In June 2005, if all goes well, a new type of spacecraft will be launched into Earth’s orbit. In a manner echoing back to the age of adventure and discovery on the high seas, this new vessel, called Cosmos 1, will unfurl gossamer-thin sails to catch the sun’s rays on a voyage across the solar system. It will also catch the attention of science fiction aficionados everywhere, as it has taken over eighty years for the technology to make the journey from imagination into reality.
A solar sail is a deceptively simple idea—a thin sheet of metallic material with a large mirrored surface area is positioned to reflect photons, or particles of light. As the photons rebound off the sail, they exert a tiny but constant pressure on it, known as “light pressure.” As there is theoretically no opposing force, such as friction, the sail should experience a continuous acceleration that will last as long as it faces the sun.
The Russian space pioneer Konstantin Tsiolkovsky, famous for his influence on the Soviet rocket program, is credited with first developing the concept back in the early 1920s, but it wasn’t until the exciting boom years of the space race in the 1950s that the solar sail came to widespread attention. In an article written for the May 1951 edition of the magazine Astounding Science Fiction, Carl Wiley described how a craft could be finely controlled using a light sail. However, due to his concerns about how the wider space research community would react to his ideas, Carl wrote the piece under the pseudonym Russell Saunders.
The romance of using a solar sail to cruise silently across the solar system, or indeed beyond it, was not lost on science fiction writers. The appeal of a technology that credibly offers the possibility of opening up space for exploration is not hard to understand—the science the idea is based on does not require the suspension of disbelief in the readers; no unexplained “worm holes” or “hyper drives” need to be invented to push the narrative along, while the elegant simplicity of the concept suggested that solar ships could be just around the corner. In the next decade the idea blossomed within the fertile imaginations of such heavyweights of the genre as Arthur C Clarke, who developed the idea with a story, “The Wind from the Sun,” published in 1964. The plot revolved around a regatta in which seven “sun yachts” compete in a literal space race to get from the Earth to the Moon, which allowed the author to develop his ideas for a number of possible designs. While other writers had produced solar sail-inspired stories before him, the credit for the first story going to Cordwainer Smith with “The Lady who Sailed The Soul” in 1960, it is often Clarke’s story that current researchers in the field credit with sparking their interest in this area of space research.
The concept, in theory at least, has proved to be very attractive for space researchers as the need for the craft to carry fuel for propulsion is eliminated, increasing its capacity to carry instruments and allowing more ambitious missions than are currently possible. The possibility of continuous acceleration allows for much faster velocities than can be achieved with conventional rocket propulsion, vastly reducing the time taken to travel across the solar system. In addition, rather than having to use precious fuel to change the vessel’s position when approaching a planet’s orbit, the craft would be able to use its sails to brake and maneuver. Indeed, some have described it as the only practical technology within our reach for humankind to use to explore the stars.
However simple the idea may appear to be, it has taken a long time for it to move out of the realm of fiction. Early studies into the technology during the 1960s by NASA were abandoned after the success of the Apollo missions led to public ennui for space research and funding waned. In the late 1970s Lou Friedman, one of the engineers behind the current Cosmos 1 venture, led a project at NASA’s Jet Propulsion Laboratory (JPL) to investigate the feasibility of using an enormous solar sail to rendezvous with Halley’s Comet. While the researchers were confident about their plan and had arrived at a practical design, the conservative management at NASA balked at the untried technology as well as the short timescale required to launch the craft in order to reach the comet on schedule. Friedman now acknowledges in “The History of Solar Sailing” that the timescale was much too short, especially as their estimates relied on NASA's space abilities improving at a faster rate than proved to be the case.
The Planetary Society—a privately funded US organization founded in 1980 by Friedman, the popular scientist and writer Carl Sagan, and Bruce Murray, the former director of the JPL—is behind the Cosmos 1 project, which will be the first experiment aimed at testing the viability of using a solar sail to propel a craft in space. Appropriately enough, considering the origins of the concept with Konstantin, the project has been developed in cooperation with Russia. While the Planetary Society has gathered the comparatively meager budget of US$4 million (€2.1 million) and coordinated the project, the sail itself has been built in Moscow by NPO Lavochkin (NPO is a Russian acronym meaning Research/Production Association) and will be launched from a Russian nuclear submarine in the Barents Sea. Russian cooperation has also given the team access to technology vital to the solar sail’s success, as NPO Lavochkin was already involved in developing inflatable equipment for use in space—an element integral to the design of the solar sail as its masts inflate in space. The Cosmos 1 sail has a design akin to that of a windmill with eight blades that can be configured in different positions to allow directional control, in theory enabling the craft to tack in much the same way that a traditional sailing ship would.
The Cosmos 1 team is not the only group making progress in this area of space research. The Japanese Institute of Space Astronautical Science (ISAS) stole the march on them somewhat last year by being the first to successfully manage the complex task of unfurling a thin metallic sail in space. ISAS launched a rocket last August carrying a payload of two solar sails, enabling them to test the unraveling of two different configurations. The first design, a circular sail made of four segments, was deployed at 150 km, while the second design, a slightly more complex shape made of six segments, was deployed at 170 km after the first sail was released. The institute has made many important strides forward in space propulsion research, especially with ion drives, another cutting-edge propulsion technology. Their eventual aim is an ambitious craft powered by a hybrid of the two systems.
The Planetary Society’s project, though, is the closest to getting a solar sail into orbit to test the principles of the concept itself. In the days after being put into orbit, the craft will be put through its paces, the sails being slowly deployed in two careful stages, before being used in an attempt to raise the orbit of the craft using light pressure from the sun. A number of challenges will need to be faced along the way, as no one is sure how its structure will cope with the buffeting it will be exposed to along the way. A successful Cosmos 1 test is likely to spur other organizations into bringing their designs out of the planning stages. NASA and the European Space Agency (ESA) both have plans to use solar sail-powered probes to study the sun from a closer vantage. There are also more futuristic ideas to try boosting the initial acceleration of a solar sail by using a powerful laser to push it.
Cosmos 1’s mylar sail is expected to degrade within a month or so in the direct sunlight, and without it the craft itself will eventually burn up in Earth’s atmosphere. Many will be hoping that its death pyre will signal the beginning of the solar sail’s journey from fiction into reality.