In the history of exploration, nothing looms quite so large as the unfurled sail, billowing with wind and striking out for destinations unknown.
Now, the Pasadena-based Planetary Society is planning to start sailing through the cosmos, literally. This fall, the group of space enthusiasts will launch the world's first solar sail mission. It is the first privately funded space mission launched to develop space technology.
The mission is resurrecting an 80-year-old dream--and a technology first embraced, then abandoned, by NASA. The goal is to create spacecraft that can travel for trillions of miles to distant stars without carrying fuel.
The mission will basically test the sails' performance 850 kilometers above Earth. It is just a small step to see if sails can be unfurled and steered in space. But this may one day be the way we travel beyond our solar system.
"The way to the stars . . . that's the irresistible lure," said Lou Friedman, the society's executive director.
Solar sails are huge, extremely thin sheets of reinforced, aluminized Mylar that act as mirrors and are pushed gently by the force of the sun.
When photons, or particles of light, hit an object, they push on the object's surface. When light reflects off an object, it pushes twice as hard. This gentle push is what causes the sail to move. The sail can be steered by changing the angle at which it faces the sun.
"It's basically Einstein's E=mc2 in its purest form," said Friedman. "Light carries energy and, as soon as you hit the sail, it transfers into momentum."
(This is different from the solar wind--the ions, protons and electrons that flow from the sun to Earth and can disrupt communications on Earth.)
Although light provides only small amounts of acceleration compared with that of a rocket engine, that acceleration can increase over time to hundreds of thousands of miles per hour. "And it doesn't require fuel," Friedman said.
For Friedman, 60, the mission is a trip back to his roots. A mathematician and aerospace engineer by training, he spent 10 years at NASA's Jet Propulsion Laboratory, working on some of the biggest planetary missions of the 1970s. He was also in charge of JPL's $4-million solar sail program and helped plan a solar sail mission to rendezvous with Halley's comet. NASA gave up on the project in 1977.
"It was tough," Friedman said of the cancellation. "It was premature. It was a tremendous disappointment."
Friedman continued to see solar sails as key to long-distance space exploration after he took the helm of the Planetary Society in 1980. He wrote a book, "Starsailing: Solar Sails and Interstellar Travel," in 1988. But he abandoned the notion of ever working on a solar sail mission again.
Early last year, though, a team of engineers from Russia's Babakin Space Center, which develops commercial ventures, approached Friedman with an idea for a low-cost solar sail. Because it was a practical plan--and a cheap one at $4 million--Friedman took a second look, became interested and found a private donor.
The mission will be funded by Cosmos Studios Inc., an Internet and entertainment venture led by Ann Druyan, the widow of astronomer Carl Sagan, who helped found the Planetary Society. The company, in an effort to provide "entertainment inspired by science," hopes to market images from the flight as entertainment. The spacecraft is dubbed Cosmos I.
The core of the spacecraft will be tiny--less than three feet across and svelte at 88 pounds. But the sails will be spectacular four-story lengths of Mylar flowing from the center of the spacecraft. Blueprints are available at http://www.planetary.org. The craft will be as bright as the moon in the night sky and should be visible from Earth, but Friedman said he is not sure yet if it will be visible from Los Angeles.
The spacecraft will be carried on a Russian Volna rocket, a converted ICBM launched from a nuclear submarine in the Barents Sea north of Murmansk. That way, the mission can be launched for less than $1 million. U.S. ground-based launches can cost 20 times that.
At launch, the thin sails will be tightly coiled within the spacecraft. In space, they will unfurl in about five minutes--"like a New Year's Eve noisemaker," Friedman said.
The sails are reinforced to minimize any tears caused by encounters with space rocks or debris. Solar sailing is becoming possible only because of newly developed ultralight materials that can be used as sails.
The mission takes advantage of inflatable space technology that the Russian engineers have been developing for another client. The "masts" for the solar sail will be long polyester tubes that fill with helium gas to expand.
Unfurling the sails--a technical challenge in itself--will be tested on a launch set for next month and involving only two sails. The larger mission, with an eight-sail spacecraft, is scheduled for October or November.
Solar sails can also be powered by lasers or microwaves--a handy technique for use in distant reaches of the solar system with fewer photons from the sun. Friedman hopes also to use military lasers to propel the spacecraft to greater speeds.
After NASA pulled the plug on funding for solar sails in 1977, work on the technology continued on an informal basis, with financial boosts from the nonprofit World Space Foundation.
In 1993, the Russians successfully unfurled a 60-foot sail in space as part of a scheme to light northern Russian cities through the dark winter. A venture between the German and European space agencies plans to launch a sail into space in about five years. With interest increasing, NASA funded solar sails again for the first time this year, to the tune of $1.5 million. That funding is expected to double next year.
"NASA has a number of missions we'd like to do that really need solar sails," said Hoppy Price, who manages the solar sail technology program at JPL. Plans include interstellar missions in the distant future.
Solar sails could be used to improve early warning systems for solar flares and other space weather phenomena. Sails could also offer new orbits for communications satellites, allowing them to hover over the poles and northern latitudes instead of over the increasingly crowded equator.
Though NASA is interested in the technology, it does not plan to run a test mission until 2005. NASA missions, explained Price, are generally long-duration, low-risk and filled with scientific objectives. Solar-sail technology is not yet at that point.
The Planetary Society's mission is expected to last only a few days or weeks and will not carry the battery of instrumentation used on a NASA mission.
"It's a very Russian attitude, not an American attitude," Friedman said. "Take a small step and build on it. NASA could never make that limited objective."
But Friedman fervently hopes that his small mission will goad NASA or the European Space Agency into speeding their development of more impressive solar sails.
NASA will be watching every step of the mission, Price said. "I certainly hope they're successful," he said. "The sailing ships of old definitely opened up the world to exploration. Now I see sails opening up the solar system."
McFarling can be reached at firstname.lastname@example.org
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Solar Sailing Through Space
This year, the Planetary Society will attempt to deploy a solar sail spacecraft in outer space. Solar sails are extremely large, thin sheets of aluminized Mylar that can be unfurled in space to harness the gentle power of the sun's rays for movement. The society's spacecraft weighs just 88 pounds, and contains eight very light sails that are each over 50 feet tall. How a full mission would be accomplished:
* Turning sunlight into propulsion
Sunlight is made up of photons. When they hit an object they exert a gentle pressure, or push, on that object. When they hit a mirror or a reflective surface like a Mylar solar sail, they are reflected, causing a slightly greater push than if they were absorbed.
Because the force exerted by each photon is minuscule, huge solar sails must be used to capture enough photon pressure to move the vehicle forward.
Source: The Planetary Society