Stove-Top Rocket

Sunday, December 01, 1996
When Michael Micci looks at a microwave oven, he sees not just the means to a ten-minute baked potato but a new way to power satellites. Micci, an aerospace engineer at Penn State, has made the heating unit from an ordinary 1,000-watt microwave oven the heart of a prototype rocket engine he’s building in his lab.

Conventional rockets in space must carry their own oxygen supply, usually in liquid form, to burn their fuel. This can be a costly--and hazardous--affair. To avoid lugging extra weight into orbit, satellites have been built that use electricity instead of combustion to heat and expand the fuel, creating the pressure that forces the propellant out the rocket nozzle. But the fuel itself tends to eat away at the exposed electrodes supplying the electricity, greatly limiting the life of the engine.

Micci’s rocket engine, called the Microwave Arcjet Thruster, avoids such problems. It heats its propellant much as a microwave oven heats up a cold cup of coffee--microwaves generated by an electrically powered oscillating magnet vibrate nitrogen or ammonia molecules, causing them to bash into neighboring particles. All this bashing heats the propellant, increasing the pressure inside the fuel tank so that the propellant shoots out a nozzle in the rear at high speed. The higher your exhaust velocity, the more thrust you get for a given mass of propellant, says Micci.

Microwaves heat food evenly, but Micci’s engine focuses the microwaves on one hot spot near the nozzle. The focused heating creates higher fuel temperatures and pressures at the nozzle, which in turn produce more of a kick to the rocket when the propellant streams out of the nozzle.

Micci is now looking for money to try his engine in orbit. The engine would put out about one-twentieth of a pound of thrust--that doesn’t sound impressive, but it’s typical of engines used to propel small satellites. Considering that propellant problems are the major cause of satellite death, Micci’s thruster should get lots of attention if it performs well. But he says his kitchen rocket may have applications beyond simple communications satellites--solar panels could provide enough electricity to propel a probe to another planet. Once you get into space, he says, you can use this to do anything you want.
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