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Engineers Developing 'Solar Sail' to Power Deep-Space Exploration Vehicles

Posted on: Monday, 22 November 2004, 18:00 CST

Nov. 22--TAMPA, Fla. -- Let's say you want to send a crew of astronauts to Pluto and back.

The first thing you need is enough fuel for a round trip stretching 6 billion miles, but how do you haul all that gas out of Earth's atmosphere? Unless somebody invents a new propulsion system, that trip may never happen.

Well, somebody has.

A team of engineers soon will launch the first solar sail, a craft designed to flow through space much like a sailboat on the ocean. Instead of using wind power, the solar sail rides on waves of sunlight, reflecting solar energy off its mirrorlike material.

If perfected, solar sailing could define the business of long-distance space travel, says Louis Friedman, executive director of The Planetary Society, which plans to launch the first sail in March.

"A solar sail is a propulsion system without propellant," Friedman says by telephone from California. "The real advantage comes when you think of those fuel-intensive missions, of round trips to the planets, where you need fuel for the return home."

The Planetary Society, the world's largest nonprofit space advocacy group, built a device called Cosmos 1. The $4 million, privately funded project involves the Russian space agency, and the spacecraft will blast off atop a ballistic missile launched from a Russian submarine in the Barents Sea.

Cosmos 1 is a technology prototype for flights far into space. The craft will orbit the Earth and make adjustments using nothing more than the "pressure" from photons flowing from the sun.

The National Aeronautics and Space Administration also is working on a sail concept for deep-space missions.

"We are making the stuff of science fiction into reality," says Les Johnson, manager of NASA's In-Space Propulsion Technology Projects Office.

Both programs are based on the same idea: tapping the sun's energy as it flows through space. The sun emits electromagnetic waves that exert a small but measurable force at the Earth's distance -- about 1.3 kilowatts of energy per square meter. When sunlight hits a bright, mirrorlike surface, its photons are reflected. These subatomic particles transmit their momentum to the surface twice; once by the initial impact, and again by bouncing off it.

In the vacuum of space, a solar sail is pushed forward, slowly gaining speed. By changing the angle of the sail relative to the sun, a sail can change direction.

The larger the surface of the ultrathin, ultralight sail, the more solar energy it absorbs. Cosmos 1 is relatively small, standing about 10 stories high. Each of its eight triangular blades is 50 feet long, with a total surface area of 6,500 square feet.

Sails traveling to other planets would need to be gigantic, possibly a mile wide, to catch as much of the fading sunlight as possible.

A disadvantage of the technology is the slow pace of travel in the early stage of a mission. However, because space has no drag, a sail constantly accelerates with the energy flowing from the sun.

Engineers expect the velocity of a typical sail to increase from 195 mph to 2,300 mph over a 12-day period, with top speeds approaching 100,000 mph after three years.

Although NASA's program may be more ambitious, The Planetary Society can set the agenda with a launch in less than five months.

"They don't want to fly without proving the technology," Friedman says of NASA's project. "We're the Kitty Hawk version of the solar sail. We hope our project kick-starts the technology."

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Source: Tampa Tribune

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