Saturday, June 6, 2015

After Series of Setbacks, Spacecraft Prepares to Unfurl Sail

from nytimes

A small experimental spacecraft that uses a shiny sail to reflect sunlight to propel itself came back to life Saturday afternoon after a series of near-death experiences. In a rush to finish the mission before anything else goes wrong, the team behind the craft has scheduled the deployment of the sail for Sunday.
The craft, called LightSail, is operated and financed by the Planetary Society, a nonprofit organization that promotes space exploration.
“It’s exciting,” said William Sanford Nye, the society’s chief executive, who is better known as Bill Nye the Science Guy. “It’s anxious. It’s anxiety producing.”
The technology, using sunlight to traverse the solar system in the same way mariners once crossed oceans in sailing ships, is not a new idea, but has not been widely used. While particles of light impart only a smidgen of momentum, the force is continuous and provides propulsion without fuel.
LightSail, packed into a box about the size of a loaf of bread, was one of 10 payloads that last month hitchhiked on a rocket that took an unmanned United States Air Force space plane into orbit. LightSail was successfully deployed and worked for two days before its computer crashed because of a software flaw.
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.
On Wednesday, the solar panels of the spacecraft were flipped up, a prelude to 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.
The LightSail team does not have access to NASA’s worldwide network of radio telescopes but instead relies on two ground stations, at California State Polytechnic University at San Luis Obispo and at the Georgia Institute of Technology.
That means the spacecraft is out of touch when it is not passing over North America. Early Saturday morning, LightSail’s orbit again passed overhead, but it remained quiet until 2:21 p.m. Eastern time.
“We did get a good strong signal from LightSail,” said David Spencer, a Georgia Tech professor who is the mission manager.
On that pass, the batteries appeared to still be offline. “We could read the voltages, but they didn’t appear to be charging,” Professor Spencer said.
Jason Davis, the Planetary Society’s digital editor, reported hopeful progress on Saturday.
On the next orbit, current appeared to be flowing into seven of the eight batteries. “That’s the healthiest we’ve seen the spacecraft since the solar panel deployment on Wednesday,” Professor Spencer said.
He said the problem may be caused by a surge in electrical current when the spacecraft passes from shadow to sunshine.
With LightSail working again, the engineers want to deploy the sail — extending four 13-foot booms and then stretching out 345 square feet of Mylar — as soon as possible.
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On Wednesday, the first step of deployment — the flipping up of the solar panels — was completed. Afterwards, the spacecraft suffered a battery glitch and fell out of touch until Saturday. Deployment of the sail is now set for Sunday.
Professor Spencer said the first opportunity would be around 2 p.m. Eastern time on Sunday, 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. “That would be a riskier operation,” Professor Spencer said, as the maneuver had not been tested on the ground.
Even if deploying the sail is successful, confirmation may not come until Monday, he said.
The sail would bring the mission to an imminent end, probably within two to 10 days. The orbit of the spacecraft is too low to overcome atmospheric drag and demonstrate actual solar sailing.
This flight was intended to wring out issues before a second LightSail is to be launched to a higher orbit — and to that extent, it has been successful.
“Enough problems already,” Mr. Nye said. “Everybody is hopeful the sails will deploy, for crying out loud.”

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