Paul Gilster | Centauri Dreams

Lightsails: Safe Passage After All?

by Paul Gilster | Apr 16, 2012 | Sail Concepts | 22 Comments

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...

Collisions in the Interstellar Medium

by Paul Gilster | Apr 13, 2012 | Interstellar Medium | 28 Comments

Memories play tricks on us all, but trying to recall where I saw a particular image of a laser lightsail is driving me to distraction. The image showed a huge sail at the end of its journey, docked to some sort of space platform, and what defined it were the tears and holes in the giant, shredded structure. It presupposed long passage through an interstellar medium packed with hazards, and although I assumed I would have seen it on the cover of some science fiction magazine, I spent an hour yesterday scanning covers on Phil Stephensen-Payne’s wonderful Galactic Central site, but all to no avail. The image must have run inside a magazine, then, but if so, I’m at a loss to identify it other than to say it would have appeared about twenty years ago. I had hoped to reproduce it this morning because our talk about starship shielding necessarily brought up the question of whether an enormous lightsail -- some of these are conceived as being hundreds of kilometers in diameter -- wouldn’t be...

Lasers: Protecting the Starship

by Paul Gilster | Apr 12, 2012 | Interstellar Medium | 23 Comments

Interesting new ideas about asteroid deflection are coming out of the University of Strathclyde (Glasgow), involving the use of lasers in coordinated satellite swarms to change an asteroid's trajectory. This is useful work in its own right, but I also want to mention it in terms of a broader topic we often return to: How to deal with the harmful effects of dust and interstellar gas on a fast-moving starship. That's a discussion that has played out many a time over the past eight years in these pages, but it's as lively a topic as ever, and one on which we're going to need a lot more information before true interstellar missions can take place. Lasers and the Asteroid But let's set the stage at Strathclyde for a moment. The idea here is to send small satellites capable of formation flying with the asteroid, all of them firing their lasers at close range. The university's Massimiliano Vasile, who is leading this work, says that the challenge of lasers in space is to combine high power,...

The Largest Solar System Yet

by Paul Gilster | Apr 11, 2012 | Exoplanetary Science | 21 Comments

The Kepler mission's exoplanet discoveries have been so numerous that an extension of the mission seemed all but inevitable. At the same time, bureaucracies can be unpredictable, which is why it was such a relief to have the Senior Review of Operating Missions weighing in with an extension recommendation, one followed up by NASA with extensions not just for Kepler but also for the Spitzer telescope and the US portion of ESA's Planck mission. Kepler's extension runs through fiscal 2016 (subject to review in 2014), allowing for plenty of time to home in on Earth-sized planets in the habitable zone around stars like our Sun. While Kepler's scheduled mission duration was 3.5 years, the mission was intended to be extendible to 6 years or more and this news is more than satisfying. But of course while we continue to monitor the Kepler work, we're following numerous other exoplanet stories including the European Southern Observatory's observations of the prolific star HD 10180, a Sun-like...

Splashdown on Titan?

by Paul Gilster | Apr 10, 2012 | Outer Solar System | 14 Comments

Getting to the stars may involve a sudden breakthrough -- we can't rule out disruptive technologies, nor can we predict them -- but my guess is that interstellar flight is going to be a longer, more gradual process. I can see a sort of tidal expansion into the outer system, forays to Mars, for example, followed by reassessment, retrenchment, then one day deeper study of Jupiter's moons with advanced robotics that can get under Europa's ice. The search for life may become so provocative that we have to explore Titan and Enceladus with human crews, and the imperative for planetary protection may help us further tune up our deep space technologies. The thing is, one wave of exploration inevitably begets another. Let's put no timeframe on that kind of expansion because, like the tides, it may surge at times and then fall back, hostage to budgetary problems and waves of public interest that can as easily ebb. But I could see an eventual civilization that extends throughout the Solar...

Reasons for a Human Future in Space

by Paul Gilster | Apr 9, 2012 | Outer Solar System | 38 Comments

I closed last week with two posts about the AVIATR mission, an unmanned airplane that could be sent to Titan to roam its skies for a year of aerial research. It’s a measure of Titan’s desirability as a destination that it has elicited so many mission proposals, and I want to get into the Titan Mare Explorer (TiME) as well, but let’s pause a moment to consider the nature of what we’re doing. Out of necessity, all our missions to the outer system have been unmanned, but as we learn more about long-duration life-support and better propulsion systems, that may change. The question raised this past weekend in an essay in The Atlantic is whether it should. Ian Crawford, a professor of planetary sciences at Birkbeck College (London) is the focus of the piece, which examines Crawford’s recent paper in Astronomy and Geophysics. It’s been easy to justify robotic exploration when we had no other choice, but Crawford believes not only that there is a place for humans in space, but that their...

A Closer Look at the Titan Airplane

by Paul Gilster | Apr 6, 2012 | Outer Solar System | 11 Comments

Yesterday's discussion of the AVIATR mission to Titan inevitably brought up another prominent Titan mission concept: Titan Mare Explorer (TiME). I'll have more to say about this one next week, as today I want to continue talking about AVIATR, but you can once again see how Titan enthralls us with its 'Earth-like' aspects. Need a thick atmosphere around a moon? Titan is your only play, and if, as with TiME, you want to put an instrument package into an off-planet surface lake, you'll be hard pressed to do it anywhere else, at least in this Solar System. These two mission concepts fire the imagination -- they're the kind of thing kids like me used to dream about when we plunked down our money at the newsstand for copies of Galaxy or Fantasy & Science Fiction. It's unlikely, though, that both missions will fly. If TiME, which is a Discovery-class mission finalist and thus cost-capped at $425 million, is chosen, then the odds on AVIATR probably drop. AVIATR, a New Frontiers-class...

AVIATR: Roaming Titan’s Skies

by Paul Gilster | Apr 5, 2012 | Outer Solar System | 13 Comments

Each of our highest priority targets in the outer Solar System offers something unique, from Europa’s internal ocean to the geysers of Enceladus. But Titan exerts the kind of fascination that comes from the familiar. The imagery of lakes and river channels reminds us inescapably of our home world, even if the temperature on the Saturnian moon averages a brisk 94 K, which works out to -291 degrees on the Fahrenheit scale. But because of its thick atmosphere we have options for exploring Titan that are unavailable on the other icy moons, and we’re working with a landscape that is a compelling frozen doppelgänger of Earth, a landscape we’d like to explore up close. As we saw yesterday, part of the outer system puzzle is getting supplies of plutonium-238 up to speed, and there is at least some movement on that front. If we want to get aggressive about exploring Titan, one excellent way to deploy that plutonium is aboard AVIATR (Aerial Vehicle for In-situ and Airborne Titan...

Plutonium-238 and the Outer System

by Paul Gilster | Apr 4, 2012 | Missions | 13 Comments

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...

Planets Around an Ancient Star

by Paul Gilster | Apr 3, 2012 | Exoplanetary Science | 32 Comments

The idea of 'deep time' exerts an abiding fascination. H.G. Wells took us forward to a remote futurity when his time traveler looked out on a beach dominated by a red and swollen Sun. But of course deep time goes in the other direction as well. I can remember wanting to become a paleontologist when I discovered books about the world of the dinosaurs, my mind reeling from the idea that the world these creatures lived in was as remote as any distant star. Paleontology was a grade-school ambition I never followed up on, but the Triassic and Jurassic eras still have a hold on my imagination. In a SETI context, deep time presents challenges galore. Charles Lineweaver's work offers up the prospect that the average Earth-like planet in our galactic neighborhood may well be far older than our own -- Lineweaver calculates something like an average of 1.8 billion years older. Would a civilization around such a star, if one could survive without destroying itself for so long, have anything it...

Re-Thinking The Antimatter Rocket

by Paul Gilster | Apr 2, 2012 | Antimatter | 27 Comments

Once when reading Boswell's monumental life of the 18th Century writer and conversationalist Samuel Johnson, I commented to a friend how surprised I had been to discover that Johnson didn't spend much time reading in his later years. "He didn't need a lot of time," replied my friend, a classics professor. "He tore the heart out of books." That phrase stuck with me over the years and re-surfaced when I started working with Adam Crowl. More than anyone I know, Adam can get to the heart of a scientific paper and explain its pros and cons while someone like myself is still working through the introduction. And because of his fine work with Project Icarus, I thought Adam would be just the person to explain the latest thinking about a classic concept that Friedwardt Winterberg would like to take to the next level. by Adam Crowl In Jules Verne's From the Earth to the Moon, the bold Frenchman Michel Ardan, in his first speech to the Baltimore Gun Club, when discussing travelling to the Moon...

Correction re WISE

by Paul Gilster | Apr 2, 2012 | Administrative | 3 Comments

Last week I reported on information from a source on the WISE mission that no new red dwarfs had yet been discovered out to a distance of 10 light years. This past weekend I received an email from my source apologizing for mis-typing. He had meant to say no brown dwarfs -- not red dwarfs -- out to a distance of 10 light years. And as I mentioned with the earlier post, the data analysis continues and there may be surprises yet to come. A nearby brown dwarf is something I've been writing about here for some time, pondering its implications and wondering whether one might actually turn up that was closer than the Alpha Centauri stars. So the news is that no brown dwarfs matching the description have yet turned up, but the hunt continues.

Interstellar (Precursor) Mission & Vehicle Design

by Paul Gilster | Mar 30, 2012 | Uncategorized | 39 Comments

by Marc Millis Tau Zero's first graduate student project has been completed. Berkeley Davis, a 2nd Lt. at the United States Air Force Institute of Technology, Dayton Ohio, completed his Masters thesis on a deep space probe to perform Claudio Maccone's gravitational lens mission (FOCAL). For those unfamiliar with FOCAL, it is a mission to utilize the gravitational lens effect that begins at approximately 550 AU from the Sun, one that in the view of Maccone will offer huge magnifications for the study of targets like the Cosmic Microwave Background. For more, see the Centauri Dreams archives. IMPETUS Maccone, Deep Space Flight and Communications: Exploiting The Sun as a Gravitational Lens (Springer, 2009). MISSION/VEHICLE STUDY Davis, Berkeley. R. (2012) Gravitational Lens: The Space Probe Design (Thesis), AFIT/GA/ENY/12-M06, Air Force Institute of Technology. To provide a realistic baseline on what is possible, the student was asked to constrain his design to commercially...

ESO: Habitable Red Dwarf Planets Abundant

by Paul Gilster | Mar 29, 2012 | Exoplanetary Science | 45 Comments

Red dwarfs are all over the news thanks to an announcement by the European Southern Observatory. Results from a new HARPS study show that tens of billions of planets not much larger than Earth are to be expected in the habitable zones around this class of star. The finding reinforces the growing interest in M-class stars and becomes especially interesting when you realize that faint red stars like this make up as much as 80 percent of the stars in the Milky Way. That leaves plenty of room for astrobiology, depending on factors we need to discuss below. Do we suddenly have a close destination for a potential interstellar probe? Well, Barnard’s Star has always been in the running for an early mission because of its relative proximity to us at 5.94 light years. But we still have no word on planets there (despite a much publicized but soon discredited set of observations from a 1969 paper). Proxima Centauri is available at 4.2 light years, but we have yet to learn whether it has planets....

An Interstellar Reminiscence

by Paul Gilster | Mar 28, 2012 | Culture and Society | 2 Comments

by A. A. Jackson Although it was probably science fiction that got Al Jackson into interstellar flight, he remembers discovering the work of Eugen Sänger back around 1960 and becoming energized to seek out the few scientific papers on relativistic rocket designs that were then available. With a firm background in engineering, he turned to physics in 1975, receiving a PhD from the University of Texas at Austin, a natural move for a man who had worked for NASA during the heyday of Apollo as astronaut trainer on the Lunar Module Simulator. Going through Al’s papers is a fascinating exercise in its own right, but I was reminded because of our recent articles on Robert Bussard’s ramjet ideas that Al had worked with Daniel Whitmire. Bussard spoke about fusing protons in his ramscoop engine, but subsequent analysis showed that the power needed to compress protons to fusion densities far outweighed the power that would be produced. It was Daniel Whitmire who developed the ‘catalytic ramjet’...

Catalyzed Fusion: Tuning Up the Ramjet

by Paul Gilster | Mar 27, 2012 | Missions | 18 Comments

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...

A Brief Window: The Bussard Ramjet in the 1960s

by Paul Gilster | Mar 26, 2012 | Culture and Society | 18 Comments

It's fascinating to watch how expansive ideas take hold in the public imagination. The idea of a starship that could scoop up particles from the interstellar medium came to Robert Bussard while he was at Los Alamos Scientific Laboratory and, as we saw recently in our articles on slowing down a starship, became the basis for subsequent magsail concepts because Bussard's design evidently generates far more drag than effective thrust. But before the problems of the design became widely known, Walter Sullivan, a writer for the New York Times, had brought the ramjet into play for future human journeys to the stars in a book called We Are Not Alone (definitely not the same book as the 2011 title by Dirk Schulze-Makuch). Subtitled 'The Continuing Search for Extraterrestrial Intelligence' in its latest revision, the original 1964 book was written at a time when SETI was an infant discipline (although the later revision goes through the Drake equation and places SETI in the context of...

Century of the Starship

by Paul Gilster | Mar 23, 2012 | Culture and Society | 33 Comments

I once thought about putting together a collection of classic papers on interstellar flight. It would start with early work by the likes of Les Shephard, Eugen Sänger and Carl Wiley (whose groundbreaking paper on solar sails appeared not in a scientific journal but in Astounding Science Fiction). The book would proceed with the key papers of Forward, Bussard and Dyson and move into papers from the Project Daedalus report, then to Matloff and Mallove and up to the present day, with a long look at the Italian solar sail work of Vulpetti, Maccone and Genta. Especially later in this period there is abundant material to choose from, and there's Alcubierre to consider, and Millis' work with the Breakthrough Propulsion Physics project. And then there's Geoff Landis and Robert Frisbee and the closely reasoned sociological analyses of Michael Michaud and... Well, you can see what happens when you start pondering editing possibilities. The book is already growing to enormous size and I've done...

Crowd-Funding the Exomoon Hunt

by Paul Gilster | Mar 22, 2012 | Astrobiology and SETI | 27 Comments

I've been trying to figure out why exomoons -- moons around planets that orbit stars other than our own -- have such a fascination for me. On the purely scientific level, the sheer amazement of discovery probably carries the day, meaning that I grew up in a time long before we had confirmation of any exoplanets, and now we're talking about getting data on their moons. But there's also that sense of the exotic, for we can wonder whether gas giants in the habitable zone, which may be more plentiful than we realize, might have life on their own rocky moons. David Kipping (Harvard-Smithsonian Center for Astrophysics) has been a key player in the exomoon hunt for some time now (search under his name in the archives here and you'll retrieve articles going back for years). David is now working with a 'crowd-funding' source called Petridish.org to fund a new mini-supercomputer that will go to work on the Hunt for Exomoons with Kepler (HEK) project. The idea behind HEK is to use Kepler data...

Starship Surfing: Ride the Bow Shock

by Paul Gilster | Mar 21, 2012 | Interstellar Medium | 26 Comments

We've been looking at slowing down a starship, pondering ways the interstellar medium itself might be of use, and seeing how the stellar wind produced by the destination star could slow a magsail. A large solar sail could use stellar photons, but the advantage of the magsail is that it's going to be effective at a greater distance, and we can also consider other trajectory-bending effects like the Lorentz turning studied by Robert Forward and P.C. Norem. But if you take a look at the relevant papers on magsails and other uses of the medium, you'll find that they all assume the interstellar medium is more or less uniform. We know, of course, that it is not. For one thing, the Sun itself seems to be near the boundary of the Local Interstellar Cloud, and there are a number of such clouds within about 5 parsecs of the Solar System. In fact, we're not exactly sure whether the Sun is just outside the LIC or barely within it. In any case, as Ian Crawford has pointed out, Centauri A and B...

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In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

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