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Remembering Voyager: Triton’s New Map

by Paul Gilster | Aug 29, 2014 | Outer Solar System | 15 Comments

I'm glad to see Ralph McNutt quoted in a recent news release from the Johns Hopkins Applied Physics Laboratory. McNutt has been working on interstellar concepts for a long time, including the Innovative Interstellar Explorer mission that could become a follow-up to New Horizons. But he's in the news in late August because of Voyager, and in particular Voyager 2, which made its flyby of Neptune on August 25, 1989, some 25 years ago. McNutt recalls those days, when he was a member of the Voyager plasma-analysis team: "The feeling 25 years ago was that this was really cool, because we're going to see Neptune and Triton up-close for the first time. The same is happening for New Horizons. Even this summer, when we're still a year out and our cameras can only spot Pluto and its largest moon as dots, we know we're in for something incredible ahead." I can only envy someone who was up close with the Voyager outer planet flybys and is now a key player on New Horizons, for which McNutt leads...

Thinking about Magnetic Sails

by Paul Gilster | Aug 28, 2014 | Sail Concepts | 34 Comments

Magnetic sails -- 'magsails' -- are a relative newcomer on the interstellar propulsion scene, having been first analyzed by Dana Andrews and Robert Zubrin in 1988. We saw that the particle beam concept advanced by Alan Mole and discussed this week by Jim Benford would use a magsail in which the payload and spacecraft were encircled by a superconducting loop 270 meters in diameter. The idea is to use the magnetic field to interact with the particle beam fired from an installation in the Solar System toward the departing interstellar craft. Within our own system, we can also take advantage of the solar wind, the plasma stream flowing outward from the Sun at velocities as high as 600 kilometers per second. A spacecraft attempting to catch this wind runs into the problem that sunlight contains far more momentum, which means a magnetic sail has to deflect a lot more of the solar wind than a solar sail needs to deflect sunlight. A physical sail, though, is more massive than a spacecraft...

A Response to Comments on ‘Sails Driven by Diverging Neutral Particle Beams’

by Paul Gilster | Aug 27, 2014 | Sail Concepts | 15 Comments

Jim Benford's article on particle beam propulsion, published here last Friday and discussed in the days since, draws from the paper he will soon be submitting to one of the journals. I like the process: By running through the ideas here, we can see how they play before this scientifically literate audience, with responses that Jim can use in tweaking the final draft of the paper. Particle beam propulsion raises many issues, not surprising given the disagreements among the few papers that have tackled the subject. Are there ways of keeping the beam spread low that we haven't thought of yet? Does a particle beam require shielding for the payload? Does interplanetary particle beam work require a fully built infrastructure in the Solar System? We have much to consider as the analysis of this interesting propulsion concept continues. Dr. Benford is President of Microwave Sciences in Lafayette, California, which deals with high power microwave systems from conceptual designs to hardware....

Beaming to a Magnetic Sail

by Paul Gilster | Aug 26, 2014 | Sail Concepts | 8 Comments

Jim Benford's work on particle beam propulsion concepts, and in particular on the recent proposal by Alan Mole for a 1 kg beam-driven interstellar probe, has demonstrated the problem with using neutral particle beams for interstellar work. What we would like to do is to use a large super-conductor loop (Mole envisions a loop 270 meters in diameter) to create a magnetic field that will interact with the particle beam being fired at it. Benford's numbers show that significant divergence of the beam is unavoidable, no matter what technology we bring to bear. That means that the particle stream being fired at the receding starship is grossly inefficient. In the case of Mole's proposal, the beam size will reach 411 kilometers by the end of the acceleration period. We have only a fraction of the beam actually striking the spacecraft. This is an important finding and one that has not been anticipated in the earlier literature. In fact, Geoffrey Landis' 2004 paper "Interstellar Flight by...

Beamed Sails: The Problem with Lasers

by Paul Gilster | Aug 25, 2014 | Sail Concepts | 8 Comments

We saw on Friday through Jim Benford's work that pushing a large sail with a neutral particle beam is a promising way to get around the Solar System, although it presents difficulties for interstellar work. Benford was analyzing an earlier paper by Alan Mole, which had in turn drawn on issues Dana Andrews raised about beamed sails. Benford saw that the trick is to keep a neutral particle beam from diverging so that the spot size of the beam quickly becomes much larger than the diameter of the sail. By his calculations, only a fraction of the particle beam Mole envisaged would actually strike the sail, and even laser cooling methods were ineffective at preventing this. It seems a good time to look back at Geoffrey Landis' paper on particle beam propulsion. I'm hoping to discuss some of these ideas with him at the upcoming Tennessee Valley Interstellar Workshop sessions in Oak Ridge, given that Jim Benford will also be there. The paper is "Interstellar Flight by Particle Beam"...

Sails Driven by Diverging Neutral Particle Beams

by Paul Gilster | Aug 22, 2014 | Sail Concepts | 28 Comments

Is it possible to use a particle beam to push a sail to interstellar velocities? Back in the spring I looked at aerospace engineer Alan Mole’s ideas on the subject (see Interstellar Probe: The 1 KG Mission and the posts immediately following). Mole had described a one-kilogram interstellar payload delivered by particle beam in a paper in JBIS, and told Centauri Dreams that he was looking for an expert to produce cost estimates for the necessary beam generator. Jim Benford, CEO of Microwave Sciences, took up the challenge, with results that call interstellar missions into doubt while highlighting what may become a robust interplanetary technology. Benford's analysis, to be submitted in somewhat different form to JBIS, follows. by James Benford Alan Mole and Dana Andrews have described light interstellar probes accelerated by a neutral particle beam. I’ve looked into whether that particle beam can be generated with the required properties. I find that unavoidable beam divergence,...

Mapping the Interstellar Medium

by Paul Gilster | Aug 21, 2014 | Deep Sky Astronomy & Telescopes | 7 Comments

The recent news that the Stardust probe returned particles that may prove to be interstellar in origin is exciting because it would represent our first chance to study such materials. But Stardust also reminds us how little we know about the interstellar medium, the space beyond our Solar System's heliosphere through which a true interstellar probe would one day travel. Another angle into the interstellar medium is being provided by new maps of what may prove to be large, complex molecules, maps that will help us understand their distribution in the galaxy. The heart of the new work, reported by a team of 23 scientists in the August 15 issue of Science, is a dataset collected over ten years by the Radial Velocity Experiment (RAVE). Working with the light of up to 150 stars at a time, the project used the UK Schmidt Telescope in Australia to collect spectroscopic information about them. The resulting maps eventually drew on data from 500,000 stars, allowing researchers to determine...

To Build the Ultimate Telescope

by Paul Gilster | Aug 20, 2014 | Deep Sky Astronomy & Telescopes | 18 Comments

In interstellar terms, a 'fast' mission is one that is measured in decades rather than millennia. Say for the sake of argument that we achieve this capability some time within the next 200 years. Can you imagine where we'll be in terms of telescope technology by that time? It's an intriguing question, because telescopes capable of not just imaging exoplanets but seeing them in great detail would allow us to choose our destinations wisely even while giving us voluminous data on the myriad worlds we choose not to visit. Will they also reduce our urge to make the trip? Former NASA administrator Dan Goldin described the effects of a telescope something like this back in 1999 at a meeting of the American Astronomical Society. Although he didn't have a specific telescope technology in mind, he was sure that by the mid-point of the 21st Century, we would be seeing exoplanets up close, an educational opportunity unlike any ever offered. Goldin's classroom of this future era is one I'd like...

SETI: The Casino Perspective

by Paul Gilster | Aug 19, 2014 | Astrobiology and SETI | 69 Comments

I like George Johnson's approach toward SETI. In The Intelligent-Life Lottery, he talks about playing the odds in various ways, and that of course gets us into the subject of gambling. What are the odds you'll hit the right number combination when you buy a lottery ticket? Whenever I think about the topic, I always remember walking into a casino one long ago summer on the Côte d'Azur. I've never had the remotest interest in gambling, and neither did the couple we were with, but my friend pulled a single coin out of his pocket and said he was going to play the slots. "This is it," he said, holding up the coin, a simple 5 franc disk (this was before the conversion to the Euro). "No matter what happens, this is all I play." He went up to the nearest slot machine and dropped the coin in. Immediately lights flashed and bells rang, and what we later calculated as the equivalent of about $225 came pouring out. Surely, I thought, he'll take at least one of these coins and play it again --...

Did Stardust Sample Interstellar Materials?

by Paul Gilster | Aug 18, 2014 | Deep Sky Astronomy & Telescopes | 3 Comments

Space dust collected by NASA's Stardust mission, returned to Earth in 2006, may be interstellar in origin. We can hope that it is, because the Solar System we live in ultimately derives from a cloud of interstellar gas and dust, so finding particles from outside our system takes us back to our origins. It's also a first measure -- as I don't have to tell this audience -- of the kind of particles a true interstellar probe will encounter after it has left our system's heliosphere, the 'bubble' in deep space blown out by the effects of the Sun's solar wind. Image: Artist's rendering of the Stardust spacecraft. The spacecraft was launched on February 7, 1999, from Cape Canaveral Air Station, Florida, aboard a Delta II rocket. It collected cometary dust and suspected interstellar dust and sent the samples back to Earth in 2006. Credit: NASA JPL. The cometary material has been widely studied in the years since its return, but how to handle the seven potentially interstellar grains thus far...

A Dramatic Upgrade for Interferometry

by Paul Gilster | Aug 15, 2014 | Uncategorized | 12 Comments

What can we do to make telescopes better both on Earth and in space? Ashley Baldwin has some thoughts on the matter, with reference to a new paper that explores interferometry and advocates an approach that can drastically improve its uses at optical wavelengths. Baldwin, a regular Centauri Dreams commenter, is a consultant psychiatrist at the 5 Boroughs Partnership NHS Trust in Warrington, UK and a former lecturer at Liverpool and Manchester Universities. He is also a seriously equipped amateur astronomer -- one who lives a tempting 30 minutes from the Jodrell Bank radio telescope -- with a keen interest in astrophysics and astronomical imaging. His extensive reading takes in the latest papers describing optical breakthroughs, making him a key information source on these matters. His latest find could have major ramifications for exoplanet detection and characterization. by Ashley Baldwin An innocuous looking article by Michael J. Ireland (Australian National University, Canberra)...

What Io Can Teach Us

by Paul Gilster | Aug 14, 2014 | Outer Solar System | 8 Comments

Io doesn't come into play very much on Centauri Dreams, probably because of the high astrobiological interest in the other Galilean satellites of Jupiter -- Europa, Callisto and Ganymede -- each of which may have an internal ocean and one, Europa, a surface that occasionally releases material from below. Io seems like a volcanic hell, as indeed it is, but we saw yesterday that its intense geological activity produces interactions with Jupiter's powerful magnetosphere, leading to radio emissions that might be a marker for exomoon detection. The exoplanet hunt has diverse tools to work with, from the transits that result from chance planetary alignments to radial velocity methods that measure the motion of a host star in response to objects around it. Neither is as effective at planets in the outer parts of a solar system as we'd like, so we turn to direct imaging for large outer objects and sometimes luck out with gravitational microlensing, finding a planetary signature in the...

Radio Emissions: An Exomoon Detection Technique?

by Paul Gilster | Aug 13, 2014 | Exoplanetary Science | 12 Comments

Here's an interesting notion: Put future radio telescopes like the Long Wavelength Array, now under construction in the American southwest, to work looking for exomoons. The rationale is straightforward and I'll examine it in a minute, but a new paper advocating the idea homes in on two planets of unusual interest from the exomoon angle. Gliese 876b and Epsilon Eridani b are both nearby (15 light years and 10.5 light years respectively), both are gas giants, and both should offer a recognizable electromagnetic signature if indeed either of them has a moon. The study in question comes out of the University of Texas at Arlington, where a research group led by Zdzislaw Musielak is looking at how large moons interact with a gas giant's magnetosphere. The obvious local analogue is Io, Jupiter's closest moon, whose upper atmosphere (presumably created by the active volcanic eruptions on the surface) encounters the charged plasma of the magnetosphere, creating current and radio emissions....

‘Aragoscope’ Offers High Resolution Optics in Space

by Paul Gilster | Aug 12, 2014 | Deep Sky Astronomy & Telescopes | 12 Comments

Our recent discussions of the latest awards from the NASA Innovative Advanced Concepts office remind me that you can easily browse through the older NIAC awards online. But first a word about the organization's history. NIAC operated as the NASA Institute for Advanced Concepts until 2007 under the capable leadership of Robert Cassanova, who shepherded through numerous studies of interest to the interstellar-minded, from James Bickford's work on antimatter extraction in planetary magnetic fields to Geoffrey Landis' study of advanced solar and laser lightsail concepts. The NIAC Funded Studies page is a gold mine of ideas. NIAC has been the NASA Innovative Advanced Concepts office ever since 2011, when the program re-emerged under a modified name. NASA's return to NIAC in whatever form was a welcome development. Remember that we had lost the Breakthrough Propulsion Physics project in 2002, and there was a time there when the encouragement of ideas from outside the agency seemed...

Electric Sail Concept Moves Forward

by Paul Gilster | Aug 11, 2014 | Sail Concepts | 10 Comments

Just how we follow up on the investigations of New Horizons remains an open question. But we need to be thinking about how we can push past the outer planets to continue our study of the heliopause and the larger interstellar environment in which the Sun moves. I notice that Bruce Wiegmann, writing a precis of a mission concept called the Heliopause Electrostatic Rapid Transit System (HERTS) has drawn inspiration from the Heliophysics Decadal Survey, which cites the need for in situ measurements of the outer heliosphere and beyond. It's good to see a bit more momentum building for continuing the grand voyages of exploration exemplified by the Pioneers, the Voyagers and New Horizons. I often cite the Innovative Interstellar Explorer concept developed at Johns Hopkins (APL), which targets nearby interstellar space at a distance of over 200 AU, but whether we're talking about IIE or Claudio Maccone's FOCAL mission or any other design aimed at exiting the Solar System, the key problem is...

NIAC: An Orbiting Rainbow

by Paul Gilster | Aug 8, 2014 | Deep Sky Astronomy & Telescopes | 5 Comments

Remember Robert Forward's beamed sail concepts designed for travel to another star? Forward was the master of thinking big, addressing questions of physics which, once solved, left it up to the engineers to actually build the enormous infrastructure needed. Thus his crewed mission to Epsilon Eridani, which would demand not only a large power station in the inner system but a huge Fresnel lens out between the orbits of Saturn and Uranus. A 75,000 TW laser system was involved, a 'staged' sail for deceleration at the destination, and as for that lens, it would mass 560,000 tons and be a structure at least a third the diameter of the Moon. In addition to being a highly regarded physicist, Forward was also a science fiction writer who detailed his beamed sail concepts in Rocheworld (Baen, 1990), which grew out of a previous version in Analog. I always thought of the Epsilon Eridani mission as his greatest attempt to confound human engineering, but later came to think that vast structures...

Rosetta: Arrival at a Comet

by Paul Gilster | Aug 7, 2014 | Outer Solar System | 26 Comments

How do you close on a comet? Very carefully, as the Rosetta spacecraft has periodically reminded us ever since late January, when it was awakened from hibernation and its various instruments reactivated in preparation for operations at comet 67P/Churyumov-Gerasimenko. The spacecraft carried out ten orbital correction maneuvers between May and early August as its velocity with respect to the comet was reduced from 775 meters per second down to 1 m/s, which is about as fast as I was moving moments ago on my just completed morning walk. What a mission this is. When I wrote about the January de-hibernation procedures (see Waking Up Rosetta), I focused on two things of particular interest to the interstellar-minded. Rosetta's Philae lander will attempt a landing on the comet this November even as the primary spacecraft, now orbiting 67P/Churyumov-Gerasimenko, continues its operations. We're going to see the landscape of a comet as if we were standing on it, giving Hollywood special...

Keeping a Planet Alive

by Paul Gilster | Aug 6, 2014 | Exoplanetary Science | 28 Comments

I've made no secret of my interest in red dwarf stars as possible hosts of life-bearing planets, and this is partially because these long-lived stars excite visions of civilizations that could have a stable environment for many billions of years. I admit it, the interest is science fictional, growing out of my imagination working on the possibility of life under the light of a class of stars that out-live all others. What might emerge in such settings, in places where tidal lock could keep the planet's star fixed at one point in the sky and all shadows would be permanent? Some of this interest grows out of an early reading of Olaf Stapledon's 1937 novel Star Maker, in which the author describes life in the form of intelligent plants that live on such a tidally locked world. For that matter, Larry Niven developed an alien race called the Chirpsithra, natives of a red dwarf who have a yen for good drink and socializing with other species (you can sample Niven's lively tales of these...

What We Want to Hear

by Paul Gilster | Aug 5, 2014 | Culture and Society | 67 Comments

"A man hears what he wants to hear and disregards the rest." So sang Simon & Garfunkel in their 1968 ballad "The Boxer." Human nature seems to drive us to look for what we most want to happen. It's a tendency, though, that people who write about science have to avoid because it can lead to seriously mistaken conclusions. In science itself there is a robust system of peer review to evaluate ideas. It's not perfect but it's a serious attempt to filter out our preconceptions. As with the flap about 'faster than light' neutrinos at CERN, we want as many qualified eyes as possible on the problem. Journalists come in all stripes, but of late there has been a disheartening tendency to prove Paul Simon's axiom. Not long ago we went through a spate of news stories to the effect that NASA was investigating warp drive. True enough -- the Eagleworks team at Johnson Space Center, under the direction of Harold "Sonny" White, has been looking at warp drive possibilities for some time, though it...

Dining with Dirac

by Paul Gilster | Aug 1, 2014 | Culture and Society | 14 Comments

Ever wonder what it would have been like to sit in on a great occasion? I used to think about this in relation to a dinner party the painter Benjamin Haydon threw in 1817 at his London studio. At the 'immortal dinner' were, among others, William Wordsworth, John Keats and Charles Lamb, leading literary figures of their day. Fortunately, gatherings like these aren't relegated to the 19th Century. In a piece that ran originally in The New York Review of Science Fiction, Gregory Benford describes an equally extraordinary evening with some of the greatest minds of our time: Martin Rees, Stephen Hawking, and Paul Dirac. A physicist and award-winning science fiction writer, Benford relates the particulars of a Cambridge sabbatical as scientists at the top of their form meet for an evening of bonhomie, whimsy and reflection. by Gregory Benford In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before. But in poetry, it's the...

Charter

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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