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Solar-sail mission reflects past and future

The Cosmos 1 solar-sail mission, due for launch this week, builds on centuries of speculation and could help open a new path to the universe beyond. By NBC News' James Oberg.
Artists conception of spacecraft Cosmos 1 set to launch June 21, 2005
An artist’s conception shows the Cosmos 1 spacecraft in flight, reflecting Earth from space.Rick Sternbach / Planetary Society / Reuters

The fanciful idea of sailing through space on a beam of light — the premise for this week's test flight of the Cosmos 1 solar sail — has been around for centuries. But it's only been in the last few years that dreamers have gained the technology to try it out, and the boldness to risk failure after failure until it works.

When it finally does work — if not this time, then certainly someday — all previous methods of space propulsion may seem a lot more primitive and a lot less elegant.

The privately funded $4 million mission is due to begin Tuesday, when a Russian submarine fires a missile bearing the folded-up Cosmos 1 payload into orbit. Cosmos 1 is billed as a totally new kind of spacecraft, but the project's precedents go back almost 400 years, when Johannes Kepler and Galileo Galilei were building the foundations of modern astronomy.

"Provide ship or sails adapted to the heavenly breezes, and there will be some who will not fear even that [outer-space] void," Kepler told Galileo in a letter dated April 19, 1610. Kepler justified the study of astronomy for the benefit of “those who will come shortly to attempt this journey” — a clear vision that was centuries ahead of its time.

If Cosmos 1 works as hoped, it will mark a significant watershed in space propulsion technology first imagined by Kepler, who noted that the glowing tails of comets were blown by what he saw as a powerful wind. Later, astronomers realized that there were actually two distinct "winds" flowing from the sun: the variable stream of electrically charged particles making up the solar wind; and the constant stream of photons, or particles of light.

Contrary to some of the popular conceptions about solar sailing, Cosmos 1 is designed to ride the force of the photons rather than the solar wind. In an effort to head off the confusion over which wind is involved, futurist Eric Drexler proposed 30 years ago that the term "light sail" be used instead — a double entendre that refers to the fact that such sails uses light for power and also must be very light to be effective. Sadly, the poetic and proper term hasn't yet caught on.

The modern concept of using photon pressure to gently but inexorably push spacecraft to high speeds was fleshed out early in the 20th century. However, flexible materials that were light enough, mechanically strong enough, and physically resistant enough to the disintegrating effects of solar radiation just weren’t available until recent decades. As far back as 1960, photon pressure played orbital soccer with the Echo 1 thin-film balloon in orbit, pushing its orbit around with astonishing force until the balloon’s skin shattered. The shards were then flung far and wide by sunlight.

Arguing over history
The California-based Planetary Society has been working on the Cosmos 1 project for five years, with technical assistance from Russian partners and financial backing from Cosmos Studios. The project's leaders claims that Cosmos 1 is "the world's first solar-sail spacecraft" — sparking a debate over just how much of a first it represents. In an odd way, the fact that a debate has arisen over Cosmos 1's future place in history serves as a measure of how realistic the technology has become.

"I am not certain why the Planetary Society makes the claim," Keith Cowing, editor of the independent NASA Watch Web site, said last week. He pointed out that there have been previous solar-sail tests, including a Japanese mission last August during which a small rocket lofted a test payload on a suborbital trajectory and briefly unfolded a solar-sail structure.

Cowing's complaint drew a quick response from Louis Friedman, the Planetary Society's executive director as well as Cosmos 1's program director. He said the Japanese team "did not either build a solar sailing spacecraft or attempt to fly under sunlight pressure. Those latter two goals are unique (thus far) to The Planetary Society project.”

Friedman acknowledged that there have been previous flight experiments with thin-film deployment, but he said none of them actually tried to use sunlight to steer through space.

Indeed, the Russians have twice deployed "sails" from spacecraft, back in the 1990s. One was fully unfurled and reflected sunlight down from the evening skies over central Europe, where it was visible as a bright, fast-moving star. A second deployment failed when Russian Mission Control forgot to retract an antenna out of the way.

Both those efforts were aimed at testing "space reflectors" for ground illumination, and not for space propulsion.

In 2001, Friedman’s group staged a space deployment test flight analogous to last year's Japanese mission. The flight plan called for a quick up-and-down hop with a brief unfurling to test the mechanism. The payload was fired on cue from the submarine, but Russian engineers failed to build a workable deployment system — and the sail, still packed in its canister, never detached from the rocket in flight. The insurance payoff from that failure helped fund this week's flight.

Where do we sail from here?
The extent of Cosmos 1's success or failure may not be known until days or weeks after Tuesday's launch. But if the mission team fulfills its main objectives, Cosmos 1 would merit a prominent place in aerospace history, said Michael Martin-Smith, a British physician, amateur astronomer and member of the British Interplanetary Society.

Martin-Smith has written a book and numerous articles on spaceflight, and has presented papers at annual congresses of the International Astronautical Federation.

“Cosmos 1, of course, aims to do more than demonstrate thrust by solar radiation,” he observed recently on a leading space discussion forum. “It also aims to demonstrate steerability by a process analogous to old-time sail tacking.”

In addition, he said, “if the mission endures, it is planned to use a radio telescope to beam power from here on Earth to add propulsive force as well.”

If those three tasks are accomplished, “it would be fair to claim that Cosmos 1 is, potentially, to interstellar travel what the Wrights' Flyer was to modern aviation — and possibly even over a comparable historical time frame,” Martin-Smith argued.

He is now campaigning for a particular application of space sails that involves not just propulsion but the discovery of potential targets for future exploration, fully consistent with Kepler’s four-century-old vision.

“The looming discovery of Earthlike planets is likely to have an inspirational effect,” he wrote in an e-mail to “There is nothing like a concrete destination, however hard to reach, to focus the dreams of explorers.”

Along those lines, he pointed to a proposal from the University of Colorado's Webster Cash, which calls for the establishment of a giant space-based pinhole camera to seek out and characterize Earthlike planets. This "New Worlds Imager" would consist of a large sunshade with a "pinhole" that would screen out the glare from a distant star and allow a well-placed 40-inch (1-meter) telescope to examine its planets. The assembly would be placed in a stable position far from Earth.

“The engineering problems of transfer, deployment and control of the sunshade bear an uncanny resemblance to the techniques required for Cosmos 1,” Martin-Smith pointed out. So the same technology that enables interstellar flight might also locate and observe the first real targets for such missions, and in much less time than Kepler’s ghost has already been waiting.

James Oberg, space analyst for NBC News, spent 22 years at the Johnson Space Center as a Mission Control operator and an orbital designer.