Space odysseys

An artist's concept of what a solar sail would look like

High-concept sail may propel craft
to places they've never been before

In this story:

Many worlds of possibilities
How to sail to the stars
On the fast track
Miles of sail squashed in a tiny can

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By Christy Oglesby
CNNfyi Senior Writer

(CNN) -- A sail -- twice as wide as the Louisiana Superdome and as thin as a raisin stretched a yard wide -- could allow spacecraft to make journeys that haven't been made before.

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Within the next few decades, NASA scientists hope to develop such a sail that would use energy from the sun, not fuel, to propel spacecraft five times faster than they can move now.

It's an all-around improvement for probing outer space. The fuel, using energy from the sun's photons, would be free. The vessels with a sail would move much faster, traveling at 1,395 million miles per year instead of 279 million. If developed, this method should make journeys possible heretofore considered too costly or too slow.

"The sail would give us the opportunity to do orbits not possible with chemical propulsion, such as an orbit perpendicular to the Earth's orbit," said Paulette Liewer, a physicist at NASA's Jet Propulsion Laboratory in Pasadena, California.

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Spacecraft now move around the sun in an east-to-west fashion, along what might be an equator. A perpendicular orbit would move from top to bottom over the north and south poles of the sun, thus providing new glimpses of that celestial body.

"We've never seen the north pole of the sun," Liewer said.

That polar orbit would be just the beginning of possibilities. If scientists are able to develop the sail, there are many other missions that would be possible or enhanced by that technology, said Dick Wallace, an engineer at the Jet Propulsion Lab.

A few potential examples include trips to Uranus, Neptune and Pluto. Wallace said such a sail would also expedite sample return missions to Titan, the large moon of Saturn, and the large moon of Neptune. Sample return missions involve landing on the body, collecting material and returning to Earth.

Another possibility includes using the sail to venture outside of the solar system to conduct interstellar probes, or to gather material from the space between stars.

Liewer and others want to search interstellar space for evidence of organic matter, part of their larger study on the interaction between interstellar space and the solar system.

"One of the big science questions is, 'How did all the material in the universe evolve,' " Liewer said. "Probing those regions might help answer that question."

The sail is just one method that could propel spacecraft, Wallace explained. Other options include nuclear propulsion and solar electric propulsion.

The sail, however, carries attractive benefits, including lower costs, reduced flight time and the ability to deliver a heavier than usual payload.

"All of this would depend on if the sail were available, and now it's not," Wallace said. "We're talking the far distant future, 2015 plus."

Solar sails would require a thinness that rivals cellophane, the strength to withstand intense solar heat and barrages of micrometeors and an extremely large surface area -- 440 yards (402 meters) wide, roughly twice the diameter of the Louisiana Superdome. A highly reflective coating would harness the momentum of photons streaming from the sun.

Constructing the sail is daunting but doable, NASA scientists said. Researchers believe they're close to breakthroughs with lightweight composites, including a carbon fiber material developed by Energy Science Laboratories in San Diego. Its density is the equivalent of a raisin flattened to one square yard (0.8 square meter), according to NASA.

"It looks like it has the right thermal properties, so it can go near the sun and not overheat," said Les Johnson, manager of Interstellar Propulsion Research at NASA's Marshall Space Flight Center in Huntsville, Alabama.

The sail gets its energy from photons, or measures of electromagnetic radiation. As those photons bounce off the sail, they create energy. That energy and radiation pressure propel the sail.

To generate serious speed, a sail probe must first travel to the vicinity of the sun, where it juices up on solar photons. On its way out of the system, it would cast off the sail near Jupiter, where the stream of sun particles peters out.

"All of the thrusting is in the inner solar system, then it coasts," Johnson said.

Voyager, a probe that uses chemical propulsion and planetary gravity assists, was launched into space in 1977. It continues to beam back scientific information. But Johnson said its instruments are not ideal for collecting the kind of data that deep space scientists need.

A probe with a solar sail launched in 2010 and traveling at 150,000 mph (km/h) would pass Voyager in 2018 -- despite the fact that the latter would have had a 41-year head start.

Ultimately, solar sail-enabled spacecraft could travel more than 23 billion miles (37 billion km.), or 250 astronomical units (AUs), said Johnson. One AU is 93 million miles (150 million km.), the distance between the Earth and sun.

Liewer said current probes travel about 3 AUs per year. The sail might be able to move at 15 AUs per year.

"Now if you launch with conventional propulsion, most of the scientists would be retired or dead" when such a probe reached its target distance, Johnson said. But even at such a vast range, the probe could beam back transmissions to Earth in several hours.

Creating a solar sail is difficult enough, but hoisting it could prove an even greater feat.

"I am confident that we can get the materials, but packaging and deployment will be the biggest nut to crack," Johnson said.

Jet Propulsion Lab scientist Robert Frisbee, who studies advanced propulsion concepts, foresees major challenges ahead. "We have miles of sail that must be squashed inside an itty-bitty can and placed in a launch vehicle," he said.

Liewer estimates that the container would be the size of a garbage can.

Because of atmospheric drag, a NASA spacecraft would have to travel hundreds of miles from Earth before it could unfurl a solar sail, Frisbee said.

Space scientists are considering several methods to deploy a giant sail, he added.

One would be to fold the material like a sheet of paper, then extend it out with mechanical booms. Another is using an inflatable structure, such as a long balloon, that inflates with a tiny amount of gas and in so doing pulls out the sail.

According to Johnson, decades after solar sails ply the celestial seas, they could rely on more than the sun for power. Lasers or microwave beams, perhaps originating from satellites placed strategically around the solar system, could give spacecraft critical boosts on journeys to the stars.

CNN Interactive Staff Writer Richard Stenger contributed to this report.