Imagine, instead of the brute force of the rocket engine, a space propulsion system more like a sail: a vast expanse of gossamer-thin foil that would pull its payload from planet to planet utilizing the pressure of sunlight.
This concept, the solar sail, dates back to 1924. It was first suggested in the United States by engineer and science fiction writer Carl A. Wiley in a 1951 edition of Astounding Science Fiction. In 1975, the Jet Propulsion Laboratory (JPL) studied the solar sail intensively for the planned 1986 rendezvous with Halley's Comet, but dropped it for a more familiar propulsion system.
Despite the cancellation of the solar sail project four years ago, it caught the fancy of a number of aerospace engineers. Now the World space Foundation, a nonprofit organization dedicated to conducting space exploration and development , has announced its own solar sail project. It is expected to cost approximately $1 million -- "rather inexpensive for a space mission," says Robert L. Staehle, president of the foundation.
"We expect space enthusiasts to rally around the solar sail project as an opportunity to assure continued development of promising space technologies in the face of continued government cuts in civilian space budgets. For the price of a good magazine subscription people may support this project in return for periodic status bulletins, a piece of solar sail material, and other benefits, including the privilege of having their names carried aboard the solar sail on microfilm," Mr. Staehle explains.
That the $1 million can be raised from space enthusiasts seems reasonable. In similar fashion, $600,000 has been collected to support the continued operation of the Viking probes on Mars.
"We have about $100,000 in the treasury and are shortly expecting the donation of a solid fuel-rocket worth about $250,000," Staehle reports. To date , the foundation has been concentrating on getting private grants, such as $11, 000 which it received from the Lindbergh Foundation. It is in the very early stages of a promotional effort to get the backing of frustrated space exploration supporters.
As suggested by the relatively moderate price tag for the World Space Foundation's effort, the proposed solar sail is of modest proportions. It is 100 feet on a side and will carry a payload of 20 pounds. This is considerably smaller than the sail studied by JPL for the Halley's Comet mission. That was about a half-mile on a side and would have carried 500 pounds on a four- year course to intercept and parallel the famous comet's path toward the sun
However, if the first mission is a success, the Space Foundation would like to try one or two further missions which would involve sails 300 feet on a side.
"I think it's laudable that the World Space Foundation is trying to do this privately," says Dr. Louis Friedman, one of the JPL scientists involved in the solar sail project.They have good engineers involved, and I think they can make some positive contributions."
However, Dr. Friedman is not as optimistic as the foundation's leaders that the solar sail can be developed privately. "I think the solar sail will require a government program. I just hope that the foundation efforts will convince NASA [national Aeronautics and Space Administration] to pick it up again," he says.
Building a super-lightweight sail that can be packed tightly enough to be carred into orbit by the space shuttle, deployed successfully, and then controlled adequately for navigation in interplanetary space is not a simple task. "Nevertheless, all the technical challenges are pretty straightforward," says Friedman.
"This could be a very valuable small- scale test," Friedman believes. However, what he would really like is a number of these small sails to test over several years.
Still, the World Space Foundation project, should it succeed, could be a valuable first test of this intriguing concept.
(Further information may be obtained by writing: Secretary, World Space Foundation, Box Y, South Pasadena, Calif., 91030.)