Its designers call it LightSail-1. And if it works as advertised, the solar sail project would represent a baby step toward humanity's first starship.
This week, the California-based Planetary Society announced a new project to launch a small spacecraft propelled by a solar sail. In principle, the idea is simple: Use the sail to intercept sunlight, which presses on the sail much like wind on canvas. (The same pressure keeps the sun from collapsing under its own gravity.)
Initially a solar-sail craft builds momentum almost imperceptibly. But with no friction in space to resist its motion, the craft in theory should go faster and faster, as long as there is enough light to propel it. It requires little on-board fuel for course corrections, since the sails can be "trimmed" to change course, just as a sailboat's canvas is trimmed.
Four years after its first solar sail ended up in the ocean instead of orbit, The Planetary Society announced Monday that by the end of 2010 it will try again to launch a spacecraft that will be propelled by the subtle pressure of sunlight.
LightSail-1 is envisioned as the first of a trio of solar sail craft in a project boosted by an anonymous $1 million donation, according to the space advocacy organization co-founded by the late astronomer Carl Sagan.
"It's a low acceleration but it's continuous, whereas a rocket is a high acceleration but it ends quickly," Louis D. Friedman, the society's executive director, said in a telephone interview from Washington, D.C.
Eventually you'll have these missions lasting many years, reaching speeds approaching 100,000 mph, getting out of the solar system in five years instead of 25 years," he said.
The Planetary Society's first solar sail, Cosmos 1, never reached orbit. It was launched in 2005 aboard a converted missile fired from a Russian submarine beneath the Barents Sea. The launch vehicle failed and fell into the ocean.