Going Interstellar (collection)

Until the 1970s, Kepler’s vision and Compton’s physics were good science but for space travel they were primarily an intellectual curiosity. With the anticipated return of Halley’s Comet in 1986, NASA commissioned a study of the feasibility of using a solar sail to rendezvous with the comet. The project never got off the ground, but it did get many space scientists and engineers thinking about solar sailing as something real, and the pace of sail technology development accelerated. The first big step was taken by Russia with the launch of their Znamya mirror in 1993. Znamya was a large, lightweight mirror flown in space to test the idea of using reflected sunlight to illuminate large areas on the ground at night. The mirror was made from very lightweight reflective materials and looked, for all practical purposes, like a solar sail.

In the late 1990s, the Europeans entered the picture with the ground-based development of a one hundred foot sail manufactured by the German company DLR (Deutschen Zentrums für Luft- und Raumfahrt). Though the sail never left the laboratory, it inspired NASA to develop a similar capability during the early 2000s that culminated in the testing of two different solar sails in the world’s largest vacuum chamber, which is located at the NASA Glenn Research Center’s Plumbrook Station. The two solar sails were one hundred feet in diameter, made from materials thinner than a human hair, and autonomously deployed under space vacuum conditions to test their space worthiness. Figure 5 shows the sail developed for NASA by L’Garde, Inc. just after a deployment test in the vacuum chamber.

Figure 5. NASA and L’Garde, Inc. tested a 100-foot diameter prototype solar sail in the mid-2000’s. Shown in the picture are the fully deployed solar sail and with four of the sail engineers standing in the foreground to show scale. (Image courtesy of NASA.)

Japan took the next major step in solar sailing by actually flying a sail in space and using it as a primary propulsion system. The IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) was launched in May 2010 on a trajectory that will take it on a voyage near Venus. Though smaller than the NASA and DLR ground demonstration sails, the sixty-five foot diameter sail showed the world that solar sails can be used in space for propulsion. Figure 6 shows the IKAROS in space after deployment.

Figure 6. The Japanese Aerospace Exploration Agency launched the IKAROS solar sail on a mission to Venus in 2010. Shown in the figure is an actual picture of the IKAROS sail after deployment taken by a small robotic camera ejected from the spacecraft during flight. (Image courtesy of the Japan Aerospace Exploration Agency.)

In 2010, NASA launched the NanoSail-D into low Earth orbit. NanoSail-D, (where D stands for drag) is not a functioning solar sail since it is not using the force of sunlight in a controlled manner for propulsion. The ten-square-foot NanoSail-D might instead be a space demonstration of more conventional windsailing. As NanoSail-D skimmed through the Earth’s uppermost atmosphere, the wind created by its passing caused the spacecraft to slow and eventually re-enter. The wind caused drag, giving NanoSail-D its name.

Other groups are planning small sail missions that will actually use sunlight pressure for propulsion. Chief among them is the Planetary Society’s LightSail-1. Similar in weight to NanoSail-D, LightSail-1 will have a sail three times larger and be capable of pointing toward the Sun in order to use the sunlight for propulsion. CU Aerospace and The University of Surrey have similar sails in development.

Following the successes of IKAROS and NanoSail-D, there has been renewed interest in solar sailing, and several countries are considering the development of even more ambitious sails for use in missions throughout the solar system. We have a long way to go, however, before we will have a sail that can be used to send a spacecraft beyond the edge of the solar system into the abyss between the stars.