Machine Design

Riding mag-beams to Mars

A new propulsion technology for space vehicles, magnetic plasma beams, is being investigated by Robert Winglee at the University of Washington.

Ian Smith works on a plasma chamber which simulates spacelike conditions for testing mag-beam prototypes.

A high-power helicon, an electrodeless plasma thruster, can run at hundreds of kilowatts to produce thrust levels as high as several Newtons. It is the type of thruster that could be powered by remote plasma generators.

If successful, it promises to make round trips to Mars into 90-day excursions rather than 2.5-year voyages, which is what it would take using conventional rocket technology.

The concept relies on a series of space stations sending out streams of magnetized ions (i.e., a plasma). Magnetic sails on a spacecraft would use the plasma beam, much like a sailboat uses the wind, to propel itself through space. Ideally, a similar space station at the craft's destination would also send out "mag beams" that would slow craft during their approach. Winglee estimates that a 32-ft-diameter beam could accelerate a spaceship to 26,000 mph, or 625,000 miles per day.

The system uses magnetized plasma beams because which lets engineers steer them and eliminates instabilities found in unmagnetized plasmas. Winglee estimates that if the sails are thousands of square meters in surface area, pointing accuracy need be no tighter than 3°. Although it would take electricity measured in megawatts to create such a beam, the beam itself would have less energy than other low-level radiation hazards in space. So there would be no danger to spaceships or satellites that accidentally cross the beam, but communications could be disrupted.

The system's major advantages are that it surpasses the speed limit of chemical propulsion by an order of magnitude and it separates the power source from the spacecraft. This means spaceships will not have to carry heavy engines and fuel loads, making them less expensive to build and maintain. The downside is that it would take several billion dollars, along with years of R&D, to develop and deploy space stations capable of sending out mag-beams. But once in space, the stations could be powered by solar energy if close to the sun, nuclear energy if too far out, and last indefinitely. They could serially power several ships at once and speed up or brake ships, as the case may be.

Winglee and his team (and he's looking for EEs) are using a $75,000 grant from NASA's Institute for Advanced Concepts to validate the concept and identify challenges over the next five months. He hopes his project gets through the next phase with NASA, which would garner his team $400,000 over the following two years. "A mag-beam test mission could be possible within the next five years if support remains consistent," says Winglee. "The technology would facilitate a permanent human presence in space, which is what we are trying to get to."

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