When engineer Carl Wiley brought solar sails to a wide audience in 1951, he envisioned a particular kind of sail. Wiley, who wrote under the byline Russell Saunders, published "Clipper Ships of Space" in the May issue of Astounding Science Fiction that year, seven years before the first technical paper on sails, Richard Garwin's "Solar Sailing: A Practical Method of Propulsion within the Solar System," appeared in the journal Jet Propulsion. As you can see in the illustration, which ran with the original essay in Astounding, Wiley envisioned the sail as taking a parachute shape, with the payload attached to the sail circumference. Varieties of Sail Design But there are many ways of doing sails. Square or rectangular sail designs (think of those images of IKAROS shot by its detached cameras) have been the focus of recent work, with the result that many alternatives have not reached the same level of technological readiness. But along with parachute sails, spinning disk sails,...

Japan's IKAROS sail has thus far conducted a triumphant mission, demonstrating the principles of sail deployment, solar photon propulsion and attitude control in a functioning space sail. While the solar sail community has never received the press attention I believe this innovative propulsion technology deserves, it's heartening to realize that a long and sustained effort, even one operating under the radar, so to speak, can produce such striking results. The 2nd International Symposium on Solar Sailing (ISSS 2010) has just wrapped up in Brooklyn, but if you go back to the first of these conferences, conducted in June of 2007 in Ammersee, Germany, you'll find that the program was laced with representatives of ESA, NASA and JAXA (presentations from that meeting are available online), attacking the issue of getting a solar sail operational from every angle even as the budgets of the representative agencies were being cut back. The needed theoretical work proceeds absent the necessary...

Robert Forward's Indistinguishable from Magic is a genial and absorbing read, a collection of essays and fiction illustrating some of the scientist's most memorable ideas. And while gigantic lightsails driven by laser beam to other stars always come to mind when Forward's name is mentioned, it's fascinating to page through his thoughts on antimatter, black holes and time machines. Long a Forward admirer, I was pleased to see that another of the concepts discussed in this book recently made an appearance at this month's solar sail conference in Brooklyn. 'Statites' are a Forward construct, a word he coined to describe a spacecraft that uses a solar sail to hover over a region rather than orbiting the Earth. Let Forward describe what he calls a 'technique for hanging things in the sky': ...I have the patent on it -- U.S. Patent 5,183,225 "Statite: Spacecraft That Utilizes Light Pressure and Method of Use"... The unique concept described in the patent is to attach a television broadcast...

With more attention now being focused on possible missions to an asteroid, we should keep in mind that DLR, the German Aerospace Center, has been looking into an asteroid mission via solar sail for some time now. One 2006 paper from DLR's Institute of Space Simulation pondered a 70-meter sail for use in a projected mission to the Near-Earth Object 1996FG3 within ten years of launch. It's an interesting notion, one that would involve the sail hovering over the NEA hemisphere opposite to the Sun, deploying a lander and return capsule. DLR has been into serious sail studies for some time now, as the photo below attests. It's a 1999 shot of the ground deployment of a square solar sail 20 meters to the side. As you can see, this is a square sail made up of four triangular sail segments, an exercise that could readily lead to a sail deployment in space if the European Space Agency opts for funding such a mission. Just what ESA has in mind for such technology was the subject of a...

The final day of the Second International Symposium on Solar Sailing (ISSS 2010) kicks off this morning with Roman Kezerashvili (City University of New York) discussing solar sail missions as a way of testing fundamental physics. Last year in Aosta I listened with fascination as Kezerashvili discussed close solar passes ('Sundiver' missions) that could approach as close as 0.05 to 0.1 AU to the Sun, depending on the development of materials technology. The remarkable feature of his talk, though, was the consideration of General Relativity's effects in such close proximity to the Sun, which could create huge navigation issues. The 'Sundiver' as an Exercise in Physics Fail to account precisely for spacetime curvature and frame dragging in this environment and such a mission could find itself with a million-kilometer deflection enroute to its target. Even more exotically, time slows in close proximity to the Sun due to relativistic effects, so that the observer on Earth measures about...

Solar Sails in Brooklyn I should probably clean out my office, and would, if I could find the time, but things keep happening in the deep space community and I keep writing about them. I had the program for ISSS 2010 (the Second International Symposium on Solar Sailing) right beside me when I started to write yesterday's entry, and by the time I got to the part on the conference, the program had disappeared into the wilderness of printouts, notebooks and letters. Thus I missed the fact that Colin McInnes would be in attendance at the sessions, a major addition to the already stellar lineup. McInnes could be said to have written 'the' book on solar sailing, a densely packed tome that lays out the principles and speculates on future missions. Meanwhile, it's heartening to see how international the solar sail effort has been from the outset, even if all the space agencies have continued to wrestle with their own funding demons. Much good work has gone on at Germany's DLR, for example,...