One of the most exciting new ideas in space exploration is a reincarnation of a very old concept.

Gregory Benford, the 2005 Waynick Memorial Lecture guest speaker, described to a captivated audience of a few dozen people the principles of solar sails.

"The idea behind sails is that you really sail on" the sun's light, Benford said during his lecture, titled "Sailing to the Stars."

"It's a very small acceleration, but the idea is that you sail for free," he said.

Benford, a professor of physics at the University of California, Irvine, is the author of the award-winning science-fiction novel Timescape.

The idea behind solar sail research is to open new frontiers in space exploration, Benford said. Because space sails have to be lightweight by definition, a great deal of them could potentially be put into space at once.

Jérémy Riousset (graduate-electrical engineering), who attended the lecture, said the biggest benefit he could see to using solar sails was the relatively small price tag. "The only reason that they want to do that is because it's cheaper" than rocket-powered space missions, he said.

This would open a door to a less expensive way to explore our solar system, and maybe beyond.

"These are, of course, new ideas," Benford said. "Let's remember that the rocket was invented hundreds of years ago."

Benford said even the idea of sailing through space is not really a new one. "The first Russian sail was conceived about 75 years ago," he said.

He said hundreds of sails have been made worldwide, including in Germany, Russia and the United States.

Benford's presentation included dozens of artists' renditions of spacecraft designed to be propelled by the sun's light. Some were just ideas, while others were sails that have been built but never flown into space.

Most of the sails looked like insects with large, reflective wings arranged in a circle. Others -- mostly the ones that hadn't actually been built -- consisted of a complex system of cables and reflecting sails.

Benford described the physics behind a solar sail: "You bounce these photons like little tennis balls and push [the sail] along."

He said the acceleration due to the reflected light is very small, but it adds up because it is constantly present and because there is no resistance in space.

Likewise, sails and other objects would decelerate slightly if moving toward the sun. "You probably don't notice that you slow down when you walk into the sunlight," he said.

For the last several years, Benford has been working with a team to design a sailing spacecraft, which is scheduled to launch in about a month. The sail is going to be shot out of an old Soviet submarine.

"It turns out this is the cheapest way to put anything in orbit," Benford said.

The sail has a mass of roughly 110 kilograms (or 242.5 pounds) on Earth. By comparison, a typical space shuttle payload is several tons, he said.

Benford said his group had actually built and flown a sail before, but it failed to open in the final stage of deployment.

He said most sails made until now have been made of aluminized mylar, which is lightweight and highly reflective. But very recently, scientists have been considering carbon fiber sails.

"Carbon fiber is light and it resists temperature and it is highly reflective as well," he said. Carbon fiber sails would reflect roughly 90 percent of the light that hits them. The other 10 percent would be absorbed as heat.

John D. Mathews, professor of electrical engineering, organized the event. He said Benford was chosen because of his experience as a scientist, engineer and writer.

"He's an ideal person for the students to meet," Mathews said. "He's everything."

The Waynick Memorial Lecture is an annual event sponsored by the Communications and Space Sciences Laboratory, a part of the College of Engineering.