Sailing through space on a plasma beam

In recent years, NASA has developed a more potent alternative - the ion-drive motor. It flew successfully on the Deep Space 1 mission. The European Space Agency used a similar approach on its SMART-1 lunar orbiter, which this month completed its first orbit around the moon.

But these still leave the burden of propulsion with the spacecraft.

Winglee's team hopes to change that equation by mimicking nature - particularly the way hot, electrically charged gases, or plasma, from the sun interact with Earth's magnetic field. The goal is to allow astronauts to travel in smaller, lighter spacecraft, or to ensure that more of a vehicle's volume is taken up with exploration gear instead of fuel tanks.

For years, researchers have been working on the idea of capturing this solar wind in reflective "sails" made of thin material such as mylar. The advantage: the push on the sail occurs continuously, allowing a craft to build speed to levels unattainable with today's chemical rockets.

In March, the Planetary Society, a space- exploration advocacy group, plans to launch Cosmos 1, which will test the concept. The mission will be launched from a converted Russian missile submarine.

But Winglee and his colleagues reckon that just as the solar wind exerts pressure on Earth's magnetic field, it could do the same for a spacecraft that makes its own magnetic field - turning it into a magnetic sail. Others, such as Robert Zubrin, of Pioneer Astronautics in Lakewood, Colo., have developed a concept for magnetic sails that relies on superconducting magnets to generate the fields. Winglee's group has taken the idea of a magnetic sail a step further with a craft that generates its own plasma. By injecting this plasma into the craft's magnetic field, the field would expand, making the system more efficient.

The team's initial concept involved using the system passively, just as a mylar solar sail would be used. But in developing the lab equipment to test the concept, the team recognized that the plasma "wind" could be provided artificially, through satellites that generate plasma beams. Dubbed MagBeam, the approach would be particularly well suited to traveling to and from other planets, they say. The satellites providing the beams could themselves draw energy from the sun, if close enough, or from small nuclear sources if they were placed in orbit around the outer planets.

The satellite would aim its beam at the spacecraft, which orbits nearby. As it travels, the beam generates its own magnetic field. As the beam nears the craft, its magnetic field couples with the field the craft itself generates, ensuring that the beam will remain "locked" on the craft for as long as necessary to build the needed velocity. The process could be reversed for braking.

Armed with a new pot of money from NIAC, announced last month, the goal now, Winglee says, is "to prove the approach in the lab and develop the scaling arguments" that will gauge the feasibility of building prototypes.

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