of lose it. Electrically charged objects repel or attract each other, as in pet hair adhering to trousers. By arranging a group of small satellites into a particular crystal formation, it’s possible to tap the energy in static electricity to gently hold each satellite in place and essentially create one functioning unit: the motion of one vehicle affects the entire swarm. Because each of the vehicles is either pushing or pulling on all of the others, the formation has collective behavior. “If you tickle one,” says King, “the whole formation laughs.”

King and Parker call their concept Coulomb spacecraft control, and they have some ideas on what it could be used for.

“It looks like it would be best for high-Earth orbital imaging or deep-space imaging,” King says. An array of small satellites can capture images as clearly as one big telescope or spy satellite, if they orbit in the right formation. “If you have one big satellite and it gets taken out, it’s gone,” he says. “If a single satellite goes out in an array, you still have some functionality. You could even have on-orbit spares waiting to join the swarm and restore the group’s original performance.”

The researchers have not yet demonstrated the concept in space, and that doesn’t worry them. The physics behind the concept “is almost trivial,” they say.

Their main thrust now is finding a target for that hammer. “Half the people we talk with think we’re lunatics, and the other half think it’s an elegant idea,” King smiles. “The nail is to find a killer application, and sooner or later, we will.”


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June 18, 2007