NASA Aims to Set Sail in Space

 Astronomers have long counted on photons to reveal mysteries and wonders of the cosmos. Engineers would like to tap the beams for another purpose: propelling satellites through space.
Though it sounds more like science fiction -- the late Arthur C. Clarke wrote about it in a short story from his collection, "The Wind from the Sun" -- the idea of using the force of light from the sun has been around since the 17th century.

Three years ago, a group led by the privately funded Planetary Society attempted to demonstrate the technology with a project called Cosmos-1, but a botched launch doomed the project.

Now it is NASA's turn.

The agency plans to fly a tiny probe known as NanoSail-D, which is scheduled for launch later this month aboard an experimental Falcon 1 rocket, built by Internet entrepreneur Elon Musk's new startup, Space Exploration Technologies.

NanoSail is not the primary payload and it will be booted off the launcher rather early in the flight. Because the spacecraft will be left in an elliptical rather than circular orbit around Earth, it will be dragged back into the atmosphere as early as five days after launch.

That's not a concern for Edward "Sandy" Montgomery, the NanoSail manager at NASA's Marshall Space Flight Center in Huntsville, Ala., who has been working on solar sail technologies for the past eight years.

"We want to see if the sails deploy in space," he told Discovery News. "This is not a performance evaluation."

Still, a successful demonstration may be enough to convince future spacecraft planners to replace or augment chemical thruster rockets with thin, rolled-up sails that can be unfurled in orbit to catch the sun's light.

The sails, which are extremely thin but strong membranes, are coated with aluminum or another highly reflective surface, so the light can bounce off the sail. The pressure provides a tiny amount of thrust, but it builds up over time.

If the Voyager probes had solar sails, for example, they would have reached the outer edges of the solar system in about a decade, rather than the 30 years it has taken for them to reach their present locations, Montgomery said.

"If you're going far away, the sail will eventually get you there sooner," he said.

Solar sails are most useful where sunlight is strongest -- the inner solar system. With sails, satellites could change orbits, hover and steer themselves out of orbit upon completion of their missions to avoid becoming a hazard to other, still operational satellites.

Rocket fuel for steering thrusters used on spacecraft today is a huge part of a satellite's weight and launch cost. Running out of fuel means the end of a satellite's mission. Then the probes typically linger for decades in orbit.

"Solar sail propulsion, if it achieves its full promise, would enable fundamentally different space missions not feasible or even possible with conventional propellants," said NanoSail's lead scientist Mark Whorton.