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.
