I often cite Robert Forward's various statements to the effect that "Travel to the stars is difficult but not impossible." Forward's numerous papers drove the point home by examining star travel through the lens of known physics, conceiving of ways that an advanced civilization capable of the engineering could build an interstellar infrastructure. But while Forward was early in this game, so were Iosif S. Shklovskii and Carl Sagan. A Russian astronomer, Shklovskii had written a book's whose Russian title translates roughly as 'Universe, Life, Intelligence' in 1962. Four years later, Sagan would join Shklovskii as co-author and the two would tackle the original book afresh, adding new material that reflected on and expanded the 1962 version's ideas. The result was the volume now called Intelligent Life in the Universe. I sometimes recommend books that are essential parts of a deep space library, and this is surely one, significant not only for its historical treatment of starflight...

Joseph Green worked for 37 years in the American space program, retiring from NASA as Deputy Chief of the Education Office at Kennedy Space Center. His specialty was preparing NASA fact sheets, brochures and other semi-technical publications for the general public, explaining complex scientific and engineering concepts in layman's language. Joe is the author of over 20 science papers for NASA and contractor executives, but I ran across him decades ago through his novel The Loafers of Refuge (Ballantine, 1965), a paperback that sits on my shelf not three feet from where I'm writing. Joe's five science fiction novels, which include Star Probe (1976) and Conscience Interplanetary (1972), are complemented by about 80 shorter works, and he remains active writing for online magazines, with recent stories in the February and May 2013 issues of Perihelion Science Fiction. As Joe explains, 31 years at Kennedy Space Center puts a wonderful spin on recent events. Sometimes the future happens...

Tracking Voyager 1 outbound for the past decade has been at times anti-climactic. Had the spacecraft reached interstellar space or hadn't it, and how exactly would we know? The announcement last week that the milestone has been reached will forever mark August 25, 2012 as the date when a human-built object, still returning data, made the crossing. That it took a year of analysis only reminds us how much we have to learn about even this closest region of the space between the stars, where some interactions with the Sun continue. "We have been cautious because we're dealing with one of the most important milestones in the history of exploration," said Voyager project scientist Ed Stone of the California Institute of Technology in Pasadena. "Only now do we have the data -- and the analysis -- we needed." Image: I use this image -- or one much like it -- all the time in my talks because it puts huge Solar System distances in perspective. The scale bar is measured in astronomical units...

Rachel Armstrong's presentation at Starship Congress so impressed me that I was quick to ask her to offer it here. I'm delighted to say that it will be only the first of what will become regular appearances in these pages. Much could be said about this visionary thinker, but here are some basics: Dr. Armstrong is co-director of AVATAR (Advanced Virtual and Technological Architectural Research) in Architecture & Synthetic Biology at The School of Architecture & Construction, University of Greenwich, London, a 2010 Senior TED Fellow, and Visiting Research Assistant at the Center for Fundamental Living Technology, Department of Physics and Chemistry, University of Southern Denmark. She completed clinical training at the John Radcliffe Medical School at Oxford in 1991, and in 2009 embarked on a PhD in chemistry and architecture at University College London. Perhaps only someone with this kind of diverse training could tackle the novel approach to building materials called 'living...

The progress of New Horizons through the outer Solar System has me thinking back to Voyager's great encounters. In 1986, when Voyager 2 whisked past Uranus, I was about to head off for a weekend of intensive work as a flight instructor -- a client we had contracted with had a large number of pilots in need of recurrent training, and I knew I would be in the cockpit well into each night, as indeed I was. Those long days and the memory of Voyager at Uranus are, of course, tinged with the explosion of Challenger, which took place a scant four days after Voyager's closest approach to the planet. We were all riveted by the coverage of the event but could only catch it in between training flights, but I remember trying to keep my mind off the fallen Shuttle as we dealt with constantly challenging weather over Maryland and West Virginia. And it was only later that I was able to really sit down and go over the images from Uranus, whose system of moons had always intrigued me -- it has...

The Voyager spacecraft have run into their share of problems as they move toward true interstellar space, but on the whole their continued operations have been a testament to what well designed equipment can do. Voyager 2's camera platform locked for a time not long after the Saturn flyby but controllers were able to restore the system by experimenting with similar actuators on Earth. Three years ago the craft began having data problems resulting from a flipped bit in an onboard computer but a reset from Earth corrected the fault. Even the failure of the primary radio receiver not long after launch was resolved by the use of the onboard backup. Obviously both craft are living on borrowed time as the power output of their radioisotope thermoelectric generators (RTGs) continues to decline, but we should still be getting signals for another decade or so. With the Voyagers now on what is designated their 'interstellar mission,' it's pleasing to note that Alpha Centauri is the guide star...

Konstantin Tsiolkovsky is the first person I know of to talk about worldships and their ramifications, which he did in an essay originally published in 1928. "The Future of Earth and Mankind" was the rocket pioneer's take on the need for enormous ships that could reach the stars in journeys taking thousands of years. The notion percolated quickly through science fiction, and by 1940 we have Don Wilcox's "The Voyage that Lasted 600 Years," which ran in Amazing Stories. Wilcox, who taught creative writing at Northwestern University, imagined a ship's captain who, though kept in hibernation, wakes up every 100 years to check on his ship, watching the gradual degeneration of the successive generations of the crew. It's a bleak take on worldship travel that has often been echoed in later science fiction. But would a worldship actually be this horrific, a cruise from hell that lasted entire lifetimes? See Ken MacLeod's Learning the World: A Novel of First Contact (2005) for the worldship...

If humans go out into the Solar System and beyond drawing on the resources they find along the way, they don't necessarily have to do it on worldships of the kind we talked about yesterday. But it's a reasonable assumption that creating large space habitats would make engineering projects in deep space easier to implement, housing workers and providing a base for operations. Ken Roy presented ideas about habitats in the Kuiper Belt at Huntsville, including the possibility of a large colony being created inside objects like Pluto. If we choose to go that route, we'll have the kind of space expertise to create artificial objects similar to worldships to help ourselves along. Of course, we hardly need to limit ourselves to the Kuiper Belt for this kind of thinking. Whatever the design of the ships we use, we can also consider expansion into the vast cometary resources of the Oort Cloud and any other objects that may lurk there, including so-called rogue planets. For years we've kicked...

Existential risks, as discussed here yesterday, seem to be all around us, from the dangers of large impactors to technologies running out of control and super-volcanoes that can cripple our civilization. We humans tend to defer thinking on large-scale risks while tightly focusing on personal risk. Even the recent events near Chelyabinsk, while highlighting the potential danger of falling objects, also produced a lot of fatalistic commentary, on the lines of 'if it's going to happen, there's nothing we can do about it.' Some media outlets did better than others with this. Risk to individuals is understandably more vivid. When Apollo 8 left Earth orbit for the Moon in 1968, the sense of danger was palpable. After all, these astronauts were leaving an orbital regime that we were beginning to understand and were, by the hour, widening the distance between themselves and our planet. But even Apollo 8 operated within a sequenced framework of events. Through Mercury to Gemini and Apollo, we...

I for one am astounded at the fact that it has been seven years since the launch of New Horizons. The craft, now more than halfway between the orbits of Uranus and Neptune, lifted off on January 19, 2006. I remember my frustration at having hundreds of cable channels on my television and not being able to see the New Horizons launch on any of them. I wound up tracking the event on a balky Internet transmission that, despite freezing up on more than one occasion, still got across the magic of punching this mission out into the deepest parts of the Solar System. With the flyby at Pluto/Charon in 2015, principal investigator Alan Stern is describing what his team is feeling as 'the seven year itch,' a sense of anticipation feeding off the spacecraft's continued good health along the way. Stern's latest report is online, noting that the current 'wake period' of the spacecraft (New Horizons was in hibernation from July of 2012 until January 6) is proceeding smoothly, including upload of...

Yesterday's look at radiation and its effects on humans in space asked whether any Fermi implications were to be found in the work described at the University of Rochester. One answer is that expansion into the cosmos does not need to be biological, for biological beings can build robotic explorers equipped with enough artificial intelligence to get the job done. A truly advanced civilization would be able to create large numbers of intelligent probes or, indeed, self-replicating probes that could spread throughout the galaxy on a timescale of perhaps ten million years. Fermi speculation is always fun but, when we get into the motivations of extraterrestrial civilizations, it leads inevitably to unfalsifiable solutions, good for conversation over coffee but incapable of producing a scientific result. Thus the 'zoo hypothesis,' the notion that the Earth is intentionally left alone to pursue its own development by beings with an agenda of their own. It makes for terrific science...

One rainy night in the mid-1980s I found myself in a small motel in the Cumberlands, having driven most of the day after a meeting and reaching Newport, TN before I decided to land for the night. It's funny what you remember, but small details of that trip stick with me. I remember the nicking of the wiper blades as I approached Newport, the looming shapes of the mountains in the dark, and most of all the fact that I was thinking about an interstellar mission. I was working on a short story that grew out of the Voyager mission and the experience of those who controlled it. After a late dinner at a restaurant near the motel, I asked myself what it would be like to be involved in a truly long-term mission. Suppose we develop the technologies to get a probe up to a few percent of the speed of light. If we send out a flyby mission to the nearest stars, we're talking about a couple of centuries of flight time, or maybe a bit less. It's inevitable, then, that a mission like this would be...

It was back in 1950 that Arthur C. Clarke looked at electromagnetic methods for getting a payload into space. The concept wasn’t new but Clarke’s paper in JBIS set out to examine what he saw as a practical use of it, an electromagnetic catapult on the lunar surface that could accelerate payloads back to Earth. The system was built around a three-kilometer long electromagnetic launcher that could accelerate payloads at 100 g’s to 2.3 kilometers per second (lunar escape velocity) in a matter of seconds. Gerard O’Neill thought such methods could deliver lunar raw materials to low Earth orbit for delivery to a space manufacturing site. Clarke’s ideas played naturally into O’Neill’s, for building large space habitats requires vast amounts of raw materials that we’d just as soon not have to lift out of Earth’s gravity well. But Clarke’s thinking wasn’t restricted to near-Earth uses of the technology. He saw no necessary limit to the lengths and accelerations that could be used. Provide...

While Rod Hyde, Lowell Wood and John Nuckolls were working on laser-induced fusion to drive a starship back in 1972, the range of options for advanced propulsion continued to grow. One we haven't talked about much in these pages is the use of gravitational slingshots in exotic settings. We're used to the concept within the Solar System because spacecraft like Voyager and Galileo have used a 'slingshot' around a planet to alter course and accelerate. But interstellar visionaries like Freeman Dyson have looked further out to imagine other uses for such techniques. In a 1963 paper, Dyson speculated on how an advanced civilization might use a binary star system made up of two white dwarfs. Send a spacecraft into the system for a close pass around one of the stars and, depending on the mass and orbital velocity of the stars, it is thrown out of the binary system at velocities as high as 3000 kilometers per second. But Dyson took the idea even further. His paper, which appeared as a...

Sara Seager's thoughts on who might join a crew bound for Alpha Centauri have had resonance, as witness Dennis Overbye's story Discovery Rekindles Wish for a Journey to the Stars in the New York Times. Overbye, a touchstone in science journalism, has probably been pondering the issue because of Seager's response to his question about Centauri B b. The MIT astronomer laid it out starkly: "I think we should drop everything and send a probe there." Seager is well aware of the issues involved and knows what a project it would be to drive a lightsail -- or some other kind of spacecraft -- up to ten percent of the speed of light. But she has us all thinking about the kind of people who would go on future manned missions (and whether they might wind up changing their minds). Overbye can look back at his high school yearbook, where he finds "Ambition: To go to the stars." These days he's thinking more about what would happen if he really did: Perhaps it is a sign of my age that I think more...

?If you were offered a chance to make an interstellar journey, would you take it? How about a garden-variety trip to low-Earth orbit? I’m often asked questions like this when I make presentations to the public, and I have no hesitation in saying no. Though I’m no longer doing any flight instructing, I used to love flying airplanes, but getting into a rocket and being propelled anywhere is not for me. To each his own: I’m fascinated with deep space and hope many humans go there, and you can count on me to write about their missions and robotic ones as well while keeping my office right here on Earth. The point is, the percentage of people who actually go out and take the incredible journeys and fly the dangerous missions is vanishingly low. But throughout history, there have always been a few intrepid souls who were willing to get into the canoes or the caravels or the biplanes and open up new territories and technologies. Thank God we have the Neil Armstrongs and Sergei Krikalyovs of...

Voyager 1, now 17 light hours from Earth, continues to be my touchstone when asked about getting to Alpha Centauri -- and in the last few days, I've been asked that question a lot. At 17.1 kilometers per second, Voyager 1 would need 74,000 years to reach the blistering orb we now believe to be orbiting Centauri B. Voyager 1 is not the fastest thing we've ever launched -- New Horizons at one point in its mission was moving with greater velocity, though no longer, and the Helios II Solar probe, no longer functional, reaches about 70 kilometers per second at perihelion. But Voyager 1 will be our first craft to reach interstellar space, and it continues to be a measure of how frustratingly far even the nearest stars happen to be. Cautionary notes are needed when a sudden burst of enthusiasm comes to these subjects, as it seems to have done with the discovery of Centauri B b. What we need to avoid, if we've got our eyes on long-term prospects and a sustained effort that may take centuries...

One of the challenges of explaining why a starship project is worth doing even though its final goal may not be realized for a long time is in showing how this work can have an impact on improving things on Earth. Technological spinoffs have acquired a bad name because of the stigma of Teflon and Tang -- NASA hasn't made the strongest case for how advanced work changes lives (and in any case, Teflon and Tang are not actually NASA spinoffs, though they are in the eyes of the public). But work in space can effect profound changes on Earth, and there is every reason to believe that energy breakthroughs in propulsion and power generation could be highly useful in solving our planet's future energy demands. [See the comments for a recent change to this text]. The list can obviously be expanded, as in the case of closed ecologies, which we've been talking about recently in these pages. A long-duration human mission demands attention to environments and their maintenance that will surely...

The continued explorations of our two Voyagers have earned these tough spacecraft the right to be considered an interstellar mission, which is how NASA now describes their journeys. Neither will come anywhere near another star for tens of thousands of years, but in this context 'interstellar' means putting a payload with data return into true interstellar space. Right now the Voyagers are still within the heliosphere, that great bubble opened out around our system by the Sun's solar wind, and the signs are multiplying that a transition is soon to occur. Three measurements are going to mark the boundary crossing, and we're seeing that two out of the three are in a state of rapid change. This JPL news release points out that on July 28, Voyager 1's cosmic ray instrument showed a jump of five percent in the level of galactic cosmic rays the craft was encountering. In the second half of that same day, the level of lower-energy particles flowing from inside the Solar System dropped by...

It's too bad we don't already have a workable Enterprise, that vast near-term rendition of the Star Trek vehicle that a systems engineer named 'Dan' has been talking about on BuildTheEnterprise.org (a site which has been so heavily trafficked in the last 48 hours that it has proven almost inaccessible). What Dan has in mind is the design, down to the smallest level of detail, of a ship powered by three ion propulsion engines that tap on-board nuclear reactors to remain operational. It may not be an antimatter-powered Enterprise, but it's a faithful simulacrum, reflecting its creator's long-lasting interest in the ship that William Shatner once commanded. Dan thinks the new Enterprise could get us to Mars in 90 days, but getting nuclear reactors into low Earth orbit in the first place will be a challenge not only technically but politically, and shielding the crew will also involve a serious amount of mass that has to get lifted. One of the fascinations of this highly detailed site is...