SAILING IN SPACE ON SUN

Setting Sail Into Space, Propelled by Sunshine
Dennis Overbye, November 9, 2009 (NY Times)

"…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…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…Even as the National Aeronautics and Space Administration continues to flounder in a search for its future, [Dr. Louis Friedman, director of the Planetary Society] announced… that the Planetary Society, with help from an anonymous donor…[will, over] three years… build and fly a series of solar-sail spacecraft dubbed LightSails, first in orbit around the Earth and eventually into deeper space."

LightSail 1. (click to enlarge)

"…[ Ann Druyan, a film producer and widow of the late astronomer and author Carl Sagan, said it is in part for Sagan], who loved the notion and had embraced it as a symbol for the wise use of technology…There is a long line of visionaries, stretching back to the Russian rocket pioneers Konstantin Tsiolkovsky and Fridrich Tsander and the author Arthur C. Clarke, who have supported this idea…The solar sail receives its driving force from the simple fact that light carries not just energy but also momentum…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 5 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.

"Dr. Friedman said it would take too long and involve too much exposure to radiation [for humans]…[T]he only passengers on an interstellar voyage — even after 200 years of additional technological development — [are] 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…[Ii]t can act as an antigravity machine, using solar pressure to balance the Sun’s gravity and thus hover anyplace in space…And [requires little] rocket fuel…[M]any of NASA’s laboratories have studied solar sails…But efforts by the agency have dried up as it searches for dollars to keep the human spaceflight program going…Japan continues to have a program, 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…"

click thru for a complete NASA report on the concept

"[LightSail’s sail] is made of aluminized 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…One of the cubes will hold electronics and the other two will carry folded-up sails…[T]he whole thing weighs less than five kilograms, or about 11 pounds…The LightSail missions will be spread about a year apart, starting around the end of 2010…[ piggybacking] on the launching of a regular satellite…[The first flight will be a brief proof-of-concept]…

"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…For the third flight, Dr. 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. That, he acknowledges, will require a small rocket, like the attitude control jets on the shuttle, to move out of Earth orbit, perhaps frustrating to a purist…"