Rocheworld (first published in serial form in 1982; first book publication, under the title The Flight of the Dragonfly, 1984) is a science fiction novel by Robert Forward which depicts a realistic interstellar mission using a laser driven light sail propulsion system to send the spaceship and a crew of 20 on a one-way journey of 5.9 light-years (ca. 34 trillion miles; ca. 56 trillion km) to explore a contact binary planet that orbits Barnard's Star, which they call Rocheworld, and where they make many startling discoveries. It had four sequels, written in collaboration with Julie Forward Fuller and Margaret Dodson Forward, which detail the exploration of the other worlds in the Barnard System: Return to Rocheworld, Marooned on Eden, Ocean Under the Ice, and Rescued from Paradise.
Plot A small group of civilian and military personnel carries out humanity's first crewed mission to another star system. They embark on a one-way exploratory mission to Barnard's Star, where planets have been discovered by a robot probe. They travel in a laser-driven light sail spacecraft christened Prometheus. The journey lasts 40 years, but the crew uses a drug called "No-Die," which slows their aging process, whilst lowering their effective I.Q. and emotional state to that of small children. They arrive only a decade physically older than when they left. They are cared for during this period by the ship's AI computer. At Barnard they begin their exploration, moving around the system and deploying various robot probes. Part of the crew then uses a lander to visit the contact binary planet Rocheworld, which consists of a solid-surface lobe they call Roche (French for rock as well as the name of the French mathematician who worked on Roche limits) and an ammonia/water-covered lobe they call Eau (French for water). A subset of the landing party journeys to Eau in the space-plane Dragonfly, which was carried on the lander. Over Eau the Dragonfly is caught in a violent storm that forces it to ditch. Unable to take off, the crew uses the plane's lift fans as propellers to make their way to the inner pole of the double planet, where the gravitation from Roche will help them to break free and return to the lander. While making this journey, the Dragonfly attracts the attention of one of the native species of the planet: the very intelligent but non-technological Flouwen. The Flouwen and the AI aboard the Dragonfly establish communications; the AI brings the Flouwen and the crew into contact and the two species begin to exchange cultural and scientific knowledge. The crew witnesses the birth of a Flouwen youngling, while one crew member takes a ride on a Flouwen who is fascinated by human technology. The Flouwen realize the humans are travelling to the pole and warn them that they are approaching a period where the configuration of the planetary system will cause the ocean on Eau to partially flow to Roche. They try to stop the humans from continuing into this violent event by pinning the spacecraft to the ocean floor with ice as ballast (water ice sinks in the ammonia-water solution of the ocean). The humans then realize that the interplanetary waterfall poses a threat to the lander crew remaining on Roche. Fortunately, the tidal stresses cause nearby dormant volcanoes to become active again. This melts an underwater glacier and floods the area with warm water, upon which the ice floats off the plane. The crew manages to get airborne and return to Roche. They rendezvous with the lander just as water is reaching it, and the entire landing party makes it back to the Prometheus. An epilogue is set many years later, when a follow-on mission arrives from Earth and is met by the sole surviving crew member, the others having died in accidents or from old age. This episode is expanded in the last sequel novel, Rescued from Paradise.
Forward's light sail propulsion system The light sail system consists of three functional parts: a powerful laser, a large focusing lens, and a giant space-sail. The idea behind the solar sail is that the laser provides a small force on the sail when the sail reflects the light. This small force provides the acceleration of the spaceship. With the ship's primary source of energy coming from the outside, it is not limited to traveling distances that it had enough fuel for. The light used in the system is from an array of a thousand laser generators, which are focused through lenses and aimed at the sail. The lasers provided up to 1,500 terawatts of power. Two different lenses were used to magnify the laser beams. The acceleration lens is 100 km in diameter and is able to accelerate the ship at 0.01g; the deceleration lens is 300 km in diameter and is able to decelerate the ship at 0.1g. Although these accelerations are relatively small, over time they result in enormous speeds. To catch the energy, Forward uses a 1,000-km-diameter circular aluminum sail. The sail resembles a flattened disk with a 300-km-diameter removable center portion. When traveling to Rocheworld, the entire sail is used. When the ship needs to decelerate, the smaller sail is separated from the larger outer sail. The large sail is used as a reflecting lens, focusing light onto the smaller sail, slowing the craft. Using the light sail system, the spaceship Prometheus accelerates for 20 years, traveling 2 light years' distance toward Barnard's Star before going into coast mode and traveling an additional 20 years' time at a constant speed of 0.2 c, covering the remaining 4 light years (ca. 23 trillion miles; 38 trillion km).
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