Sailing on sunshine

Space

Sailing on sunshine


Peter Pan would be so happy. About a year from now, if all goes well, a box about the size of a loaf of bread will pop out of a rocket some 500 miles above the Earth.

There in the vacuum, it will unfurl four triangular sails as shiny as moonlight and only barely more substantial. Then it will slowly rise on a sunbeam and move across the stars. LightSail-1, as it is dubbed, will not make it to Neverland. At best, the device will sail a few hours and gain a few miles in altitude. But those hours will mark a milestone for a dream that is almost as old as the rocket age itself, and as romantic: to navigate the cosmos on winds of starlight the way sailors for thousands of years have navigated the ocean on the winds of the Earth.

“Sailing on light is the only technology that can someday take us to the stars,” said Louis Friedman, director of the Planetary Society, the worldwide organisation of space enthusiasts.

Series of solar-sail spacecraft

Even as NASA continues to flounder in a search for its future, Friedman announced that the Planetary Society, with help from an anonymous donor, would be taking baby steps toward a future worthy of science fiction. Over the next three years, the society will build and fly a series of solar-sail spacecraft dubbed LightSails, first in orbit around the Earth and eventually into deeper space.

The voyages are an outgrowth of a long collaboration between the society and Cosmos Studios of Ithaca, N Y, headed by Ann Druyan, a film producer and widow of the late astronomer and author Carl Sagan.

Druyan, who has been chief fundraiser for the society’s sailing projects, called the space sail “a Taj Mahal” for Sagan, who loved the notion and had embraced it as a symbol for the wise use of technology.

The solar sail receives its driving force from the simple fact that light carries not just energy but also momentum, a story told by every comet tail, which consists of dust blown by sunlight from a comet’s core. The force on a solar sail is gentle, if not feeble, but unlike a rocket, which fires for a few minutes at most, it is constant.

Over days and years, a big enough sail, say a mile on a side, could reach speeds of hundreds of thousands of miles an hour, fast enough to traverse the solar system in five years. Riding the beam from a powerful laser, a sail could even make the journey to another star system in 100 years, that is to say, a human lifespan.

Friedman said it would take too long and involve too much exposure to radiation to sail humans to a place like Mars. He said the only passengers on an interstellar voyage, even after 200 years of additional technological development, were likely to be robots or perhaps our genomes encoded on a chip, a consequence of the need to keep the craft light, like a giant cosmic kite.

In principle, a solar sail can do anything a regular sail can do, like tacking. Unlike other spacecraft, it can act as an antigravity machine, using solar pressure to balance the sun’s gravity and thus hover anyplace in space.

At one time or another, many of NASA’s laboratories have studied solar sails. Scientists at the Jet Propulsion Laboratory even once investigated sending a solar sail to a rendezvous and ride along with Halley’s Comet during its pass in 1986.

Halley’s Comet proposal

Japan continues to have a programme, and test solar sails have been deployed from satellites or rockets, but no one has ever gotten as far as trying to sail them anywhere.

Friedman, who cut his teeth on the Halley’s Comet proposal, has long sought to weigh anchor in space. An effort by the Planetary Society and the Russian Academy of Sciences to launch a sail about 100 feet on a side, known as Cosmos-1, from a
Russian missile submarine in June 2005 ended with what Druyan called “our beautiful spacecraft” at the bottom of the Barents Sea. Druyan and Friedman were beating the bushes for money for a Cosmos-2, when NASA asked if the society wanted to take over a smaller project known as the Nanosail. These are only 18 feet on a side and designed to increase atmospheric drag and thus help satellites out of orbit.

And so LightSail was born. Its sail, adapted from the Nanosail project, is made of aluminised Mylar about one-quarter the thickness of a trash bag. The body of the spacecraft will consist of three miniature satellites known as CubeSats, four inches on a side, which were first developed by students at Stanford and now can be bought on the Web, among other places. One of the cubes will hold electronics and the other two will carry folded-up sails, Friedman said. The LightSail missions will be spread about a year apart, starting around the end of 2010, with the exact timing depending on what rockets are available.

‘Kitty Hawk moment’

Friedman said the first flight, LightSail-1, would be a success if the sail could be controlled for even a small part of an orbit and it showed any sign of being accelerated by sunlight. In addition there will be an outrigger camera to capture what Druyan called ‘the Kitty Hawk moment.’

The next flight will feature a larger sail and will last several days, building up enough velocity to raise its orbit by tens or hundreds of miles, Friedman said. For the third flight, Friedman and his colleagues intend to set sail out of Earth orbit with a package of scientific instruments to monitor the output of the sun and provide early warning of magnetic storms that can disrupt power grids and even damage spacecraft. The plan is to set up camp at a point where the gravity of the Earth and sun balance each other, called L1, about 900,000 miles from the Earth, a popular place for conventional scientific satellites.

SOLAR SAIL

* The solar sail receives its driving force from the simple fact that light carries momentum.

* Unlike other spacecraft, a solar sail can act as an antigravity machine, using solar pressure to balance the sun’s gravity.

* The third solar sail will monitor the output of the sun and provide early warning of magnetic storms.

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