Some years back at the Aosta interstellar conference I had the pleasure of being on a bus making its way at night through the Italian alps with Pekka Janhunen sitting immediately in front of me. Janhunen (Finnish Meteorological Institute) is the developer of the electric sail concept soon to be tested by the ESTCube-1 satellite, which launched last night aboard a Vega rocket from the Kourou spaceport in French Guiana. Our group had been talking about interstellar issues all day at the conference and now, headed back to the hotel following a memorable dinner at high elevation, I was curious whether an electric sail had interstellar applications. The immediate answer seemed to be no, given that the highest velocities Janhunen had been talking about for the idea were about 100 kilometers per second, much faster than Voyager 1's 17 kilometers per second, but a long way short of what we would like to see on an interstellar flight. But the ever thoughtful Pekka pointed out to me that as a...

It's always interesting how different strands of research can come together at unexpected moments. The last couple of posts on Centauri Dreams have involved new work on Titan, and early references in science fiction to Saturn's big moon. The science fiction treatments show the appeal of a distant object with an atmosphere, with writers speculating on its climate, its terrain, and the bizarre life-forms that might populate it. But early science fiction also proposed ways of reaching the outer Solar System, some of them echoed only decades later by scientists and engineers. Christopher Phoenix wrote in yesterday commenting on chemist and doughnut-mix master E. E. "Doc" Smith, who when he wasn't working for a midwestern milling company wrote space operas like The Skylark of Space on the side. Noting that Titan plays a major role in Smith's story Spacehounds of IPC, Phoenix pointed out that the tale may be the first appearance in science fiction of beamed propulsion. This was just weeks...

Hybrid propulsion technologies have emerged naturally as we look at ways to reach the stars. They're the result of trying to extract maximum performance from each option, and it sometimes turns out that putting two ideas together works better than either by itself. Next week we'll be looking at one such concept, A. A. Jackson's idea of combining the Bussard ramjet with laser beaming in ways that turn out to be surprisingly effective. Today I want to start the hybrid discussion - already about a week late because of competing news -- by talking about Johndale Solem's 'Medusa,' a combination of sail technologies with nuclear pulse propulsion. Solem's work evidently draws on the ideas of Ted Cotter at Los Alamos in the 1970s, which evolved into what George Dyson has described as a 'rotating-cable pusher.' Think back to the Orion concept, with its immense pusher-plate and shock absorbers that would withstand the explosion of nuclear devices behind the plate, propelling the vehicle...

Thinking about the poem "To Sail Beyond the Sun: A Luminous Collage," which I published excerpts from yesterday, I was reminded that if Ray Bradbury didn't spend a lot of time on solar sails, many of his compatriots did. Indeed, the early story of the solar sail is inseparable from science fiction. Astounding Science Fiction's John Campbell published the first serious look at solar sails for propulsion all the way back in May of 1951. The article's title, "Clipper Ships of Space," would be echoed by a highly influential paper by Gregory Matloff and Eugene Mallove called "Solar Sail Starships: The Clipper Ships of the Galaxy," which ran in the Journal of the British Interplanetary Society in 1981. The thirty years that passed between publication of the two articles saw the solar sail come into its own as a serious mission concept. Carl Wiley, who wrote the essay in Astounding, knew that many scientists and engineers were science fiction readers, but he was concerned enough about his...

I've been thinking about solar sails these past few days, a topic that inevitably invokes Arthur Holly Compton, who first demonstrated that x-rays have particle-like properties. Compton's experiments in 1923 produced a body of work for which he would receive the Nobel Prize in Physics later that decade. Thanks to him we learned that while photons have no mass, they do have momentum, a useful fact for space exploration in that momentum can be transferred to a thin reflective sail, like the Japanese IKAROS that was successfully launched and tested in space in 2010. No question that the force is tiny -- a sail would have to be a square mile in area to feel just five pounds of force at the Earth's distance from the Sun. The beauty of the sail, of course, is that it can keep producing thrust as long as it's in sunlight. But how to increase the thrust? In an essay in his new book Going Interstellar (edited with Jack McDevitt and just out from Baen), Les Johnson notes that if we wanted to...

Despite my best intentions, I still haven't put my hands on the exchange between Robert Forward and Ian Crawford on lightsails that ran back in 1986 in JBIS, nor have I managed to come up with the source of the 'lightsail on arrival' illustration I mentioned last week. This was the one showing a battered and torn sail docked in what I assume was a repair facility at the end of its long journey, and the effects of passage through the interstellar medium were all too obvious. It was a great image and I was frustrated about not being able to find the magazine it was published in, but an email from James Early quickly changed my mood. As opposed to the missing image that nagged at my memory, this was a case of having missed something perfectly obvious in the first place. I didn't know about the paper Jim did with Richard London on lightsails and the interstellar medium -- it was published in the Journal of Spacecraft and Rockets back in 2000, but somehow I didn't find it in the research...

You wouldn't think that slowing down a starship would be the subject of a totally engrossing novel, but that's the plot device in Poul Anderson's Tau Zero (1970, though based on a 1967 short story called "To Outlive Eternity"). Anderson's ramscoop starship, the Leonora Christine, can't slow down because of damage suffered in mid-cruise. Edging ever closer to the speed of light, the crew experiences all sorts of time dilation wonders as they wrestle to regain control, and the ending, while scientifically dubious, is also in every way unforgettable. Anderson could be guilty of over-writing but few writers are gifted with his sheer imaginative sweep. I'm thinking that coupling a ramscoop with a problem in deceleration is just the ticket for getting into the whole issue of starship arrivals. We can start with Robert Bussard's 1960 paper "Galactic Matter and Interstellar Spaceflight," which unwittingly paved the way for the whole magsail concept. Bussard came up with what for a time...

Minimizing the cost of a project is no small matter because, as Jim Benford points out in the paper we've been examining over the past several days, cost determines how we decide on competing claims for resources. In the case of a beamed sail mission and its infrastructure, the cost is largely the reusable launcher or 'beamer,' which is the beam source and the antennae needed to radiate the beam. Benford is able to derive general relations for cost-optimal transmitter aperture and beam power, from which he can estimate capital cost and operating cost using today's parameters. He can then study the economics of high-volume manufacturing. How to get from today's economics to tomorrow's? This is where the concept of the 'learning curve' comes into play -- it is the decrease in unit cost of hardware with increased production. A 90 percent learning curve means that the cost of a second item is 90 percent the cost of the first, while the fourth is 90 percent the cost of the second, and as...

There is a natural path through solar sails, which are now flying, toward beam-driven propulsion, and it's a path Jim Benford has been exploring for the last eighteen years. In my Centauri Dreams book I described how Jim and brother Gregory ran experiments demonstrating that carbon sails could be driven by microwave beams back in the year 2000. We learned that the theory worked -- a sail could indeed be propelled by a beam of photons -- and moreover, we learned that the configuration of the craft and propulsion system allowed it to be stable. Now we're talking about beam-riding, which the Benfords were able to demonstrate in later experiments. For it turns out that the pressure of the beam will keep a concave-shaped sail in tension, and as Jim pointed out in a recent email, the beam also produces a sideways restoring force. His work showed that a beam can also carry angular momentum and communicate it to the sail, allowing controllers to stabilize the structure against yaw and drift....

Back in August I mentioned NASA's solar sail plans beyond NanoSail-D in the context of a larger survey of sail designs and experimentation. It's great to see multiple sail projects in motion, and before I return to NASA I should mention not only the Planetary Society's ongoing sail effort but the CubeSat sail being built by a consortium from the University of Surrey and aerospace firm Astrium, an aerospace subsidiary of the European Aeronautic Defence and Space Company (EADS). Then there's the German space agency DLR and its Gossamer sails, experimental designs being worked on with the European Space Agency. Surely energized by the success of the Japanese IKAROS sail, work on this fledgeling space technology is beginning to ramp up. NASA's next step in sail design builds upon the earlier work the agency performed with aerospace contractor L'Garde Inc., of Tustin, California, which deployed and tested a 20m X 20m sail at the agency's Plumbrook facility in Ohio. The plan is to build a...

I see that the new agenda for the 100 Year Starship Study symposium has now been posted. The meeting will be held in Orlando in about a month, set up along a number of parallel tracks from interstellar destinations to propulsion options and habitats, a wide-ranging set of sessions that will allow many in the far-flung interstellar community to exchange ideas in person for the first time. DARPA's intention is to spur research and select an organization that will sustain and develop interstellar ideas over the next century, an exciting long-term prospect indeed. That interstellar flight demands long-term thinking should be obvious given the state of propulsion research today. Over the last sixty years, numerous ideas on how to drive a vehicle to a substantial percentage of the speed of light have been advanced, but almost all of these remain no more than concepts in journals. We're not remotely at the stage where we can choose a single option as the likely propulsion choice for...

Just how big does a spacecraft have to be to do productive work? It's a provocative question in this era of CubeSats and downsized budgets, but when you start thinking interstellar, there are even more reasons to wonder how small you can make your vehicle. After all, the propulsion challenges facing interstellar missions are profound, and the more mass (including, of course, the fuel you're carrying), the greater the problem. The rocket equation is telling, and one of the many things it tells us is that trying to reach a nearby star with a conventional rocket is out of the question, at least if you're hoping to get your mission there in a reasonable century or so. Mason Peck has been pondering issues like this for a long time. Those of you who are unfamiliar with his work at Cornell can catch up by reading earlier Centauri Dreams posts, but a more current solution is the article Exploring Space with Chip-sized Satellites, which runs in the current issue of IEEE Spectrum. In it, Peck...

We've often speculated about the potential uses of the solar wind in pushing a 'magsail' to high velocities for missions beyond the Solar System. This isn't solar sailing of the conventional type, in which the transfer of momentum from solar photons is the operating force. Instead of photons, a magsail would rely on the solar wind's stream of charged particles, which can reach speeds of up to 800 kilometers per second. One problem, of course, is that the solar wind varies hugely, variations that might make managing a magsail a daunting task. In any case, before we can contemplate such missions, we have much to learn about how the solar wind operates. Not all of that work is going to focus on our own Sun. We're also learning how stellar winds operate in other star systems through careful observation, as new work from the European Space Agency's XMM-Newton space observatory reminds us. The spacecraft recently observed a flare during a scheduled 12.5-hour observation of a system known...

Spacecraft no more than an inch square will fly aboard the next (and last) Shuttle flight to the International Space Station. The work of Mason Peck (Cornell University), the micro-satellites weigh in at less than one ten-millionth of the mass of the original Sputnik, yet can accomodate all the systems we associate with a spacecraft -- power, propulsion, communications -- on a single microchip. We've looked at Peck's work in previous Centauri Dreams essays (see this one on 'smart dust'), but it's great to see some of his concepts put into an actual mission plan for testing in Earth orbit. What Peck has in mind with the spacecraft he calls 'Sprite' is ultimately to create a satellite with different flight dynamics from other spacecraft. Sure, we can miniaturize our electronics and create satellites with small form factors -- CubeSats come to mind -- but Peck's craft call up a different analogy: "Their small size allows them to travel like space dust," said Peck. "Blown by solar winds,...

Remember Arthur C. Clarke's "The Wind from the Sun"? The short story, telling of a race from the Earth to the Moon via solar sail, appeared in 1964, portraying the vessel Diana and its 50 million square foot sail, all linked to its command capsule by a hundred miles of cable. In those days, the sail idea was newly minted and more or less the domain of science fiction buffs, who had first encountered it in Carl Wiley's "Clipper Ships of Space," a non-fiction article written under a nom de plume for Astounding Science Fiction in 1951. The 1960s would see tales like Poul Anderson's "Sunjammer" and Cordwainer Smith's haunting "The Lady Who Sailed the Soul." Addendum: When I say the idea was 'newly minted' (above), I'm referring to the engineering ideas that could go into an actual mission. The idea of solar sailing itself goes back much further -- see my Centauri Dreams book for the whole backstory. Wiley's sail concept was startlingly ambitious for its time, an 80-kilometer design that...

Good fortune continues to smile on Japan's IKAROS solar sail. First of all, we can point to the image at left, a small shot to be sure but an amazing one nonetheless. Emily Lakdawalla explains on the Planetary Society's blog that IKAROS' transmitter is not powerful, so that it took a full two weeks to transmit the image from the spacecraft to Earth, and at that, it's just a thumbnail. But take a look -- what you see is the sail itself and, in the background, Venus. Think about it: A solar sail has successfully made an interplanetary crossing. Yesterday the JAXA controllers behind the IKAROS mission confirmed that its first six months of life have been all but flawless, and the mission has been extended to March of 2012. This includes the deployment of its 20-meter diagonal, 0.0075 milimeter thick polyimide sail -- you may remember that was a bit of a nail-biter from here because I was trying to translate tweets in Japanese and follow the incoming imagery, which at one point seemed to...

Suppose we have developed an Earth-Moon industrial system, one that lets us use an electric launch system on the Moon to upload mass for chemical processing and the extraction of raw materials. What's the next step toward extending it to the entire system? One idea, as Joseph Friedlander has been explaining on the NextBigFuture blog, is to do interesting things at the L4-L5 points, where stable gravitational pockets exist. Friedlander is thinking about building solar sails in space, and in this regard he echoes nanotechnology maven Eric Drexler, who wrote about sail technologies in The Engines of Creation (1986). Here's Drexler on the subject: To build lightsails with bulk technology, we must learn to make them in space; their vast reflectors will be too delicate to survive launch and unfolding. We will need to construct scaffolding structures, manufacture thin-film reflectors, and use remotely controlled robot arms in space. But space planners already aim to master construction,...

A phone call from NASA's Kim Newton at Marshall Space Flight Center confirms what some of us were beginning to fear, that the ejection sequence that would separate NanoSail-D from FASTSAT, at first thought successful, has apparently malfunctioned. Although telemetry from FASTSAT looked good and seemed to confirm the ejection, the NanoSail-D team has no beacon from the sail, and while attempts to locate it will continue throughout the weekend, the outlook has suddenly turned grim.

While we wait for the NanoSail-D deployment, let's talk about how to control a space-based solar sail. Japan's IKAROS sail uses liquid crystal devices along the outer edge of the sail that actually allow the ground team to adjust the reflectivity of portions of the sail. Do that and you've created a situation where one part of the sail gets more of a boost from incoming photons than another, making it possible to maneuver the sail by light alone. It's ingenious technology and, at least in early tests, seems to work. Getting a sail to function seems easy. The tricky part is controlling what it does. We know that photons have no mass, but they do impart momentum, so that putting any large, reflective surface into space should result in forces acting upon it. James Clerk Maxwell demonstrated the basic principle as far back as 1873, although Johannes Kepler, observing the behavior of cometary tails, assumed they were affected by a 'solar wind' that could eventually be used to move a...