Largest ever space sail for 2014 - it's the Sunjammer!

by Leonard David, Space.com/Sail-World Cruising on 3 Feb 2013 It's not windjammer, it's Sunjammer! Humans learned long ago to push a craft across the water using the wind. Now the pace is picking up as space scientists learn how to push a craft through space using photons from the sun.

The largest solar sail ever constructed is headed for the launch pad in 2014 on a mission to demonstrate the value of what is being called 'propellantless propulsion'.

Dubbed Sunjammer, the giant solar sail measures about 124 feet (38 meters) on a side and boasts a total surface area of nearly 13,000 square feet (1,208 square m, or one-third of an acre). The project is under the wing of NASA's Space Technology Program, within the agency's Office of the Chief Technologist.

NASA has contracted with a team of high-tech 'solar sailors' at L'Garde Inc. of Tustin, Calif., to build Sunjammer.

L'Garde is no newcomer to novel space structures. The company has worked with the space agency on several projects, including the creation of inflatable structures for radio frequency antennas and solar arrays. In 1996, the company flew the Inflatable Antenna Experiment (IAE) aboard the space shuttle Endeavour's STS-77 mission.

Programmatic milestone:
'We took the name Sunjammer from an Arthur C. Clarke short story, a fictional yacht race in the heavens using solar sails,' said Nathan Barnes, L'Garde's chief operating officer and executive vice president, as well as Sunjammer's project manager. Permission to use the name came from the Clarke estate, he told SPACE.com.

Work on Sunjammer this year includes a programmatic milestone — a critical design review — along with a variety of ground demonstration tests and qualification of components, Barnes said. The flight of the solar sail, he said, is set for the end of 2014, to be sent spaceward atop a SpaceX Falcon 9 rocket.

'With this sail, we’re targeting our end goal somewhere in the neighborhood of 1,864,114 miles (3 million kilometers) distance from the Earth,' Barnes said.

A number of test objectives are to be checked off within the first couple months of flight, he added. These include deployment of the sail, demonstration of vector control using sail-tipped vanes, navigation with accuracy and, finally, maintenance of the spacecraft's position at a gravitationally stable location called Earth-Sun Lagrange Point 1.

Sunjammer won't be the world's first solar sail mission, just the largest. NASA launched NanoSail-D, whose sail covered just 100 square feet (9.3 square m), in November 2010. And Japan's Ikaros probe deployed its solar sail in June 2010, becoming the first craft ever to cruise through space propelled only by sunlight.

Neat, clever, exotic orbits:
Sunjammer is potentially applicable to an advanced space weather warning system, which could provide more timely and accurate notice of solar flare activity.

The U.S. National Oceanic and Atmospheric Administration is collaborating with NASA and L’Garde on the upcoming demonstration flight, which will cruise to a spot that provides an interesting view of the sun.

'It will be us flying to a place that a customer actually wants to fly a solar sail to,' Barnes said. 'There are neat, clever, exotic orbits you can do with the solar sail that would permit viewing different portions of the sun that we can’t normally.' [The Sun's Wrath: Worst Solar Storms in History]

One-quarter the size of a football field, Sunjammer will produce a whopping maximum thrust of approximately 0.01 newton, Barnes said — roughly equivalent to the weight of a sugar packet.

Thinner sail:
Kapton is the solar sail material of choice. The mission team worked with chemical company DuPont to produce a special layer of Kapton for Sunjammer just 5 microns thick.

'Thinner is always better,' Barnes said.

When collapsed, the Sunjammer solar sail is the size of a dishwasher and weighs just 70 pounds (32 kilograms).

There are a number of control techniques involved in successfully unfurling the sail, said Billy Derbes, L’Garde’s chief engineer for Sunjammer.

'The highest risk is in the deployment,' Derbes said. A camera attached to the sail will capture the unfurling process.

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