Sailing through space on a plasma beam

Sitting in the cramped coach section of a transcontinental airliner for five or six hours can be trying enough. But consider NASA's "reference mission" to Mars. Astronauts will be cooped up in their craft for up to six months each way as they travel to and from the Red Planet.

Robert Winglee and his colleagues would like to give these future explorers a break. Inspired by the sun's influence on Earth, the team is developing a unique approach to space propulsion. The craft it envisions hurtles through space on sails made of magnetic fields. The sails billow under pressure from the solar "wind" - electrically charged particles from the sun - or from intense man-made plasma beams, which special satellites would aim at the sails.

These approaches could slash the travel time to Mars from roughly six months each way to 40 days, reckons the group, led by Dr. Winglee, director of the University of Washington's Research Institute for Space Exploration. An unmanned mission to the edge of the solar system itself could be slashed from roughly 40 years to a decade or so.

Winglee says that an 80-day round trip makes it possible to design a Mars mission that would last 90 days, instead of the 950 days that the National Aeronautics and Space Administration uses as its reference or base line for planning. A shorter mission increases its chances of success. "A lot of the technologies we need already exist," he says. "We're just trying to pull them together into something special."

The effort is part of a broader research program NASA is sponsoring through its Institute for Advanced Concepts (NIAC) in Atlanta. The institute is a kind of "skunk works" for the agency, fostering space technologies that won't fly any time soon. In fact, "the enabling technologies may not be available today and the science may not be completely understood," says director Robert Cassanova. But the ideas are conceptually sound, he continues, and hold the promise of revolutionizing space travel over the next 10 to 40 years.

For Winglee - as well as for others working on space propulsion ideas ranging from space elevators and tethers to antimatter engines - the challenge is to overcome the limits imposed by current chemical rockets.

The basic idea behind rocket motors hasn't changed much in the millennium since a pair of Chinese inventors cobbled together the first gunpowder rocket. Modern rockets are tubes loaded with fuel. They sport a motor at one end and a relatively small payload at the other.

In the future, this approach will remain useful for boosting payloads to altitudes where space tethers that look like ferris wheels can grab them and fling them farther, Dr. Cassanova notes. But for routine travel beyond Earth orbit, chemical propulsion grows increasingly impractical. Compared with other techniques, it doesn't give much push for the amount of weight it adds to a spacecraft.

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.