My friend Tibor Pacher has taken our interstellar bet to a new level, publishing a lengthy letter on the subject in the current Spaceflight, a journal published by the British Interplanetary Society. Tibor, remember, had made a prediction I found outlandish: That "the first true interstellar mission, targeted at the closest star to the Sun or even farther, will be launched before or on 6 December 2025, and will be widely supported by the public." I dissented, and we went public with the bet on the Long Bets site. Our funds are in the hands of the Long Now Foundation, with all proceeds going to good causes (details on the site). But while I have enjoyed tweaking Tibor about the bet, it must be said that he has a solid motivation for going so far out on the speculative limb. The visionary founder of peregrinus interstellar, Tibor hopes to provoke discussion and keep people thinking. Along those lines, then, let's look at his recent letter. One of the mission specs was a flight time of...

By Larry Klaes Tau Zero journalist Larry Klaes takes on an old subject with a new twist: The multi-generational starship. It's a familiar trope in science fiction (think Brian Aldiss' Non-Stop or Heinlein's 'Universe'), but one given modern impetus in the hands of a small team of visionaries dedicated to making it happen. These guys think big, not just in terms of ship size but trip duration (ten thousand years!), and envision at least 500 years as the time needed to get their project ready to launch. Always a promoter of long-term thinking, Centauri Dreams follows the improbable tale with considerable interest. Despite how they appear to us in the night sky and the relative ease and speed with which spaceships in most science fiction stories fly to them, the twinkling stars in the heavens are, in reality, immensely far away. The few robotic probes that have left our Solar System faster than any other vehicles yet built would not -- if aimed in their direction -- reach the the...

From the first anniversary edition of the Carnival of Space, I'll send you this week to Brian Wang's discussion of two propulsion concepts for the near future. VASIMR (variable specific impulse magnetoplasma rocket) is under active development at Franklin Chang Diaz' Ad Astra Rocket Company, a site to monitor for developments in a technology that offers potential specific impulses from 1,000 to 30,000 seconds. That's a major upgrade compared to conventional rocket designs, and one that could conceivably get us to Mars in as little as 39 days. The Finnish solar electric sail concept, which we've also looked at here, may be well enough along for a flight test in 2010, assuming the budgetary gods are smiling. Our next step outward depends upon bumping up trip times to relatively nearby destinations like Mars and the asteroids, and these are two of the more promising concepts for making that a reality.

When you're thinking interstellar, long time frames are inescapable. Are we capable as a culture of planning missions that last not only longer than a single human lifetime, but longer than multiple generations? Steve Kilston (Ball Aerospace & Technologies), with help from Sven and Nancy Grenander, clearly thinks so. The three are behind the fittingly named Ultimate Project, a starship designed to carry one million humans across the light years separating us from the nearest stars, creating colonies and perhaps going on from there, a ten thousand year star journey that could turn into a trek through the galaxy lasting for millions more. For just to get such a mission to the launch point, Kilston is thinking in terms of century-long segments within an overall 500-year plan. 100 years to develop the plan for the mission. 100 more years to achieve a detailed design. Now a century for prototyping and demonstrating technologies, followed by a century to assemble materials and construct...

Project Daedalus, discussed frequently in these pages, was the first in-depth design study of an interstellar probe. Its projected fifty-year flyby mission to Barnard's Star at 12 percent of the speed of light was beyond contemporary technology (and certainly engineering!), but not so far beyond as to render the design purely an intellectual exercise. I bring up Daedalus again because I keep getting asked about Project Longshot, which some have mistakenly seen as a successor to Daedalus with a NASA pedigree. And wasn't Longshot a far more advanced design? Actually, no. But the other day I again ran into Longshot in the form of an online post describing it as a hundred-year mission to Alpha Centauri (true enough), evidence that NASA had the technology right now (not true) to get us to the nearest stellar system in a century, which would be faster by far than the thousand years I've always used as an absolute minimum for getting there with the technology we have today. Even that 1000...

Centauri Dreams' rarely spends time close to the Sun, preferring to focus on stars other than our own, and their planets. But the MESSENGER spacecraft's close pass by Mercury, leading eventually to orbit, does have an interstellar connection in the person of project scientist Ralph McNutt, who is prominent not only in exploring the closest planet to Sol but also in planning a mission that would be our farthest yet, the Innovative Interstellar Explorer attempt to study nearby interstellar space. Fire and ice. McNutt (Johns Hopkins University Applied Physics Laboratory) obviously enjoys working at the extremes, and one hopes for an outcome for IIE just as successful as MESSENGER has enjoyed thus far. Meanwhile, Mercury looks more or less as expected, but don't let that fool you. As Greg Laughlin points out at his systemic site, we're looking at vast stretches of terrain that have never before been seen, our earlier views of Mercury having been delivered by Mariner 10 flybys that saw...

It's a long-term conundrum in interstellar studies: When do you launch a mission, knowing that faster methods may make your spacecraft obsolete? We might think about this problem again in light of Mike Gruntman's paper on a precursor interstellar mission to the local interstellar medium (LISM). As we saw on Friday, Gruntman (USC) has examined a probe to 400 AU, a region well outside the heliosphere where interstellar space is thought to be unperturbed by the Sun's influence. Keeping to technologies that are close to the required readiness level (he considers solar sails and nuclear electric propulsion), Gruntman works out a nominal escape velocity of 75 kilometers per second. To those who argue that a twenty-year mission to the 400 AU target is sure to be superseded by faster spacecraft, the counter-argument is clear: If we wait for a breakthrough, how do we know its timing? What if, Apollo-style, political decisions slow the development of sound alternatives? Incremental missions...

Imagine yourself aboard a spacecraft pushing into interstellar space. At what point would the Sun cease to be the brightest object in your sky? We're already looking at missions designed to study the local interstellar medium (LISM), with the goal of reaching anywhere from 300 to 400 AU, a region believed to be undisturbed by the Sun. From that range, the Sun still shows an apparent visual magnitude of -13.7, making it brighter than any other star we see from Earth (Sirius comes in at magnitude -1.46). So it's a long push. In fact, an early interstellar probe moving at 75 kilometers per second would have to travel six thousand years to reach the point where the Sun is no longer the brightest star. At 100,000 AU, which is 1.61 light years, our imaginary probe occupant would finally see a sky where the Sun was just another bright star. I get this information from a fascinating paper by Mike Gruntman (USC), who was kind enough to forward links not only to it but several other papers...

When the last Voyager pictures from Neptune (and perhaps even more eagerly awaited, the images of Triton) came in back in 1989, I distinctly recall the sense of letdown that set in the following week. All those spectacular Voyager findings were, I then assumed, a thing of the past. But as we've seen, the Voyagers are robust little spacecraft, pushing on toward the heliospause and the edge of interstellar space. Still functional, one or both may be sending us signals when they make this final transition within the next ten to twenty years. Which is not to say we don't need follow-up missions to explore this territory (Innovative Interstellar Explorer, using radioisotope methods to power an ion engine, immediately comes to mind), but what a grand story the Voyagers continue to write. And consider this finding: Because the two spacecraft took entirely different routes, Voyager 2 is crossing the termination shock region some 20 billion kilometers away from Voyager 1's present location....

When I use the term 'interstellar mission,' people assume I'm talking about a far future crewed mission to a star like Alpha Centauri or Epsilon Eridani. But the two Voyager spacecraft are on an interstellar mission of a sort, meaning they're eventually going to leave the Solar System entirely and head into true interstellar space. Because the Voyagers' power looks sound enough to keep sending data for another decade or more, we should thus get an interesting look at how our solar neighborhood differs from the medium that Sol and all the other stars in the Orion Arm swim in. Image: Voyager 1 and Voyager 2 leaving the solar system. Image Credit: NASA/Walt Feimer. The termination shock is that place where the solar wind -- charged particles flowing outward from the Sun -- slows below the speed of sound. It should be a tricky and mutable place, there being no fixed boundary out there some eight billion or so miles from our star. Instead, the termination shock should vary depending on...

The launch of the Dawn mission to the asteroids makes me think about solar sails. I realize that Dawn uses ion propulsion, about which more in a moment, but watching ion methods as they mature makes an emphatic point: We need to bring solar sail technologies up to the same readiness level that ion propulsion currently enjoys. And we need to be shaking out sail ideas in space. The Russian Znamya attempts at a 'space mirror' were attached to a Progress supply ship, and interesting mostly in terms of their deployment problems, leaving the 2004 Japanese test of reflective sails in space as the only free-flying experiments I know about. Which is not to say I'm a skeptic about ion propulsion. It will be fascinating to follow the performance of Dawn's engines as the mission progresses. 54 feet of solar array produce the needed power to ionize their onboard xenon gas, which is four times heavier than air. The ions are then electrically acccelerated and emitted as exhaust from the spacecraft....

Great to see Dawn on its way. The spacecraft lifted off at 11:34 UTC, with signal acquisition just over one hour into the flight. The spacecraft will begin its exploration of Vesta in 2011 and Ceres in 2015, two asteroids that between them have much to tell us about the history of the Solar System. Measurements of shape, surface topography, tectonic history, elemental and mineral composition will be included in a full data acquisition package. Image credit: NASA.

Physics breakthroughs aside, are there more conventional ways we can reach the stars? Centauri Dreams often cites (with admiration) Robert Forward's work on beamed laser propulsion, which offers a key advantage: The spacecraft need carry no bulky propellant. Forward's missions involved a 7200-GW laser to push a 785 ton unmanned probe on an interstellar mission. A manned attempt would involve a 75,000,000-GW laser and a vast vehicle of some 78,500 tons. The laser systems involved in such missions, while within our understanding of physics, are obviously well beyond our current engineering. Are there other ways to accomplish such an interstellar mission? One possibility is a hybrid system that combines what is known as Miniature Magnetic Orion technologies with beamed propulsion. The spacecraft would carry a relatively small amount of fission fuel, with the remainder of the propellant -- in the form of particles of fissionable material with a deuterium/tritium core -- being beamed to...