Setting sail for outer space is no pipe dream

THE CONCEPT of solar "sails" - giant, reflective panels harnessing the sun's rays for interplanetary and even interstellar propulsion - has long been the stuff of science fiction. Within the next few weeks, however, the feasibility of "space clippers", using sunlight to ride the spaceways, will be put to the test, when a Russian submarine in the Barents Sea launches Cosmos 1, the first solar-sail spacecraft.

Cosmos 1 is also the first international, privately funded space mission and is being carried out by the Pasadena-based Planetary Society, the world's largest grassroots space interest organisation, in conjunction with Russia’s Space Research Institute and NPO Lavochkin in Moscow, which has built the unmanned space vehicle. After several postponements, it is now expected to take off within a month, with a launch date to be announced within days.

Carried into orbit 800km above the earth by a Volna rocket - a converted Soviet missile - Cosmos 1 will inflate tubes to unfurl eight 15-metre-long, triangular mylar sails in a giant windmill configuration, giving a total sail area of 600 sq metres. These sails are expected to gradually raise the craft’s orbit, as they catch light particles. The vehicle will be visible to the naked eye as it circles the world, its sails reflecting sunlight. The sails are expected to start deteriorating within a month and it remains to be seen whether the vehicle stays in orbit indefinitely or burns up on re-entry.

Ground tests or simulations can offer no clue as to how the spacecraft will behave once the massive, but ultra-thin, sail area is deployed, says Dr Louis Friedman, project director and a co-founder of the Planetary Society with the late Carl Sagan, the visionary astronomer and author. "We don't know how the vehicle will behave dynamically in weightless conditions and in a vacuum," says Friedman. "It could oscillate, even rip apart; or it could spread wide and sail effortlessly on these beams of light, as we hope it will."

Last year, a Japanese rocket succeeded in unfurling two space sails, although they didn’t go into orbit. The Planetary Society attempted a similar experiment in 2001, but the payload failed to separate from the rocket.

Contrary to common belief, space sails do not harness the "solar wind", which flows from the sun but exerts very little force. Propulsion comes from the pressure of photons (light particles) from the sun (or, conceivably, from an artificial, satellite-mounted laser source). Compared to a conventional rocket, a solar-sail craft will accelerate very slowly at first, but will continue up to the kind of speeds which, some specialists argue, might some day offer a means of interstellar travel.

Cosmos 1 has cost $4 million - bargain-basement prices in astronautical terms - by resorting to cut-price technology such as the former Soviet missile as carrier and the submarine launch. The main financier is Cosmos Studios, the science-based entertainment corporation whose chief executive is Sagan’s widow and former collaborator Ann Druyan.

Asked how he feels now that this project is reaching its climax, Friedman replies: "A crazy mix of sweaty palms from nervousness and pride that we have made it to countdown. Space is not about the 100,000 things you do right but about the one that you do wrong. "

He visualises solar-sail technology as providing "a workhorse for going back and forth to the planets", adding: "We would like to advance a mission that could fly into interplanetary space and perhaps experiment with space-based searches for extraterrestrial intelligence."

Looking on with interest is NASA, which has been ground-testing a 20-metre solar sail at its Marshall Space Flight Centre, and will have access to Cosmos 1’s flight data. Also watching, from Glasgow, is a leading authority on solar sails, Professor Colin McInnes of Strathclyde University.

"Good luck to them," he says. "It’s a huge effort on the part of the society and the Russian contractors, and it will be very interesting to see what happens for a number of reasons, both as an experiment in solar sailing and a privately financed venture."

McInnes was involved briefly in design reviews for Cosmos 1, but has been working on a study for the European Space Agency to identify key missions for which solar sails would be best suited. He suggests that the kind of landmark solar-sail missions the ESA may consider include: a demonstration mission over the next four or five years; further on, a mission to put an un-manned spacecraft in polar orbit round the sun; and an even more ambitious project to spiral another craft close to the sun, then use the increased photon pressure to shoot it out to the "heliopause" zone beyond the edge of the solar system, to sample true interstellar conditions.

McInnes sees solar sailing as filling space travel niches: "It’s a romantic idea but in order to push it forward, you have to identify the practicalities."

As far back as 400 years ago the astronomer Johannes Kepler, observing (inaccurately) that comet tails appeared to be blown by a solar breeze, speculated that, some day, ships might navigate space using this "wind". Writers like Poul Anderson and Arthur C Clarke envisaged "sunjammers" sailing through space. Cosmos 1 will give the first inkling as to whether, once again, sci-fi will become science fact.

• Further information at planetary.org

• For further details, visit planetary.org/solarsail