Solar Sailing Spacecraft Back to Life, Set to Deploy Sail Despite Failures

The solar sail spacecraft LightSail is set to unfold its sail.

Its deployment is scheduled for 2:02 pm EDT (Eastern Daylight Time), which is 6:02 GMT (Greenwich Mean Time), if battery levels continue to trend stably during Sunday’s early morning ground station passes, according to Jason Davis, the Planetary Society’s digital editor.

Solar sails use the sun’s energy as a method of propulsion—flight by light, similar to the way sailing ships make use of the wind.

Solar sail spacecraft capture light momentum with large, lightweight mirrored surfaces—sails. As light reflects off a sail, most of its momentum is transferred, pushing on the sail. The resulting acceleration is small, but continuous. Unlike chemical rockets that provide short bursts of thrust, solar sails thrust continuously and can reach higher speeds over time.

The LightSail, operated by The Planetary Society, the world's largest non-profit space advocacy group, was launched on May 20, but on May 22 the spacecraft, which is about the size of a loaf of bread, went silent.

The Planetary Society suspected that a software glitch had caused the flight system to crash once it had collected more than 32 megabytes of data.

Eight days of silence followed until, as engineers expected, a high-speed charged particle zipping through space fortuitously scrambled part of the computer’s memory and caused the computer to restart.

Then the solar panels of the spacecraft were flipped up, in preparation for the sail’s deployment. But then the batteries suffered a glitch that knocked them offline, with no current flowing in or out. And LightSail fell quiet again.

Jason Davis said the problem may be caused by a surge in electrical current which occurs when the spacecraft passes from shadow to sunshine.

Now, he says, LightSail's batteries appear to be receiving current from its panels – which needs to happen for its sails to open.

The engineers now want to deploy the sail as soon as possible; they will extend four 4-meter booms and then stretch out the sail's 32 square meter surface.
The first opportunity would be therefore when the craft is in contact with a ground station and when it is in sunlight and can thus draw power from the solar panels.

The team would go ahead with deployment even if the batteries were offline again.

Even if deploying the sail is successful, confirmation may not come until Monday, according to Professor Spencer.

The sail would bring the mission to an end, probably within two to 10 days. The orbit of the spacecraft is too low to overcome atmospheric drag and demonstrate actual solar sailing.

The first mission comes as a test flight that will pave the way for a second, full-fledged solar sailing demonstration in 2016.