Rudolph Meyer's work on solar arrays and ion propulsion elicited quite a few e-mails asking for further information. I don't yet have the Acta Astronautica paper that spells out the details -- nor do I know just how detailed Meyer gets -- but I'll try to provide some answers soon. In the interim, I was startled to realize that Geoffrey Landis, who commented on the Meyer design for New Scientist, had actually gone into this concept at some length as long ago as 1989. In fact, Landis' key paper "Optics and Materials Considerations for a Laser-propelled Lightsail" (available here) was presented at the 40th International Astronautical Federation Congress in that year. Landis speculated on a lightweight sail that focuses power on a small solar array, noting that a basic problem with laser-propelled lightsails is their low energy efficiency: The energy efficiency may be greatly improved, at the cost of a reduction in specific impulse, by combining the laser sail with a photovoltaic powered...

Most papers about interstellar flight appear in serious venues like Acta Astronautica or the Journal of the British Interplanetary Society. The latter, in fact, has emerged as the leading arena for such discussions, and the growth of the arXiv site has brought many new ideas to light in the digital realm. It may be surprising, then, to find that the popular Astounding Science Fiction was once a key player in interstellar theory with the publication of an article that brought solar sails to the attention of the public -- and to many scientists -- for the first time. But the magazine, in the hands of the capable John Campbell, was often home to science essays, and none more prescient than this one. "Clipper Ships of Space" appeared under the byline Russell Saunders in Astounding's issue of May, 1951. 'Saunders' was in reality an engineer named Carl Wiley, who we may speculate wrote under a pseudonym to avoid any damage to his reputation -- many scientists and engineers read science...

We need to learn everything we can about the solar wind. A stream of charged particles moving at 500 kilometers per second and more, it may one day provide the push for fast missions to the outer Solar System and beyond. Magnetic sail concepts like Robert Winglee's Mini-Magnetospheric Plasma Propulsion (M2P2) would operate by injecting plasma into a magnetic field to create the sail, which is actually a huge magnetic bubble. And because such a sail is not a physical structure, sail diameters of hundreds of kilometers are possible. Riding the solar wind, a sail like this would sharply reduce travel time to Jupiter and beyond, and it's possible to imagine future versions pushed not by the solar wind but particle beams -- now we're talking interstellar. Take the concept a step farther and you've produced, as physicists Dana Andrews and Robert Zubrin first deduced, an ideal method of braking upon arrival into a destination solar system. After the long cruise, an interstellar spacecraft...

A solar sail competition to drive research? It's a great idea, and one that has been explored in the past. Indeed, a whole variety of groups have looked into the possibility, from France's Union pour la Promotion de la Propulsion Photonique (U3P) to Russia's Space Regatta Consortium and the Aero-Club de France. And official rules for the Luna Cup were approved by the International Astronautical Federation at the World Space Congress in August of 1992, outlining a solar sail race to the Moon. Now I'm looking at a NASA announcement passed along by James Benford that outlines prize competitions to be conducted under the agency's Centennial Challenges umbrella. To quote from the document, "By making awards based on actual achievements instead of proposals, Centennial Challenges seeks novel and lower-cost solutions to engineering obstacles in civil space and aeronautics from new sources of innovation in industry, academia, and the public." The challenge possibilities are outlined in a...

Solar sails are ideal for long missions within the Solar System, but their manifest advantages (no fuel onboard!) are not unalloyed. A major issue is the time needed to escape Earth orbit. Working the numbers on this, Gregory Benford noted that if a sail used the momentum from solar photons alone, unassisted by any other propulsive force, it would require time scales on the order of years to escape from Earth's gravity. And that's with sail deployment from an altitude of 800 kilometers, beyond the reach of decelerating air drag. What we can do to get that sail on its way faster is the subject of Benford's new paper in Acta Astronautica, written in collaboration with Paul Nissenson. One possibility is to coat the sail with a material that sublimes; when heated, the material vaporizes and is ejected, adding to the momentum transfer of photons (Benford and his brother James at Microwave Sciences have done groundbreaking work on the nature of such sublimation, also called desorption)....

If we chose to launch an interstellar probe using near-term technologies, it would almost surely be a solar sail, unfurled on a close approach to the Sun and flung outward at speeds that could get it to Alpha Centauri in perhaps 1000 years. That's the thinking of Gregory Matloff, author of Deep Space Probes: To the Outer Solar System and Beyond (Springer, 2005) and a leading proponent of interstellar studies. Later technologies might also use sails, driven by laser or microwave or even particle beams. But as we take incremental steps toward an interstellar future, solar sails have to be developed first. On that score, it's interesting to note the contributions of the Deutschen Zentrum für Luft- und Raumfahrt (DLR), Germany's aerospace research center and space agency. An early consolidation of sail studies, for example, came from a joint NASA/DLR feasibility study conducted in 1996-97. The working group recommended a demonstration mission that could help develop the basic principles...

The theories behind solar sailing go back a long way -- some would trace them to the days of Kepler. But papers on actual mission design began to emerge only in the 1950s, when 'Russell Saunders' (the pseudonym of aeronautical engineer Carl Wiley) wrote a sail description for a 1951 issue of John Campbell's Astounding Science Fiction. That paper was followed by Richard Garwin's more technical analysis in a 1958 issue of the journal Jet Propulsion. Now another paper from that era has surfaced and is available online. T.P. Cotter's "An Encomium on Solar Sailing" was produced in 1958 as an informal report for Los Alamos (originally no more than an office memorandum), and was issued in more comprehensive form in 1973. Cotter described his intent as not to break new ground but to fill in the details of the solar sail idea through an actual design, an unmanned sail mission to Mars. The Cotter sail is a flat, circular disk some 10-4 cm thick and 500 meters in diameter. It is made of a...

James Benford's JPL experiments pushing an ultralight carbon sail with a microwave beam were the first solid demonstration that the beamed sail concept would work. Both James and brother Gregory were deeply involved in the design of the Cosmos 1 solar sail mission, and understandably disappointed that its microwave experiment -- aimed at demonstrating a microwave push on the orbiting craft from the Deep Space Network's Goldstone antenna on Earth -- was never completed. But an interesting offshoot of the JPL study was that while photon pressure on the sail was clearly demonstrated, the power of the beam did not account for all the observed acceleration. Something else was clearly at work, evidently the evaporation of absorbed molecules from the hot side of the sail, a phenomenon known as desorption. In a March, 2005 paper for Acta Astronautica, the Benford brothers suggest using this effect to achieve additional thrust over conventional solar sail designs. In fact, a microwave sail...

Regular readers of Centauri Dreams will know James Benford as the scientist who showed that microwaves could move a sail in a vacuum. That experiment, performed at the Jet Propulsion Laboratory, involved a 10-kilowatt microwave beam and a 10 sq cm sail in a vacuum chamber. The material used was a carbon fiber material commonly called carbon-carbon, in which carbon molecules are fused together in a structure called a 'microtruss.' Developed by San Diego's Energy Science Research Laboratories, carbon-carbon is terrifically interesting as a possible material for early solar and beamed sail work. The president of Microwave Sciences in Lafayette CA, Benford wrote in a recent e-mail about the failed Cosmos 1 solar sail launch. He had hoped to oversee a microwave experiment using the Deep Space Network's Goldstone facilities to test the effects of a microwave beam on a sail in operational conditions, but that was not to be. At least, not this time. Benford's message is worth quoting, and is...

This statement was released by The Planetary Society at 13:30 EDT: "In the past twenty-four hours, the Russian space agency (RKA) has made a tentative conclusion that the Volna rocket carrying Cosmos 1 failed during the firing of the first stage. This would mean that Cosmos 1 is lost. While it is likely that this conclusion is correct, there are some inconsistent indications from information received from other sources. The Cosmos 1 team observed what appear to be signals, that looks like they are from the spacecraft when it was over the first three ground stations and some Doppler data over one of these stations. This might indicate that Cosmos 1 made it into orbit, but probably a lower one than intended. "The project team now considers this to be a very small probability. But because there is a slim chance that it might be so, efforts to contact and track the spacecraft continue. We are working with US Strategic Command to provide additional information in a day or so. "If the...

The Planetary Society's servers were slammed yesterday through the launch and aftermath of the Cosmos 1 mission, but the entries again available on Emily Lakdawalla's more or less official weblog make for grim reading this morning. For that matter, so does the silence that follows her post at 1915 EDT last night, saying that the search continued for Cosmos 1, but the ground stations that expected to receive the spacecraft's signal have come up empty. True, some signals have been detected, but are they the right ones? Project director Louis Friedman puts it this way: "That the weak signals were recorded at the expected times of spacecraft passes over the ground stations is encouraging, but in no way are they conclusive enough for us to be sure that they came from Cosmos 1 working in orbit." The Russian space agency indicated that the Volna rocket may have had a problem during its first or second stage firing. "This," Friedman noted, "would almost certainly have prevented the...

We're a little over a day from the Cosmos 1 solar sail launch, testing the technologies that may one day make travel within the inner Solar System faster and far more efficient. Centauri Dreams has discussed the involvement of Ann Druyan's Cosmos Studios; the documentary film and entertainment company put $4 million into the project, which is led by The Planetary Society. But it's also important to acknowledge the major Russian contribution, and not just in the Volna rocket that will launch the satellite, or the Russian submarine from which it will be fired. No, the Russian involvement is deeper still: the space firm NPO Lavochkin is behind much of the design of Cosmos 1, and the Russian Academy of Science's Space Research Institute is a major player. All told, Cosmos 1 is a case of trans-national collaboration, a fact emphasized by the scattering of team members around the globe as the launch approaches. The Planetary Society's Viktor Kerzhanovich is now in the Marshall Islands,...

As we near launch, let's run through the Cosmos 1 sail mission again. The vehicle is privately funded (by Ann Druyan's Cosmos Studios and The Planetary Society), and will be launched aboard a converted Russian ICBM. Once in orbit, the spacecraft will deploy eight mylar sails. The principle is straightforward: Photons have no mass but they do carry momentum. As solar photons strike the sail blades, Cosmos 1's orbit should change, providing a test of solar sailing that can be measured from the ground. A later microwave beaming experiment may be able to measure the effect beamed propulsion has on the spacecraft, though the primary mission goal remains to test the principles of solar sailing by photons alone. Launch is now scheduled for June 21 from a submerged Russian submarine in the Barents Sea. The mission will be controlled from the Lavochkin Association in Moscow and assisted by a project operations center at The Planetary Society's headquarters in Pasadena. Everyone will be...