NASA is getting ready to ride the “winds” of space on sails lighter than gossamer, yet large enough to cover a small field. The space agency’s Solar Sail Demonstration, also known as the Sunjammer Project, may launch as early as 2014 when it will send the largest solar sail yet built into orbit, to demonstrate the technical viability of the device.
Sunjammer and the term “solar sailing” were coined by Sir Arthur C. Clarke in his 1964 short story, The Sunjammer. It’s an idea that goes back to Johannes Kepler, though it was James Clerk Maxwell whose theory of electromagnetic fields and radiation showed that a sail could be pushed by sunlight.
It’s an unbelievably tiny push, so the payload must be very small and the sails very large and light, but over time it can really add up. A typical spacecraft on the way to Mars can be pushed as much as 1,000 kilometers during the journey even without solar sails. NASA’s Messenger probe, for example, used its solar panels as sails for making course corrections.
The basic design of a solar sailing spacecraft is an ultralight mirrored Mylar sail controlled by spider thread-like lanyards, that is propelled by the pressure of light from the sun. The term solar sailing is apt because the principle is exactly the same as with nautical sailing, with the same maneuvers of tacking, luffing and running before the "wind." The hard part is coming up with a design that is light enough to be pushed by sunlight, yet that can maintain its shape without collapsing, so solar sails tend to be either web-like affairs or spun to keep their shape through centrifugal force.
In Sir Arthur’s short story, the solar sails were used to propel manned space yachts in a race around the Moon. NASA is much less ambitious. The Sunjammer’s "In-Space Demonstration of a Mission-Capable Solar Sail" is intended simply to test the feasibility of solar sails, and the design of the unmanned craft reflects this. It’s seven times larger and weighs ten times less than previous solar sails. Measuring approximately 124 feet (38 m) on a side, it covers almost 13,000 square feet (1207 m²) or a third of an acre. Despite this, it weighs only 70 pounds (32 kg) and collapses to the size of a dishwasher. It uses vanes for attitude control, and the total force that it’s designed to deal with is only about 0.01 newton – or around the weight of a packet of artificial sweetener.
Sunjammer is being built by L'Garde Inc. of Tustin, California in association with the National Oceanic and Atmospheric Administration. Its design advances on 2005-2006 vacuum chamber ground tests by L’Garde at NASA’s Plum Brook Facility in Sandusky, Ohio, and the deployment of the 100-square foot (9.2 m²) NanoSail-D sail in Earth orbit in early 2011.
The Sunjammer will go into Earth orbit as a secondary payload on a Falcon 9 rocket. Once in orbit, the Sunjammer will unfurl its sail and then it will go through its paces as the attitude controls, sail stability and trim are tested and a navigation sequence is executed.
According to NASA, the Sunjammer technology is suitable for a wide range of missions including deployment of space weather systems to warn satellites of solar storms, and as a means of cleaning up space debris, hovering at high altitudes, and propelling deep space missions.