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Pocket Rockets Pack a Punch

First proposed a decade ago, microrocketry is taking off. Before long, dime-sized dynamos may power everything from tiny satellites to “smart dust.”
May 18, 2001

The rocket ignites. A jet of white-hot flame shoots out below. Its operators increase power and the flame grows-until the rocket explodes in a ball of fire.

Exactly as expected. A dangerous experiment to perform in a lab? Not when the rocket is a dime-sized microelectromechanical system-a so-called MEMS-made of silicon. Laboratories around the country are looking at MEMS rockets and other micropropulsion devices to power a new generation of cheap, tiny satellites and other devices.

Heading for Orbit

The most ambitious project sits in the Massachusetts Institute of Technology’s Department of Aeronautics and Astronautics. With NASA support, MIT engineers are building a microrocket that works more or less like the engine on the space shuttle. NASA hopes to use the microrocket for attitude control on future space vehicles, says Alan Epstein, head of MIT’s Microengine Project.

MIT’s “space cadets,” says Epstein, also want to deploy arrays of microrockets to launch tiny satellites about the size of a Coke can. Networks of “nanosats” could support earth observation or satellite maintenance.

The bottom line for an engine is the amount of thrust it generates relative to its own weight. The space shuttle’s main engine produces a thrust-to-weight ratio of 70. MIT’s microrocket has reached 85, and its builders estimate a potential ratio more than 10 times that-more than enough to launch a satellite into space.

“We’re looking at very high thrust-the high-performance end of microrocket engines,” Epstein says. That is what sets the MIT project apart from microrocket efforts at the University of California at Berkeley, Caltech and elsewhere, he explained.

Epstein says the MIT project is on track to produce a working, integrated microrocket by the end of 2003. The next milestone comes this September, when Epstein aims to build a working MEMS turbopump, a key component that will inject fuel into the rocket’s combustion chamber at very high pressure.

“Right now we have a roomful of equipment that delivers the fuel,” Epstein says. “The turbopump miniaturizes all that” with a fan-like microturbine that pumps fuel into the combustion chamber.

The turbopump under construction is significantly larger than the microrocket itself. To integrate the two-still a distant goal-engineers may take a page from rockets like the Russian-designed RD-170, which fuels four combustion chambers from a single turbopump.

Berkeley Blasts Off

Impressive as it is, MIT’s microrocket still sits on a lab bench. That’s not the case at Berkeley, where engineers at the Sensor and Actuator Center have already launched a more modest MEMS rocket.

The Berkeley microrocket, an advanced version of a “match stick rocket,” is half the size of the MIT device, with an average thrust-to-weight ratio of five.

That’s still plenty of thrust for project advisor Kris Pister. He spearheads an effort to design “smart dust”-millimeter-scale MEMS devices capable of sensing, computation, communication and mobility. “All of my work is focused on making the absolutely smallest vehicles that can be controlled by humans,” he explains.

Networks of smart dust, Pister says, could study a weather system, battlefield, rainforest canopy or any hard-to-reach area.

“We just want to give a sensor the ability to jump up and move around and land,” Pister says. The trick, he says, is deploying the dust. The most promising designs are flat wafers of silicon, a shape that lets them take advantage of solar power but makes for a lousy projectile, due to drag. He explains that an onboard microrocket will propel smart dust much farther than a separate launcher using the same amount of fuel.

The dime-sized Berkeley microrocket flies edge on (“like the Millennium Falcon,” Pister says) for a vertical distance of three meters. The rocket’s theoretical maximum height is closer to 50 meters-high enough, he says, for a device that could drift for miles in the air currents before landing.

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Illustration by Rose Wong

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