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...

What would you do if you had a spacecraft pushing toward the edge of the Solar System with nothing much to do? The answer is to assign it an extended mission, as we found out with the two Voyagers and their continuing data return that is helping us understand the boundaries of the heliosphere. In the case of New Horizons, NASA's probe to Pluto/Charon, two extended missions may be involved after Pluto, the first being a flyby of one or more Kuiper Belt targets, the second being a further look at what is actually going on where the solar wind meets the interstellar medium. Alan Stern, principal investigator for New Horizons, comments on the possibility in his latest report on the mission, noting that a second extended mission isn't out of the question, and adding that New Horizons won't make it as far as the Voyagers before it runs out of power. But 90 to 100 AU seems a possibility, which would provide a useful supplement to Voyager data. Remember that New Horizons carries two...

by Andreas Hein The immense problems of time, distance and life support invariably mean that when we talk about an interstellar mission, we talk about robotics. But the imaginative team at Icarus Interstellar, which is now setting up projects on everything from beamed lightsails (Project Forward) to pulse propulsion engines (Project Helios), has pushed into the biggest what-if of all, the question of manned missions. And as project leader Andreas Hein reminds us in the following article, a variety of approaches have been suggested for this over the years from which a new concept study can grow. Andreas Hein received his master's degree in aerospace engineering at the Technische Universität München, and is doing his PhD at the same university in the area of space systems engineering at the Institute of Astronautics. He has participated in several mission studies: a lunar gravity measurement mission by EADS and a cubesat mission analysis. During his internship at ESA-ESTEC, he...

Powering up a spacecraft is a lot easier to manage in the Sun-rich environment inside the orbit of Mars than it is out past the orbit of Jupiter. Solar panels provide plenty of power for a satellite in near-Earth orbit, for example, but moving into the outer system invokes the need for RTGs -- radioisotope thermoelectric generators -- powered by radioactive decay. If you read through the specs on the FOCAL mission design presented here last Friday, you saw that this attempt to reach the Sun's gravitational lens would demand 20 RTGs, and thus requires resumed production of plutonium-238. What's happened is that US production of 238Pu was halted as far back as 1988, leaving us with stockpiles that should be sufficient for missions in the pipeline through the end of this decade. That's the view of Leonard Dudzinski, NASA's Radioisotope Thermoelectric Generator program executive, who was speaking at the opening session of the 43rd Lunar and Planetary Science and the Nuclear and Emerging...

Long-time Centauri Dreams readers have learned to tolerate my eccentricities (or, at least, they’re kind enough not to dwell on them). One of them is my love of poking around in old books related to space travel, which is how Benjamin Field’s A Narrative of the Travels and Adventures of Paul Aermont Among the Planets (1873) recently caught my eye. I don’t know much about Field other than that he chose to produce this tale of interplanetary wanderings under a pseudonym, but what’s fun about his tale is that after his journeys to Jupiter, Saturn, Mars and Venus are over, Field’s protagonist returns to Earth to find that the planet is fully fifty years older, though he himself has aged hardly at all. Time dilation, the reader might say, but of course Field wouldn’t have known anything about special relativity. It’s fun to consider, though, how an idea that in 1873 would have been simple fantasy -- that someone might travel at high speed and age at a different rate than those he left...