The solar sail and boom system developed by L'Garde Inc. of Tustin, Calif., is fully deployed during testing.
NASA ground-tests solar sails for space
By Martin Burkey
DAILY Staff Writer
mburkey@decaturdaily.com · 340-2441
HUNTSVILLE — Marshall Space Flight Center engineers and their industry partners have finished ground tests on a pair of futuristic solar sails that one day could push spacecraft around the solar system with nothing but sunlight.
Solar sails are a staple of science fiction, from the 1800s to a recent "Star Wars" movie.
NASA/Marshall Space Flight Center Photo
Blue lights beneath the system help illuminate the four triangular quadrants of the solar sail developed by ATK Space Sysems of Goleta, Calif.
In reality, packing up a thinner-than-paper sail — perhaps hundreds or thousands of square meters — into a container small enough to be launched into space efficiently and then deploying it without tearing it is harder than it appears in the movies.
NASA officials said both sails, which used different materials and different deployment methods, succeeded with no problems, and they called the tests a critical milestone in putting solar sails to practical use.
As a canvas sail uses wind to push a sailing ship, solar sails are powered by sunlight. When the light reflects off a sail made of material 40 to 100 times thinner than a sheet of paper, the energy from light particles known as photons is transferred to the sail. It's an incredibly small push, but it's a continuous push, enabling a sail to reach 100,000 mph, hover, or do other maneuvers with no onboard fuel.
NASA's two 65-by-65-foot experimental sails look like large thin pieces of aluminum foil supported by a thin framework. The two competing builders were ATK Space Systems of Goleta, Calif., and L'Garde Inc. of Tustin, Calif. The tests were conducted in the world's largest space simulation chamber at NASA's Glenn Research Center in Ohio. It can simulate both the vacuum and temperature extremes in space.
L'Garde's Mylar sail used an inflatable frame that was heated before inflation and then became still in cold space conditions. ATK's sail used a coiled graphite boom to support an aluminized, temperature-resistant material called CP-1 produced by SRS Technologies of Huntsville.
Marshall engineers are interested in solar sails as a way to reduce the cost, weight and travel times involved in future space exploration. The tests this year were the largest sails ever to undergo deployment testing, said Edward E. Montgomery IV, technology area manager for solar sail propulsion at Marshall.
"We went through deployment with motors and gears, all the functionality a solar sail would need," he said. "The size, 20 meters, is larger than has been done anywhere else before. It is important for us to test on the ground in as relevant an environment as we can, before we go to space. We were really just finding out the things we don't know. I could give you a long list of things that might have happened. All mechanisms when very cold have a tendency to freeze up. In particular-electrical charges and static charges build and dissipate differently."
Compact packing
For instance, in order to be launched from Earth, giant sails would have to be folded many times and packed up in a small area. Air escaping into space during launch could create a bubble that would rip the flimsy sail material, he said.
Practical applications would require still larger sails, perhaps 500 feet on a side, he said. But NASA's test chamber is the world's largest and it could only hold a 65-foot-wide sail.
On the ATK design using CP-1, the booms used to deploy the sail were composite trusses like fishing rods that deployed like coiled springs. The L'Garde design used Mylar sails, similar to an inflatable party balloon but much thinner, attached to inflatable booms like giant party horns.
The first mission for a solar sail could be a warning satellite stationed between the Earth and Sun to warn of solar storms, Montgomery said. A satellite that does that job now is at the end of its operational life. A 100-meter solar sail at the right place could increase the warning time from 30 minutes to two hours, he said.
A second possible mission is to send a scientific satellite into orbit around the Sun's poles, a mission that would normally require a lot of conventional liquid fuel, Montgomery said.
NASA is still considering whether to use solar sail technology on those missions, Montgomery said.
NASA already has competition. The Planetary Society funded construction of a solar sail spacecraft in Russia. It was supposed to go into space atop a Russian submarine-launched rocket on June 21, but the rocket engine failed before the spacecraft reached orbit. The space-interest group vows to rebuild and launch on another rocket.
