Solar Sail Spacecraft Set for Launch

Stefan Lovgren
for National Geographic News
Updated June 20, 2005
The Planetary Society, a U.S. nonprofit group devoted to space exploration, plans to launch the world's first solar sail spacecraft tomorrow.

Cosmos 1 will be launched from a submerged Russian submarine in the Barents Sea and carried into orbit by a converted intercontinental ballistic missile (ICBM).

Initially orbiting the Earth at an altitude of about 500 miles (800 kilometers), the spacecraft will gradually move outward by solar sailing—propelled by the pressure of light particles from the sun striking the craft's eight triangular sails.

The journey has no destination. The mission's goal is simply to prove that solar sail technology works.

Space sails carry no fuel and can continue accelerating over almost unlimited distances. This prompts scientists to envision a time when the technology may be used for future travel between planets in our solar system. Someday solar sails might be used to send astronauts to new worlds around other stars.

"This is the only technology known that could lead to practical interstellar flight," said Louis Friedman, the executive director of the Planetary Society in Pasadena, California. "But before that, the idea of going back and forth between the planets without having to carry fuel is a very efficient idea."

Swords into Plowshares

NASA, the European Space Agency, Japan, and Russia all have developed solar sails, but none has yet tried to prove that the sails can propel a spacecraft under controlled flight.

Friedman, who serves as the Cosmos 1 project director, is no stranger to the technology. He headed NASA's solar sail initiative back in the 1970s. That program was ultimately scrapped partly because of financial constraints.

The new mission, budgeted at a mere four million dollars (U.S.), is a privately funded initiative. The price tag is relatively cheap thanks to Russia's low-cost launch system.

The spacecraft will be launched from a Russian nuclear submarine and carried by an ICBM that once belonged to the Soviet military arsenal.

Strategic-arms-reduction agreements between the U.S. and Russia stipulate that Russia must get rid of many of its missiles. Instead of simply destroying them, the Russians have been trying to use up the missiles for commercial purposes, such as the Cosmos 1 launch.

The program "truly signifies the swords-into-plowshares [idea] by using assets designed to destroy worlds to become instruments of scientific progress," said James Cantrell, president of Strategic Space Development, a consulting firm based in Hyde Park, Utah. Cantrell is a management consultant to the Cosmos 1 program.

Simple Principle

Cosmos 1 has eight rotating, solar-sail "blades." Triangular in shape, the blades are about 50 feet (15 meters) long. They are made of aluminum-reinforced Mylar and are about a quarter the thickness of a trash bag. The spacecraft itself weighs only about 220 pounds (100 kilograms).

The principle of solar sailing is fairly simple: A spacecraft is pushed along by photons, or light "particles," emitted by the sun. The pressure of the photons as they bounce off the solar sails propels the craft, which theoretically doesn't need an engine.

In the case of Cosmos 1, scientists hope to fly the spacecraft for a few orbits around the Earth. Their goal is simply to demonstrate that the technology works.

"It's a modest goal—get it up there and fly a little bit under sunlight pressure and increase the orbit energy," Friedman said. "But I remind everybody that the Wright brothers only flew 12 seconds and went nowhere. But that flight was very important."

"Our goal is to do the same thing: to prove a technology that will later be used in many, many ways in much more elaborate developments," he added.

The solar sail spacecraft has another advantage over a chemical rocket: continuous acceleration. Sunlight striking the sails applies thrust continuously, enabling the sail (and spacecraft) to accelerate all the time.

In a hundred days a sail could top a speed of 10,000 miles an hour (16,000 kilometers an hour). In a year a sail could reach 36,000 miles an hour (58,000 kilometers an hour), and in three years it could top 100,000 miles an hour (160,000 kilometers an hour).

Giant Lasers

In theory solar sails could be used to boost or decrease the orbits of spacecraft. In a few decades, the scientists predict, sail-powered spacecraft may be used as interplanetary shuttles. Researchers add that one day the technology could even be used for interstellar flight.

One major problem is that once a theoretical solar-powered spacecraft gets much beyond the orbit of Jupiter, solar energy becomes too weak. Interstellar light sails would have to be powered by lasers.

"When sunlight grows too faint, powerful lasers could push your sail at even higher speeds," Friedman said. "The sail attached to your spaceship would be several kilometers wide, among the largest structures ever built, but as [thin] as spiderweb silk."

While that technology could be a century away, Friedman says he and his Cosmos 1 colleagues plan to aim a microwave beam on the spacecraft's sails to accelerate it.

"If we can actually measure the acceleration of a microwave beam on the spacecraft, that would be the first interstellar propulsion experiment," Friedman said.

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