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.

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