by Paul Gilster | Jan 23, 2009 | Advanced Rocketry |
by Adam Crowl
In the market for a mammoth starship? Recently released work by Friedwardt Winterberg, discussed here by Adam Crowl, points to fast interplanetary travel and implies possibilities in the interstellar realm that are innovative and ingenious. Adam notes in an e-mail that Winterberg’s drive has certain similarities to MagOrion, a system that in its earliest iteration combined a magnetic sail with small yield nuclear fission devices. Dana Andrews and Robert Zubrin first published that concept in 1997 and it has been evolving in the years since, but Winterberg’s work takes the idea into the realm of what may be a truly workable fusion design. Read on as we follow up our earlier story on Winterberg with a much deeper look.
Friedhardt Winterberg has worked on inertial confinement fusion since 1954 and was extensively involved in developing new fusion devices during the Cold War alongside bomb-makers like Edward Teller. Much of his non-fission triggering work was classified, but his declassified suggestions in 1970 for setting off fusion reactions via electron beams were adopted by the British Interplanetary Society’s “Daedalus” starprobe study, with all that implies for the interstellar community.
However, Winterberg says in his new papers, electron beams just won’t work when triggering deuterium reactions. This is an important point. Bombs have typically used deuterium-tritium (D-T) reactions, but these release 80% of their energy as neutrons – useless for rockets and problematic for power generation. Pure deuterium (D-D) reactions are a better option and have been successfully triggered in bombs – the 15 megaton “Mike” test is one example – but they require a more intense burst of energy to cause a sufficiently rapid and energetic collapse to produce fusion in the target material. Something like a gigajoule of energy must be concentrated on the deuterium target within less than a tenth of a micro-second to produce fusion and not merely blow the target apart in a puff of hot gas.
Image: Friedwardt Winterberg, whose innovative propulsion concept now weds magnetic mirror technologies with fusion. Credit: Wikimedia Commons.
How to do so with present day technology and apply it successfully to rockets requires overcoming some serious problems. An intense proton-beam sufficiently rapidly acting to cause the fusion-making implosion has a beam-power of an unprecedented 10 petawatts (10,000 trillion Watts.) For it to rise to full power sufficiently rapidly – in less than a 1/10th of a microsecond – a voltage of a billion Volts is needed, which in a terrestrial laboratory would cover the machinery in gigantic sparks due to insulation breakdown of the surrounding air. How to avoid such wasteful artificial lightning?
In a vacuum the issue is less serious. Large voltages can be maintained by firing off charge as electron beams or small charged pellets. Winterberg imagines a spaceship wrapped in a set of superconducting coils to maintain the gigantic charge needed and create a magnetic mirror. Then a laser beam blasts a plug of solid hydrogen in the fuel target producing a jet of protons as a bridge between the ship and the target. This allows the massive charge of the ship to discharge as the desired high-energy proton-beam with sufficient power to collapse the deuterium fuel. The resulting fusion explosion produces a huge plasma wave that the ship’s magnetic mirror now deflects, transferring momentum from the plasma to the ship. Winterberg also discusses a means of triggering the same reaction in an atmosphere – via ultraviolet argon lasers.
Winterberg is very critical of current efforts to compress fusion fuel via lasers because to be sufficiently energetic the lasers would be destroyed in the process. Winterberg turns this problem into a virtue by using an explosion-pumped laser-beam – a shaped cylinder of hexogen explosive detonates at 8 km/s and compresses a rod of solid argon, thus pumping its atoms into a UV laser-emitting state. This intense UV laser-beam then compresses a deuterium-tritium fuel target that in turn causes a bigger D-D fusion explosion. All this now rapidly expanding plasma, plus air sucked into the reaction chamber, now explodes out the rocket nozzle as a high-speed exhaust.
Image: Superconducting “atomic” spaceship, positively charged to GeV potential, with azimuthal currents and magnetic mirror M by magnetic field B. F fusion minibomb in position to be ignited by intense ion beam I, SB storage space for the bombs, BS bioshield for the payload PL, C coils pulsed by current drawn from induction ring IR. e electron flow neutralizing space charge of the fusion explosion plasma. Credit: Friedwardt Winterberg.
So what sort of performance is expected? Winterberg’s interplanetary vehicle has an exhaust velocity of 100 km/s, while the launcher vehicle gets 10 km/s. Sufficient to industrialise the Solar System, Winterberg’s stated goal, but what of interstellar travel? Small fusion bombs in the right casing can trigger bigger explosions, thus potentially we have the makings of (large) starship fusion-triggering system.
Imagine an Orion or even Daedalus style vehicle, large enough to magnetically contain the fusion explosions more efficiently than the external fusion system Winterberg describes. To get the high performance fusion plasma need for starflight most of the propellant plasma has to be products of the reaction, not incidentals like the disintegrated argon laser or the fusion target chamber that contains the deuterium. The more diluted the mix, the slower the exhaust. Very large bombs are less diluted, but need larger vehicles to contain their blast. Thus Winterberg style starship-building potentially necessitates the gargantuan.
The Winterberg paper is “Deuterium microbomb rocket propulsion,” available online. The original MagOrion paper is Andrews and Zubrin, “Nuclear Device-Pushed Magnetic Sails (MagOrion),” American Institute of Aeronautics and Astronautics Paper 97-3072, 33rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Seattle, Washington, 1997.
by Paul Gilster | Jan 22, 2009 | Deep Sky Astronomy & Telescopes, Exotic Physics |
Understanding how galaxies form is no easy matter, particularly when you factor in dark matter. Without a firm knowledge of what dark matter actually is, we’re limited to discussing its perceived effects, something that researchers at Hebrew University of Jerusalem have coupled with computer simulations that change how we view the early universe.
The large galaxies some three billion years after the Big Bang apparently didn’t form from the merger of smaller disks of material, says this team. That earlier theory would have seen slow star formation as the various disks eventually came together. But the latest observations show that early galaxies created stars at a rapid rate. The new theory may explain why. It sees galaxies forming as the result of cold hydrogen flowing in narrow streams along the filaments of the so-called ‘cosmic web’ that defines the large scale structure of matter in the universe.
These hydrogen streams would feed into the halos of dark matter that are believed to enshroud the forming galaxies, helping the emergence of a rotating disk at the center. The computer models show that this continuing infall of cold gas produces a scenario that promotes star formation.
In fact, the Hebrew University team has worked out a physical theory that traces the formation of gas clumps in the early disks and shows how such cosmic streams could drive them. What’s especially interesting is that the theory offers a way to explain the formation of elliptical galaxies in the early universe. These are the galaxies, far more rounded in shape than spirals like the Milky Way, that house predominately old, red stars.
Image: Computer simulation of galaxy formation shows matter flowing into the center of a galaxy through three cold gas streams. Such pictures provide the basis for the new theory of galaxy formation via these streams. Credit: The Hebrew University of Jerusalem.
It’s fascinating stuff, incorporating as it does the latest thinking on dark matter. But it’s also a reminder of how much we still have to learn about dark matter itself as we put these simulations to further tests. What breakthroughs may lie ahead as we continue to study what this mysterious ‘stuff’ is will keep us pursuing dark matter stories in these pages.
The paper is Dekel, “Cold streams in early massive hot haloes as the main mode of galaxy formation,” Nature 457 (January 22, 2008), pp. 451-454 (abstract). A Hebrew University news release is here.
by Paul Gilster | Jan 21, 2009 | Exoplanetary Science |
Could we find evidence of vegetation on distant exoplanets? The answer may be yes, according to recent work by Luc Arnold (Observatoire de Haute Provence) and team. If green vegetation on another planet is anything like what we have on Earth, then it will share a distinctive spectral signature called the Vegetation Red Edge, or VRE. The new paper creates climate simulations that explore whether planets with a distinctively different climate than modern Earth’s could be so detected.
Two earlier eras are useful here. The Last Glacial Maximum (LGM) occurred 21,000 years ago, with global temperatures on the order of 4 degrees Celsius colder than today, and a significantly lower sea level that produced more land surface. The Holocene, 6,000 years ago, is marked by a rising sea level amidst the de-glaciation occurring in the northern hemisphere. Perhaps the most striking contrast with today would be the Sahara, much more laden with vegetation than at any time since. Both provide a useful contrast with data gathered for the modern Earth. Thus:
The mid-Holocene is dominated by a greening of the Sahara, and a poleward shift of the high latitude treelines. The LGM is characterised by a large expansion of steppe and grassland vegetation at mid-latitudes, with a near disappearance of temperate forest. There is also the fragmentation of tropical forest and widespread expansion of tundra vegetation at high latitudes. There are, however, some disagreements with the data, for example the expansion of grassland in Australia.
This is fascinating stuff in its own right, as a look at the image below suggests, with its story of climate change on our planet. Check the paper for the full map legend. Today’s Earth is shown at the top:
Image: Maps of biomes today (top), 6 kyrBP during the Holocene optimum (middle) and 21 kyrBP during the LGM (bottom), with continental and sea ices. Note that 6 kyrBP, a large part of the Sahara displayed a temperate grassland biome and almost no barren regions, while today and at 21 kyrBP, it consists of barren and desert (shrubland and steppe) landscapes. Credit: Luc Arnold and team.
In each climatic scenario, the model had to be adjusted for cloud cover and its reflectance, a fact Arnold’s team handled by using data from the International Satellite Cloud Climatology Project. This is highly complex modeling that must take in ocean and sea ice — I leave you to the paper for the methodological details. The primary result is encouraging: “…climate differences between the Quaternary extrema and the modern Earth’s climate have little impacts on the vegetation signal, since the spectral signature of vegetation is not washed out during the LGM and does not increase very much during the Holocene optimum.”
Meanwhile, what are the possibilities for an early detection of such worlds? An Earth-like planet in the habitable zone is 1010 fainter than its parent star as viewed from Earth. So the probability is not high with a first generation terrestrial planet finder instrument in the 4-meter range. In fact, a 6-meter telescope is apparently the minimum for detecting seasonal variations. But closer, larger planets may work. A super-Earth within 6 parsecs may be within reach of a smaller space-based coronagraph in terms of detecting a basic VRE signature.
And the kind of space-based interferometer — an array of small telescopes — envisioned as a successor to early planet finder missions may do much better. Read this remarkable paragraph carefully:
Hypertelescopes in space – interferometric sparse arrays of small telescopes – will indeed allow us to see Earth-like planets as small resolved disks several resels across… and this clearly will help us to detect photosynthetic life on these planets! For example, a 150-km hypertelescope would provide 40 resolution elements (resels) across an Earth at 3 pc in yellow light… And a formation of 150 3-m mirrors would collect enough photons in 30-min to freeze the rotation of the planet and produce an image with at least ≈ 300 resels, and up to thousands depending on array geometry… At this level of spatial resolution, it will be possible to identify clouds, oceans and continents, either barren or perhaps (hopefully) conquered by vegetation.
Will something like the planet in the image at left swim into view? We can only imagine, but there is every reason to believe that terrestrial class worlds are not uncommon, and as we noted yesterday, the discovery of one with a life signature would energize research and provoke renewed public attention to the myriad worlds around us. As the authors note, a next step for this work would be to extend the studies into even older epochs, when climates were more extreme than those considered here, to understand how stable a signature VRE can provide.
Image: Simulated image of the Earth at 3 pc (10 light-years) observed with a 150-km hypertelescope interferometric array made of 150 3-m mirrors working at visible wavelengths. North and South America are visible. Note that this simulation is done at visible wavelengths, while in the (very) near-IR at 750 nm, vegetated areas would be much brighter and more easily detectable on continents. Spatial resolution at 750 nm would remain the same than at visible wavelength with the same hypertelescope flotilla being spread over 225-km instead of 150-km. Credit: Luc Arnold and team.
The paper is Arnold et al., “The Earth as an extrasolar planet: The vegetation spectral signature today and during the last Quaternary climatic extrema,” accepted by the International Journal of Astrobiology and available online.
by Paul Gilster | Jan 20, 2009 | Culture and Society, Exoplanetary Science, Sail Concepts |
What would it take to energize the public about interstellar flight? The answer seems obvious: Discover an Earth-type planet around another star. As happened with Gliese 581 c, once thought to be potentially habitable, the media would quickly focus on the question of how to get there. Interviewed by the BBC on that topic, I found myself explaining that a star over twenty light years away was an impossible target at our current level of technology, but the discussion quickly opened up into what we could do about that, and what methods might evolve to allow star travel.
The point is to get people thinking not only about distances but methods. Right now we’re still in the ‘build a better rocket’ mindset, one that doesn’t comprehend the realities of adding more fuel just to push still more additional fuel. The equations are inexorable: Rockets can’t do the job when we’re talking about crossing light years, so we look for ways to leave the propellant at home. And because even fast solar sails are numbingly slow at Centauri distances, we consider beamed propulsion via lasers, microwaves and particle beams, and look into the possibilities of antimatter through near-term technologies like Steve Howe’s antimatter catalyzed sail. And, of course, we hope for breakthroughs beyond.
Image: Or maybe an interstellar ramjet? Like other interstellar technologies, the idea has severe problems and may not be workable. But getting the public energized about these issues is one way to ensure that research continues and new ideas emerge. Credit: Manchu/ITSF.
Now comes the news that a planet discovered through microlensing — MOA-2007-BLG-192-L b — orbits not a brown dwarf, as originally believed, but an M-class dwarf, a larger star whose mass in turn suggests that the planet is smaller than first thought. MOA-2007-BLG-192-L b, in fact, could weigh in at about 1.4 Earths, and that, as this New Scientist story explains, would make it unusually interesting (but see the addendum below). The magazine quotes Scott Gaudi (Ohio State):
“The result is important because this is the lowest-mass planet yet detected, and is extremely close to the mass of the Earth,” he says. “Obviously, finding a true Earth-mass planet is one of the biggest goals of searches for exoplanets. We are very close to that goal now.”
Gaudi is not himself a member of this team, which is led by Jean-Philippe Beaulieu (Paris Astrophysical Institute); Beaulieu recently reported on the new findings at a meeting of the Royal Astronomical Society in London. Following up that story led me to the microlensing team Beaulieu heads. Called HOLMES (Hunting fOr Low Mass Extrasolar planetS), its stated goal is “…the discovery of low mass planets (1 – 15 Earth masses) within 1 – 5 AU of the most common stars in our Galaxy by microlensing effects in order to measure their frequency.”
Surely Scott Gaudi is right that we are close to finding an Earth-mass planet, and one day after that, a team like Beaulieu’s may turn up one in the habitable zone of its star. An intense round of media interest will inevitably follow.
The question: Will the discovery of an Earth-analog elsewhere in the galaxy be a one-day event, to be eclipsed by still more ‘breaking news’ in the perpetually overheated reporting cycle? Chances are it will, but my hope is that each intriguing exoplanet discovery will give us a brief window to work on public awareness of Earth’s place in the cosmos. If we choose to become a star-faring species, it will be because on the broadest possible level we will have placed ourselves in the context of a galaxy that may well be aswarm with living worlds. The key is to get people thinking, one story, one idea, one planet at a time.
Addendum: Re the mass of MOA-2007-BLG-192-L b, be sure to read David Blank’s message below. New Scientist‘s story was in error — the true mass seems to be 3.3 (+4.9 / – 1.8) Earth masses.
by Paul Gilster | Jan 19, 2009 | Deep Sky Astronomy & Telescopes |
A familiar scenario from the early universe is getting a tune-up. It’s long been believed that cosmic dust was first produced by supernovae, becoming the essential building block for the formation of planets. New work using the Spitzer Space Telescope suggests a second mechanism that complements the first. So-called ‘carbon stars,’ stars late in their lives and similar to red giants but containing more carbon than oxygen, may have played as significant a role as supernovae themselves.
The work focused on the carbon star MAG 29, some 280,000 light years away in the Sculptor Dwarf galaxy. Says Albert Zijlstra (Jodrell Bank Centre for Astrophysics):
“All the elements heavier than helium were made after the Big Bang in successive generations of stars. We came up with the idea of looking at nearby galaxies poor in heavier elements to get a close-up view of how stars live and die in conditions similar to those in the first galaxies.”
Image (click to enlarge): The star MAG 29, shown in relation to the Sculptor Dwarf. Credit: Anglo-Australian Observatory.
This look back in time could offer clues to the formation of our own world. The existence of carbon stars in early galaxies was thought unlikely until now, but MAG 29 is found in a galaxy that contains only four percent of the carbon and other heavy elements seen in the Milky Way. It’s similar, in other words, to the primitive galaxies under active investigation at the far reaches of the universe. Learning how carbon stars contribute to dust in ancient galaxies should firm up our understanding of how these stars and their galaxies evolve. Thus Gregory Sloan (Cornell):
“We haven’t seen carbon-rich dust in this primitive an environment before. What this tells us is that carbon stars could have been pumping out dust soon after the first galaxies were born.”
It’s also interesting that MAG 29 is exceptionally rich in hydrocarbons, vital components of life’s appearance. Once again we look at phenomena in the distant universe whose chemical signature reminds us of the factors that produced life on our own planet. If we’re not inside a cosmos that is teeming with life, the real problem may be explaining why not. But is intelligence a natural outcome, and does it invariably lead to technology?
The paper in Science appears as the International Year of Astronomy launches with opening ceremonies at UNESCO headquarters in Paris. Science‘s own cover marking the event is a spectacular Spitzer image of dust clouds in the center of the Milky Way. The carbon star paper is Sloan et al., “Dust Formation in a Galaxy with Primitive Abundances,” Science Vol. 323, No. 5912 (January 16, 2009), pp. 353-355 (abstract). A Science & Technology Facilities Council news release is also available.
