Solar sail development has surely been a frustrating thing for Sandy Montgomery, who knows that what stands in the way of pushing this technology into space isn't the need for scientific breakthroughs but adequate funding. Montgomery's team at Marshall Space Flight Center has been examining the potential of solar sails for a long time, and is well aware that leaving the propellant behind is a way to get more payload to your destination with considerably less overhead all around. And solar sails, which can ride the momentum imparted by photons from the Sun, are the ideal way to study 'propellantless' propulsion with near-term technologies. What a pleasure to see the launch window approaching for a solar sail deployment experiment in space, led by Montgomery's team and counterparts at NASA Ames. NanoSail-D is to be launched aboard a Space Exploration Technologies (SpaceX) Falcon rocket some time at the end of July or the beginning of August. Montgomery calls it the "...first fully...

Every now and then, someone writes to point out that when I write about the 'nearest star,' I am actually talking about the Sun. True enough, and despite our interstellar focus in these pages, I don't want to neglect the contribution of missions like SOHO, Ulysses, Hinode, STEREO and others to our understanding of how stars work. What we now need to deepen that knowledge further is a polar mission like POLARIS, which is being designed to make high-latitude studies of the Sun. For we have no extended studies of these regions, which will set up observations impossible to make from the ecliptic. Nor does the proposed Solar Orbiter mission offer a wide enough view of the polar regions. A new study of the POLARIS mission notes its purpose: to "determine the relation between the magnetism and dynamics of the Sun's polar regions and the solar cycle." Indeed, the spacecraft would map the solar magnetic field in 3-D as well as helping us understand its origins. But you knew there had to be...

A Finnish design making the news recently is hardly the only concept for near-term space sailing, but the possibility of testing it in space for a relatively small sum of money is attractive. This is especially true at a time when strapped budgets like NASA's are focused on ratcheting up conventional propulsion techniques to get us back to the Moon and on to Mars. Yes, let's keep pushing outward into nearby space with what we've got, but we need next-generation thinking, too, and the Finnish sail, the work of Pekka Janhunen and Arto Sandroos, points in that direction. Unlike magnetic sails that create an artificial magnetosphere around the spacecraft, the Finnish concept is to use long, thin conductive wires that are kept at a positive potential through the use of an onboard electron gun. The two researchers considered how the charged particles of the solar wind would interact with a single charged wire in a 2007 paper that we looked at in this Centauri Dreams article just over a...

Bear with me as I jump around wildly in this post, from Epsilon Eridani to happenings on our own Sun. The cause: Recent news about the solar wind from the Royal Astronomical Society's meeting in Belfast that has me thinking about magnetic sails. The concept seems made to order for in-system propulsion. Instead of catching the momentum of solar photons with a large physical sail, try riding the flow of charged particles coming out of the Sun by using a magnetic sail generated aboard the vehicle. Velocities of several hundred kilometers per second seem feasible. The thought of which reminded me to dig out a paper that Dana Andrews and Robert Zubrin presented at the 1990 Vision-21 symposium at NASA's Lewis Research Center (now Glenn Research Center) in Cleveland. Andrews and Zubrin had written several papers on the concept, noting one way a magsail could operate. From the Vision-21 proceedings: The magnetic sail, or Magsail, is a device which can be used to accelerate or decelerate a...

Some day we may be using solar sails to take payloads into an increasingly busy Solar System. Let's hope that day isn't far off, because the technology looks practical. But as we study solar sail methods, in which the sail is pushed by the momentum of photons, we also want to keep magnetic sail possibilities firmly in mind. A magsail could theoretically ride the 'solar wind,' that stream of charged particles pushing out from the Sun at speeds approaching 1.5 million kilometers per hour. Dana Andrews (Andrew Space) considered the problem of drag posed by interstellar ramjet concepts back in the 1980s, and along with fellow engineer Robert Zubrin went on to ponder how enormous magnetic sails could take advantage of the solar wind. The beauty of the concept is that you do away with a material structure of the sort so tricky to deploy in large solar sail designs. Instead, you generate the magsail from within the spacecraft. Couple this with a particle beam and you may have an...

Lou Friedman's work on solar sails dates back to his days at the Jet Propulsion Laboratory where, in the 1970s, his team began work on a rendezvous mission with Halley's Comet. It was a mission that never flew, but you can read about its planning stages in Friedman's book Starsailing: Solar Sails and Interstellar Travel (Wiley, 1988). That title is, as far as I know, the first book-length study of this technology, though it has since been joined by Colin McInnes' key text Solar Sailing: Technology, Dynamics and Mission Applications (Springer/Praxis, 1999). Now executive director of The Planetary Society, Friedman's interest in solar sails led to his work on the Society's Cosmos I mission, unfortunately lost during the launch attempt in 2005. His interest in interstellar issues remains keen as well, as evidenced by an article he recently wrote for Professional Pilot magazine. "Making Light Work" runs through solar sail basics for an audience that may seem surprising, but I can tell...

'Leave the propellant at home' is a key maxim of deep space exploration. If we can find ways to substantially reduce or even eliminate the need for on-board fuel tanks, we maximize the payload and enable missions that would otherwise be impossible. In the near term, solar sails are the ideal way to realize this goal. Driven by the momentum transfer of solar photons, sails can achieve high speeds and, by tacking methods that are in ways analogous to conventional ocean sailing, can move to and fro in the Solar System on their free photon ride. Laser and microwave beaming to sails is another thing entirely. We'll one day use those technologies for extended missions into the Kuiper Belt and the Oort Cloud and, if the dreams of some theorists come true, perhaps for interstellar missions at ten percent of light speed. But all that depends upon learning how sails work, and on that score, it's useful to know of the continuing NASA work on sail technologies. A recent paper by Les Johnson, Roy...

Someday fleets of interplanetary craft powered by the solar wind may cross the Solar System, using huge magnetic fields as their 'sails.' The concept is increasingly well understood, and I notice that researchers like Robert Winglee (University of Washington) have been extending it to include beamed propulsion methods as well (Winglee's concept is called MagBeam), useful if your goal is to move deeper still into nearby space. But for all this to happen, we'll need to learn much more about the solar wind itself and how we might ride it. Image: Artist's impression of a mini-magnetosphere deployed around a spacecraft. Plasma or ionized gas is trapped on the magnetic field lines generated onboard, and this plasma inflates the magnetic field much like hot air inflates a balloon. The mini-magnetosphere is then blown by the plasma wind from the Sun called the solar wind which has a speed of between about 350 to 800 km/s. Credit: Robert Winglee/University of Washington. Enter NASA's Solar...

The Royal Astronomical Society's recent meeting was laden with interesting papers, enough so that, with the added distraction of Gliese 581 c, I find myself still clearing out the backlog of newsworthy items. Otherwise, Centauri Dreams would have examined Ruth Bamford's work on radiation shielding much earlier. Bamford (Rutherford Appleton Laboratory) and team are working on a magnetic shield that would protect against dangerous cosmic rays and radiation. The work is significant because the radiation threat is real, and our current methods of dealing with it are inadequate for long-range space missions. Consider the International Space Station, where a chamber built for the purpose of radiation protection is available. The method works for the intermittent periods when solar radiation is intense (as from major flares), but such a chamber adds substantially to the mass of a spacecraft, becoming impractical on missions beyond Earth orbit. The new plan is to create an artificial...

We're at such an early stage in solar sail development that it will not be surprising if laboratory results lead us in entirely new directions. Consider James Benford's work at the Jet Propulsion Laboratory, where he and brother Gregory experimented with an ultralight 7.5 g/m2 carbon sail to test out microwave beam concepts. If the Planetary Society's Cosmos 1 sail mission had been successful, the Benfords would have been involved in a microwave experiment using the Deep Space Network's Goldstone antenna, a beamed propulsion test that a failed booster precluded. But the JPL work did lead to the interesting phenomenon of sublimation (also known as desorption). Put a microwave beam on the sail and you wind up with more acceleration than you expect. It's the result of the evaporation of absorbed molecules from the hot side of the sail. In a 2005 paper in Acta Astronautica that we reviewed in these pages, the Benfords looked at putting desorption to work by painting a sail with a...

It should come as no surprise that Eric Drexler has an interest in solar sails. Normally thought of for his contributions to nanotechnology, and especially his groundbreaking The Engines of Creation (Anchor, 1986), Drexler once discussed sail technologies in a short essay called "The Canvas of the Night." Sails present an obvious problem -- how do we stow such thin films for launch, then deploy them in space without damage. Wouldn't these issues be best resolved by building the sails in space? Drexler had this to say about the idea: Lightsails are what solar sails seem likely to become when we build them in space. They differ considerably from the deployable, plastic-film sails designed for launch by rocket from the ground. Not needing the toughness to survive folding, launch and deployment, lightsail reflectors need no plastic backing tens of thousands of atoms thick: they can be unbacked aluminum films just a few hundred atoms thick. Such thin foil cannot be made by smashing a bar...

A Finnish team has introduced a new wrinkle on the solar sail idea. Or more specifically, on the general principles of the magnetic sail, which would tap the propulsive power of the solar wind to push a 'sail' created as a field around the spacecraft itself. The so-called 'electric sail' would use fifty to one hundred 20-kilometer long charged tethers, their voltage maintained by a solar-powered electron gun aboard the vehicle. We're talking about tethers made of wires that are thinner than a human hair, thin enough that each can be wound into a small reel. But unwind the tethers and you get interesting results. The electric field of each wire now extends tens of meters into the solar wind flow. A single tether yields the equivalent effective area of a sail roughly a square kilometer in size. You can see the promise of deploying multiple tethers to reach high velocities. What's more, this sail allows the spacecraft to 'tack' towards the Sun as well as sailing outward from it. All...

If you're looking to shake out a solar sail design, a near-Earth asteroid (NEA) makes a tempting target. It's relatively close and offers the opportunity of a landing and sample return. That helps us work out the age, evolution and other characteristics of a class of objects that are potentially dangerous to our planet. It's no surprise, then, that when DLR, the German Aerospace Center, went into serious solar sail studies, it began to develop a dedicated mission via sail to one or more NEAs. That was in August of 2000, and it built on DLR's successful ground deployment of a square solar sail 20 meters to the side the previous December, conducted in a simulated weightless environment (see below). The DLR design is a square sail with four triangular sail segments, a valuable proof of concept in a time when little budgetary emphasis is being placed on sail designs by any of the major space agencies. Image: DLR's deployed solar sail, seen at the Center's facility in Cologne. Credit:...

Via advanced nanotechnology, the news that the Solid State Heat Capacity Laser (SSHCL) has achieved 67 kilowatts of average output power in the laboratory. Six to eight months of additional work are needed, it is believed, to reach the 100 kW mark. Which sets Brian Wang to pondering a "...proof of concept photonic laser propulsion system using mirrors to bounce laser light and multiply the effectiveness of lasers generate 35 micronewtons of thrust using low wattage lasers and 3000 bounces." Wang then quotes from a paper on multi-bounce methods by Geoffrey Landis and Robert A. Metzger. A major problem in laser lightsail techniques is reducing the power requirement, which can be onerous: It has been proposed that extremely small payloads (10 kg) could be delivered to Mars in only 10 days of travel time using laser-based lightsail craft (Meyer, 1984), but in order to do so, would require a 47 GW laser system. And if we start thinking interstellar, the laser numbers go sharply up. We're...

When we talk about solar sails for space missions, we normally think of physical objects, vast but incredibly thin sheets of high-tech material pushed by the momentum imparted by solar photons. Someday we may use such sails to ply routes between the planets, but as researchers ponder such technologies, they're also looking at the possibilities of magnetic sails using a different kind of propulsion. Rather than being pushed by photons, a magsail interacts with the plasma of the solar wind. And that makes for some interesting possibilities. The solar wind is a stream of charged particles moving at high speeds -- 500 kilometers per second and more -- and if you can harness it through technologies like Robert Winglee's Mini-Magnetospheric Plasma Propulsion (M2P2), you can ride that wind on a magnetic bubble hundreds of kilometers in diameter. Someday magsails may even provide deceleration capability for interstellar probes as they arrive in distant solar systems. All that puts the...

I don't want to move past Gregory and James Benford's interesting sail ideas without pausing to examine another paper that ran in the preceding issue of JBIS. It's a look at what we might do in the near-term with solar sails, written by Gregory Matloff (CUNY), Travis Taylor (BAE Systems) and collaborators. And it focuses on what inspired Centauri Dreams (the book) in the first place, the question of where we stand right now in terms of deep space propulsion. In other words, never mind the politics or the economics. If we had to launch a mission soon (obviously with a robotic rather than a human payload), how far could we go and how fast? Matloff and Taylor lay out the near-term possibilities for reaching the heliopause (roughly 200 AU) and the Sun's inner gravity focus (550 AU) using both sails and other propulsion options. The reference sail used here is a 100 meter disc massing some 157 kilograms, with structure and payload adding up to 100 kg for a total mass of 257 kg. Let me...

It's been some time since Centauri Dreams looked at the work Gregory Benford (University of California at Irvine) and his brother James (Microwave Sciences) are doing with solar sail concepts. But I just noted, in paging through a back issue of the Journal of the British Interplanetary Society, that their proposal for a microwave-beamed sail was written up there, based on a talk at the 2005 IAA symposium in Aosta, Italy. And because I want to keep sail concepts visible in a time when funding constraints have all but driven them from the news, let's revisit that work. What got the Benfords headlines not so long ago was the speeds they were proposing. Five years or less to Pluto? That's almost a halving of New Horizons' travel time, and it makes for some intriguing conjecture indeed. The Benfords learned from earlier laboratory experiments that heating up ultralight carbon sail materials causes accelerations greater than would be expected from the pressure of photons alone. Apparently...