Speeding to the solar system's edge.

Could blowing a magnetic bubble into space propel a spacecraft to the edge of the solar system?

Funded by NASA, Robert M. Winglee of the University of Washington in Seattle and his colleagues are beginning to test this novel means of transport in the laboratory.

The design depends upon the interaction between the solar wind--a breeze of charged particles that blows out from the sun--and a magnetically confined cloud of particles. This bubble acts as a miniature version of Earth's magnetosphere, the region around the planet controlled by the terrestrial magnetic field.

Just as the magnetosphere shields Earth from the solar wind, the craft's magnetic bubble deflects the wind. When the swiftly moving solar breeze is diverted around the cloud, it imparts a kick that the cloud transfers back to the spacecraft.

Unlike proposed solar sails, which will get their power from sunlight bouncing off their mirrored surfaces (SN: 8/21/99, p. 120), this means of propulsion does not require special materials or the deployment of huge structures in space, Winglee notes.

Inside a jar-size container on the craft, electrical coils would generate a magnetic field of about 1,000 times the strength of Earth's field. A plasma of ionized helium atoms and electrons that fills the container would then be spewed gradually into space. The expelled particles would drag the magnetic field along, creating a magnetic bubble some 30 to 40 kilometers in diameter that envelops the craft. The researchers plan to produce a bubble 1 m in diameter in the laboratory.

Winglee estimates that just 3 kilograms of helium fuel would keep the magnetic bubble intact for 3 months. He calculates that in that time, a spacecraft weighing a modest 136 kg could attain speeds of 288,000 kilometers per hour.

At that velocity, an airplane would only take about 10 seconds to fly from Seattle to New York. The spacecraft could reach the edge of the solar system in about 10 years. If launched by 2008, it would beat Voyager 1, even though that craft began its journey 22 years ago.

Propulsion expert David Alexander of the Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, Calif., says it could be difficult to steer a magnetically driven craft. He adds that the system might not be well-suited for a long-term mission that requires many changes in direction. Nonetheless, "the big advantage over alternative advanced-propulsion concepts is that it is apparently achievable using current technology," says Alexander.

"[It's] a nifty idea, but we don't know if it will work as advertised until it has been tried out and really blows up [and sustains] a 40-kilometer plasma balloon," says Robert L. Forward of Forward Unlimited in Clinton, Wash.