Shiny and crinkly, the material looks more like something meant to wrap frozen foods than to provide a new way to travel through space. The aluminized Mylar reflects sunlight, thereby deriving a little kick from the recoiling photons. In principle, big sheets could act as solar sails that over time would reach speeds exceeding 100 kilometers a second¿far faster than chemical rockets.
The first solar sail, called Cosmos 1, will go for its test flight in early 2004. The demonstration of a revolutionary way to travel to the planets and maybe even to the stars would seem to be a natural activity for NASA, which spends several million dollars every year researching advanced propulsion systems. Yet in this case, the space agency has chosen to be a bystander.
The successful flight of Cosmos 1 would mark the culmination of three years of effort by the Planetary Society, a space-interest group, and the entertainment media firm Cosmos Studios [see "Sailing on Sunlight," News Scan, Scientific American, July 2001]. Both organizations, which can trace their roots to the late Carl Sagan, used their connections with Russian space officials and engineers. They enlisted the Babakin Space Center in Moscow as the prime contractor for Cosmos 1, which cost $4 million¿cheap in the space-travel world. The craft consists of eight triangular Mylar panels 14 meters long stretched across inflatable spars. The goal is to have Cosmos 1 ride atop a modified ballistic missile launched from a Russian submarine. Once in orbit, the spacecraft would inflate the spars to unfurl the sails. The panels would spread out like flower petals and cover about 600 square meters. Then sunlight should push the sails, lifting Cosmos 1 into a higher orbit from its initial 800-kilometer altitude.
Russian involvement may be one reason NASA has shied away, suggests Louis D. Friedman, executive director of the Planetary Society. Informal discussions had NASA supplying the sail material, which is tougher and, at 2.5 microns thick, half the thickness (and therefore half the weight) of the Russian film being used. "We would have gotten it for free and tested it for them," Friedman says. But NASA management never gave the go-ahead. Bureaucracy might have been a problem, he surmises, with the "upper echelons fearing private companies working with the Russians on a submarine launch." In any case, strict rules govern how closely NASA can work with other countries, remarks Hoppy Price, who was the lead solar-sail engineer for NASA at the Jet Propulsion Laboratory in Pasadena, Calif. "Possibly NASA is worried about the transfer of technology," he notes. Moreover, solar sails may provide some military advantage that the U.S. would rather not share. One proposed application, for instance, has solar sails hovering over the poles to provide valuable up-links to anyone at the earth¿s communications-starved extremities.
Risk, though, is probably the main reason for NASA¿s noninvolvement. Battered by a bruising report about the Columbia disaster as well as by the loss of two Mars-bound spacecraft in 1999, the agency "can¿t spend taxpayer money with the level of risk" that the Cosmos 1 team is taking, notes Neil Murphy, who currently coordinates the solar-sail work at JPL. Plenty of pitfalls abound. "Concern lies with what happens to an ultrathin material over tens of meters," Friedman says, noting that engineers have no good way on the earth to test the behavior of the material in zero gravity. "You can imagine all sorts of problems¿take Saran Wrap and wave it around," he offers. Ripping, fluttering and sagging would all undermine the sail¿s ability to reflect photons.
NASA would also want a solar-sail launch to have science-based goals to refine models and to plan the next mission, Murphy explains. Cosmos 1 is mostly a demonstration, and the components are not suitable for an extended voyage. The inflatable spars, for example, will not remain rigid for long because of the inevitable micrometeoroid impacts.
NASA is working on a more advanced solar-sail craft, probably to be configured as four square panels, but it won¿t be ready for at least another few years. That leaves the privately organized Cosmos 1 as the lone player¿and NASA engineers in the cheering section.