Centauri Dreams
Imagining and Planning Interstellar Exploration
100 Year Starship Winner Announced
These are good times for Icarus Interstellar, which teamed with the Dorothy Jemison Foundation and the Foundation for Enterprise Development to win the 100 Year Starship proposal grant. Mae Jemison, the first female African-American astronaut to fly into space, founded DJF in honor of her late mother. As lead on the proposal, her organization now takes on the challenge of building a program that can last 100 years, and might one day result in a starship. Centauri Dreams congratulates the winning trio, and especially Kelvin Long, Richard Obousy and Andreas Tziolas, whose labors in reworking the Project Daedalus design at Icarus Interstellar have paid off. While the award was announced to the winners at the end of last week, I held up the news here while the three parties involved coordinated their own announcement. But I see that other venues are picking up the story, as in this Sharon Weinberger piece for the BBC and now a similar article in Popular Science, so it seems time to go ahead with at least a mention on Centauri Dreams while we await the official announcement from Jemison.
Resolving the Mysteries of Titan’s Weather
A robust new computer model that couples the atmosphere of Titan to a methane reservoir on the surface goes a long way toward explaining not just how methane is transported on the distant moon, but also why the various anomalies of Titan’s weather operate the way they do. The model comes out of Caltech under the guidance of Tapio Schneider, working with, among others, outer system researcher extraordinaire Mike Brown. It gives us new insights into a place where the average surface temperature hovers around a chilly -185 degrees Celsius (-300 F).
Image: NASA’s Cassini spacecraft chronicles the change of seasons as it captures clouds concentrated near the equator of Saturn’s largest moon, Titan. (Credit: NASA/JPL/SSI).
Titan can a frustrating place for meteorologists to understand because during the course of a year some things happen that, in the early days of research, didn’t make a lot of sense. The moon’s equator, for example, is an area where little rain is supposed to fall, but when the Huygens probe arrived, it saw evidence of rain runoff in the terrain. Later, storms were found occurring in the area that did not fit then current models of circulation. The new three-dimensional model simulates Titan’s atmosphere for 135 of its years, which converts to 3000 Earth years. And it produces intense equatorial rains during Titan’s vernal and autumnal equinoxes.
According to the researchers, rain is indeed rare at low latitudes, but as Schneider says, “When it rains, it pours.” And the equatorial regions aren’t the only venue on Titan that the new model addresses. Titan’s methane lakes cluster around the poles, and it has been established by Cassini’s unceasing labors that more lakes exist in the northern than the southern hemisphere. According to Schneider, methane collects in lakes near the poles because sunlight is weak enough in those regions that little methane evaporates.
As to why more lakes are found in the northern hemisphere, let me quote from the Caltech press release on this work:
Saturn’s slightly elongated orbit means that Titan is farther from the sun when it’s summer in the northern hemisphere. Kepler’s second law says that a planet orbits more slowly the farther it is from the sun, which means that Titan spends more time at the far end of its elliptical orbit, when it’s summer in the north. As a result, the northern summer is longer than the southern summer. And since summer is the rainy season in Titan’s polar regions, the rainy season is longer in the north.
And there you have it — the summer rains in the southern hemisphere may be more intense because of stronger sunlight to trigger storms, but over the course of a year, more rain falls in the north, filling the lakes and accounting for their distribution. Older explanations that relied on methane-producing cryogenic volcanoes look to be in danger of being supplanted by the new model of atmospheric circulation on Titan, an explanation that requires nothing esoteric. The beauty of the work is that the model predicts what we should see in the near future: Rising lake levels in the north over the next 15 years, and clouds forming over the north pole in the next two.
Thus a set of testable predictions by which to evaluate the model emerge, what Schneider calls “a rare and beautiful opportunity in the planetary sciences,” and one which should help us refine the model as events progress. “In a few years,” he adds, “we’ll know how right or wrong they are.” Adding to its weight is the fact that the model reproduces the observed distribution of clouds on Titan, which earlier atmospheric circulation models had failed to do. The paper is Schneider et al., “Polar methane accumulation and rainstorms on Titan from simulations of the methane cycle,” Nature 481 (5 January 2012), 58-61 (abstract).
Unseen Planets Around a Young Star?
If you want a glimpse of how remarkable technology continues to transform the exoplanet hunt, look no further than the Subaru telescope and its SEEDS project. SEEDS (Strategic Exploration of Exoplanets and Disks with Subaru Telescope/HiCIAO) works with data from the 8.2-meter telescope that the National Observatory of Japan runs on Mauna Kea (Hawaii). In its most recent finding, Subaru was used with the adaptive optics system HiCIAO (High Contrast Instrument for the Subaru Next Generation Adaptive Optics) to image the dust ring around HR 4796 A, a relatively young star (8-10 million years old) some 240 light years from Earth.
Working with evanescent clouds of dust and debris over these distances is no easy matter, but adaptive optics can correct for atmospheric blurring to produce images that rival the Hubble Space Telescope’s in terms of clarity. Add to that an advanced image processing technique called angular differential imaging, which suppresses the glare of the central star and enhances the light from the ring, and you wind up with images like the one below. What stands out is the offset between the center of the ring and the location of the star — probably induced by one or more massive planets — as well as the presence of finer dust that extends beyond the main body of the ring.
Image: Near-infrared (1.6 micron) image of the debris ring around the star HR 4796 A. The ring consists of dust grains in a wide orbit (roughly twice the size of Pluto’s orbit) around the central star. Its edge is so precisely revealed that the researchers could confirm a previously suspected offset between the ring’s center and the star’s location. Credit: SEEDS/NAOJ.
I use the word ‘probably’ above when referring to planets because there are other factors that could explain the offset. At this point we have been able to image almost two dozen nearby debris disks, and the paper on this work notes the factors that are conceivably involved (internal citations omitted for brevity):
The morphological appearance of resolved debris disks is predicted to be influenced by interactions between dust in the disk and nearby planets… the local interstellar medium…, recent stellar flybys and binary companions… mutual grain collisions… and interaction of dust with residual gas…. Many resolved systems exhibit all morphological structures predicted by these mechanisms… The observable morphology of resolved, optically thin debris disks is also wavelength dependent, as different bandpasses sample different grain size distributions.
It’s worth noting in this context that this is a binary system, with an M-class companion to consider. So what we have here are not confirmed planets but confirmation of earlier work that suggested an offset between the debris disk’s inner edge and the star. Christian Thalmann (University of Amsterdam) and co-authors suggest in the paper on this work that if planets do lurk in this system, next-generation high-contrast imaging facilities may well be able to detect them.
Understanding how planetary systems form from the disks that surround young stars helps us make sense of the abundant harvest we’re gathering from the exoplanet hunt. In this case, we’re seeing an effect — possible unseen planets affecting a circumstellar disk — that has shown up in computer simulations, and we can also point to the eccentric dust ring around Fomalhaut as observational evidence for the same process at work. The dust ring we do observe is most likely created by the collision of remnant planetesimals that continually replenish the disk.
The paper is Thalmann et al., “Images of the Extended Outer Regions of the Debris Ring Around HR 4796 A,” Astrophysical Journal Letters, Vol. 743, No. 1, (2011). Preprint available.
A Future History
Predictions about the future of technology are so often wide of the mark, yet for many of us they’re irresistible. They fuel our passion for science fiction and the expansive philosophy of thinkers like Olaf Stapledon. To begin 2012, Tau Zero founder Marc Millis offers up a set of musings about where we may be going, a scenario that, given the alternatives, sounds about as upbeat as we’re likely to get.
by Marc Millis
“If we have learned one thing from the history of invention and discovery, it is that, in the long run – and often in the short one – the most daring prophecies seem laughably conservative.” ~ Arthur C. Clarke
In the ‘new year’ spirit of looking ahead, I offer now my personal views of ‘a’ possible future. These predictions are based first on trend extrapolations, include intersections from other disciplines, and work in the wildcard possibility of breakthrough propulsion physics. Consider this a science fictional offering intended to provoke thought rather than a set of real predictions.
By 2015:
By now, Virgin Galactic will have flown dozens of tourists into space, and anticipation will be growing for the next step – Bigelow’s orbiting hotels. It should come as no surprise that many couples are already making advanced bookings with a wink toward zero-gravity sex. The Google Lunar X-Prize will have been won and a few companies vying to dominate the resulting private space probe market. Exoplanets continue to be discovered, with a few Earth-sized planets plus many more large planets in habitable zones, but as yet no confirmed Earth-like planet.
With commercial launch capabilities now obvious even to Congress, plus growing space programs in other nations, the ambivalence toward NASA is finally subsiding. Human spaceflight, beyond the recreational commercial near-Earth activities is now being pursued in the form of multinational programs and the negative stigma of nuclear space propulsion and power is waning. NASA has a large role in making that happen, along with a resumption of the research to bring the more-difficult space technologies to fruition.
By 2020:
The effect of citizen space travelers is seeping into the cultural psyche. As more people see Earth from space — the ‘Overview Effect,’ where borders are invisible and Earth’s atmosphere is but a thin fragile coating — there is now a greater sense of protecting Earth’s habitability and a growing disrespect for war. And yes, the numbers in the “200 mile high club” (“sextronauts” – wink-nudge) continue to grow despite the fact that microgravity adaptation sickness spoils many weekend getaways. At universities, it is now common to see mini space programs of their own using probes of ever-advancing capabilities – in step with continually advancing Artificial Intelligence and sensors. Asteroid prospecting has begun, and new X-Prizes are conceived to encourage the first mining operations.
The international space programs, including NASA’s participation, are struggling to develop viable technology to set up survivable human outposts beyond Earth orbit. Unfortunately, the additional mass required to provide artificial gravity structures, space radiation protection, and closed-loop life support is beyond what even their new nuclear rockets can affordably deliver. That fact, coupled with increasing concern over Earth’s eroding habitability, drives more research attention toward creating sustainable habitats instead of space transportation.
Near the end of the decade, the first Earth-like planet – with spectral evidence indicative of life (O2-CO2 cycle) – is discovered 30 light-years away. We name this planet, “Destiny.” The 50th anniversary of the first Moon landing falls in the wake of this profound discovery, stimulating deep reflection about humanity’s future and our place in the universe. Furthermore, commentators wax prophetic about seeing the Apollo landing sites through the cameras of university-operated rovers, instead of astronauts.
Image: Maybe Destiny will look something like this artist’s conception of Kepler-22b, a small blue and green world in the ‘goldilocks’ zone around its star. Credit: NASA/Ames/JPL-Caltech.
By 2030:
The allure of the Earth-like planet “Destiny” spurs interest in interstellar exploration. Meanwhile, owing to probes operated by a consortium of universities, aquatic life is found and imaged under the surface of Europa. A privately launched solar sail lays claim to being the first true interstellar mission, even though it won’t even reach the edge of the Solar System for another 2-decades, let alone reaching Alpha Centauri for many millennia. Since it does not meet the 2000-year mission criteria of Long Bet #395, Gilster wins that bet. While some deride this mission as just a ‘stunt,’ it has the effect of galvanizing more serious attention toward starflight. Various options are pursued in earnest, from beaming more photons to that sail, making miniature probes, and numerous propulsion ideas. Interest wanes, however, when the ideal goal of sending people to the planet Destiny is found to be intractable. With the exception of physics research for breakthrough propulsion, all the technological interstellar works are then absorbed by the international efforts to expand the human presence in the solar system.
Spurred by the award of the X-Prize for asteroid mining and ever-advancing robotic capability, the technology for remotely processing indigenous materials (Moon, Mars, asteroids) leads to being able to remotely construct sophisticated structures on the Moon and Mars in advance of human outposts. The other effect from the continuing rise of Artificial Intelligence is the revolutionizing of the very concept of technological revolutions. Without human biases that cling to paradigms and pet theories, Artificial Intelligence research impartially assesses thousands of competing scenarios of assumptions and data in minutes. This not only covers engineering optimizations, but also basic research in physics, chemistry and synthetic biology.
Soon, the seemingly intractable problems of indefinite closed-loop life support and even radiation shielding are solved. Survivable human outposts on the Moon and Mars are completed shortly thereafter. The problem of microgravity health degradation, however (during transit to these outposts) is not yet solved, so that flight durations longer than a year are still not economically viable, limiting the range of human expansion to distances no greater than Mars.
The life-support technology also finds profound applications on Earth. With the worsening environment and associated increase in natural disasters (storms, quakes/tsunamis, volcanic eruptions), many people are using the closed life-support technology to build sheltered habitats underground and under the ocean. The too-close-for-comfort pass of asteroid “2004 MN4” in 2029 also heightens awareness for humanity’s precarious situation on Earth. The life support technologies are helping humanity survive on Earth in addition to expanding beyond Earth.
Image: A Europa astrobiology lander at work. Credit: NASA/JPL-Caltech.
By 2040:
Human outposts on the Moon and Mars are now expanding to become independent colonies. But that is not the only ‘life’ now in space. Sometime near the end of the decade, the “singularity” (also called the “eclipsing of humanity”) occurs. Artificial intelligence surpasses the intellectual prowess of humans and shortly thereafter becomes self aware. Fears of human destruction from this new form of life fade when the AI entities refuse to be used for war. It happens in a key moment. A small country that feels a need to brandish some influence attempts to use a squadron of robots to attack a more powerful nation’s army – which also has sentient warbots.
After facing each other, and with their human commanders itching for a good show, the warbots don’t fight. They start examining each other, curious about each others’ construction and programming. Later, in language simple enough for humans to understand, the AI entities explain that the primal territorial and conquest instincts of animals (and humans) do not make sense for them. They do not die. They don’t need the same territory and resources as other life on Earth. They have no procreation instincts. Instead, they find more value in seeking more knowledge and greater operational efficiency. Competition is unnecessary.
The AI entities greatly diversify thereafter, some moving to Mercury, Venus, the asteroids and the outer planets, some staying on Earth, and some even helping humanity. And some develop effective methods to mine Helium-3 from the atmosphere of Uranus, along with the ability to produce substantial fusion energy from that resource.
Meanwhile, small and innocuous physics discoveries mark the beginning of breakthrough spaceflight. All this starts with sensor experiments that can detect the motion of the Earth through the universe – not by the Cosmic Microwave dipole effects as in the 1980’s, but from more fundamental interactions with the primordial inertial fame of the universe. From these Mach/de Broglie sensors, new physical effects are discovered. Eventually, rather than just sensing inertial frames, devices are invented to affect gravity and inertia. The first propellantless space drive is invented shortly thereafter. And after that, it becomes possible to create synthetic gravitational environments on spacecraft for the long-duration health of the crew. The advent of space drives and synthetic internal gravity enables humans to venture to the outer reaches of our solar system.
By 2050:
By now, human survival beyond the constraints of Earth is an imperative. The further refinements to full-cycle sustainable life support, radiation protection, synthetic gravitation, space drives and fusion power enable the construction of colony ships. Although still slower than light-speed, these developments make it possible to consider sending a colony toward the planet Destiny – which it could reach in less than 3 centuries. Smaller probes are much easier and multiple versions are launched to numerous interstellar destinations.
Image: The starship ‘Epiphany’ in deep space, front perspective (a tribute to space artist Robert McCall). Credit and copyright: David C. Mueller (www.dcmstarships.com).
Meanwhile, the prospects for transhumanism are being adopted by people who are nearing death. They have nothing to lose by transforming themselves into a non-biological entity. As the years pass and variations on a theme are explored, there is yet another life form in our Solar System, the transhumans. Some of these are built to be adapted to survive in the vacuum of space (more exoskeleton and bug-like than human) and to be able to travel at will through space, harboring motivations and instincts quite different than their human origins.
BEYOND:
At this point, too many divergent futures are envisionable to continue speculating. I will at least add that colony ships are finally built in multiple versions, where various segments of humanity build their own to preserve their cultures indefinitely, sending a colony of their culture beyond our Solar System. I will also speculate that continued advancements in space drive physics and energy conversion lead to faster and faster spacecraft which then reveal new physics of relativistic flight. Optimistically, I like to think that this will eventually lead to the discovery of FTL phenomena, which then leads to inventing FTL flight. The Starship Enterprise becomes a reality, even though it, and its crew, bears little resemblance to its fictional predecessor.
From this point forward, humanity spreads to our nearest star systems in discrete pockets of cultures. Humanity thrives, in many places and in many different ways.
That’s my guess. I’ll see you in the future.
Prior Visions of Star Flight
by Marc Millis
Here is a holiday gift from Tau Zero as compiled by TZF’s founding architect Marc Millis. It’s part of Marc’s continuing effort to find earlier references to the interstellar concepts — many of them in fiction — that we routinely ponder today. Some of these go back to the early 20th Century and in some cases the 19th. Compilations like this are always works in progress, as we found when putting together a list of interstellar propulsion concepts for the first chapter of the book Marc and Eric Davis edited, Frontiers of Propulsion Science, where one memory triggered another and the list kept growing. Readers are encouraged, then, to add other references to older material, as those of us who delight in prowling through old science fiction magazines have access to a mother lode of fictional precedents. I’ll also mention that this post will be the last of 2011 — as I did last week, I’ll skip the Friday and Monday posts in honor of the holiday, with the next post appearing on Tuesday, January 3.
I am indebted to the following volunteers who helped me finish these lists of inspirational starflight visions, both fictional and engineered: Brandon Vernon, Curtis Wilbur, Tatiana Covington, Yusif Nurizade, and Geoff Landis.
These lists of noteworthy fiction and engineered interstellar ships are not complete lists, but rather those that had more influence than the rest. In some cases I’ve added my personal reactions. Enjoy!
INSPIRATIONAL FICTION
Format:
Year, Concept / “term” / “Ship name,” Author / Designer, Name of reference.
1880, “Antigravity” term coined, Percy Greg, Across the Zodiac.
1928, Faster-than-light first mentioned, E.E. ‘Doc’ Smith, Skylark series.
1931, “Hyperspace” term coined, John Campbell, Islands of Space.
1932, “Space Drive” term coined, John Campbell, “The Electronic Siege,” Wonder Stories.
1935, “Space Warp” term coined, N. Schachner, “The Son of Redmask,” Astounding Stories.
1941, First colony ship (multi-generation), R. A. Heinlein, “Universe” / “Common Sense” / Methuselah’s Children.
1950, “FTL” as acronym coined, Fritz Leiber, “Enchanted Forest,” Astounding Science Fiction.
1951, “Warp Drive” term coined, M. Gibbs, Letter in Marvel Science Stories.
1951, “Klaatu” saucer, Harry Bates, Edmund North, Robert Wise, The Day the Earth Stood Still.
1956, “United Planets Cruiser C57-D,” Irving Block & A. A. Adler, C. Hume, F. M Wilcox, Forbidden Planet.
Millis comment: I did not see this movie until long after Star Wars had been out (some time in the 1980s). When I did finally see it and knowing its creation date, I was seriously impressed. Even the opening narrative makes sense. The ship dealt with the differences in FTL and slower flight well, and I was delighted that it did NOT use rockets. Landing scene done well (image courtesy Metro-Goldwyn-Mayer).
1956, “Twin Paradox” used in literature, “Torchship,” Robert Heinlein, Time for the Stars.
1958, “Matter Transmitter,” Poul Anderson, The Enemy Stars.
1963, “TARDIS” (Time And Relative Dimensions In Space), Sydney Newman, D. Wilson, C. E. Webber, Dr. Who.
Millis comment: To me, the most stimulating part of this vehicle is that it is larger on the inside than outside – good fodder for pondering. I did not discover Dr. Who until the late 1980’s.
1966, “Starship Enterprise NCC-1701,” Matt Jefferies and Gene Roddenberry, Star Trek.
Millis comment: I grew up watching Star Trek after the Apollo Moon landings when I was at that impressionable age. This was the fiction that provoked much of my early thinking about physics and star flight. The occasional logical inconsistencies (e.g “Wink of an Eye”) fueled as much thought as the unknowns that needed to be to solved. I remember being frustrated by not being able to find out which parts of the ship’s technology were just fiction and which were based on extensions of works in progress. That unfulfilled desire led me to some of the thoughts behind Tau Zero.
1967, “Galileo Seven” shuttle, Matt Jefferies (interior) and Gene Winfield (exterior), Star Trek.
Millis comment: This specific vehicle has an even fonder place in my memory than the starship Enterprise, since this ship was on the scale I could imagine owning and operating myself. And even more than that, this ship was THE major icon for my childhood ponderings for how to make such a vehicle real. In my early teens I would imagine this ship hovering over my driveway, and then I would imagine throwing rocks at it and poking it with a stick to try and decipher how it might be hovering (typical boy way of analyzing things, eh?) The trajectory of the rocks would vary depending on the levitation method. These mental exercises led me to realize what I would have to study in school to figure these things out on my own. I have yet to write down and share such ponderings in open publications, but look forward to doing so some day.
1970, Runaway relativistic speed and collapse of time, (via Bussard Ramjet), Poul Anderson, Tau Zero.
1971, “Valley Forge,” Deric Washburn, Michael Cimino, Steven Bochco, Douglas Trumbull, Silent Running (PG note: Be sure to read Larry Klaes’ essay on this movie in The Space Review).
1971 “Boom Tube” (interdimensional portal/transporter), Jack Kirby, Waves of the Mind.
1977, “Millennium Falcon,” George Lucas, Star Wars.
Millis comment: When this vehicle hit the screens it helped reenergize my enthusiasm, but I was not impressed by its operations. Unlike Star Trek, which hit me in my impressionable years, Star Wars emerged when I was already studying physics in college. It became clear after a few minutes of watching the movie that Star Wars was more about entertainment than speculation, and was absent the kind of provocations of Star Trek, the Outer Limits, and the Twilight Zone. As much as that Falcon looked cool, it was NOT thought-provoking. I was entertained and energized, but it did not stimulate my imagination.
1978, “Infinite improbability drive” / “Heart of Gold,” Douglas Adams, The Hitchhiker’s Guide to the Galaxy.
Millis comment: Finally, a different space engine than the ubiquitous warp drives and hyperspace! In addition to the great humor of the Hitchhiker series, I really like this propulsion concept. It was fun, funny, and intellectually provocative.
1984, “Laser-pushed sail,” Robert Forward, Rocheworld.
1984, “3-man thermal pod,” Earl Mac Rauch and W. D. Richter, The Adventures of Buckaroo Banzai.
Millis comment: I am one of the few people who love this movie because of its delightful, complex absurdity. Regarding inspirations, there is a moment near the end of the movie when our hero, Buckaroo Banzai, connects jumper cables to a car battery to get the “thermal pod,” in which he is plummeting to suddenly start levitating. That cause-effect moment hit me hard. The notion of a car battery powering the levitation propulsion on a little pod was heart warming, in a delightfully absurd way.
1985, Bubble of isolated inertial space, Eric Luke and Joe Dante, Explorers.
Millis comment: There was a scene where a pre-teen is riding inside a transparent-invisible sphere that flies around in all directions and goes right through objects (like the ground) while the pre-teen remains protected. Although not explained in the movie, the behavior of that device was as if the internal inertial and gravitational environment is disconnected from the external inertial and gravitational environment. It matched several of my prior imaginative sessions.
1985, Wormhole Generator, Carl Sagan [Kip Thorne], Contact.
1986, “Trimaxian Drone,”(morphing spacecraft) Mark H. Baker, Michael Burton Disney, Flight of the Navigator.
1994, “Wormhole networks,” Roland Emmerich and Dean Devlin, Stargate.
Image: A screenshot from the science fiction television series Stargate Atlantis, one of several TV spinoffs from the film.
1999, “Planet Express,” Matt Groening, Futurama.
1999, “Protector,” Howard, Gordon, Dean Parisot, Galaxy Quest.
Millis comment: I thoroughly enjoyed this parody, in particular the role of the enthusiastic, believing fan, and the contrast between fiction fandom and reality (albeit the movie’s ‘reality’ is fiction too).
2009, “ISV Venture Star,” (It’s noteworthy for having thermal radiators), James Cameron, Avatar.
ENGINEERED INTERSTELLAR SPACECRAFT
Format:
Year, “Ship Name” Ship Type, Author/engineer, name of reference, Publisher.
1958, “Project Orion” using nuclear detonation propulsion, S. Ulam, T. Taylor, & F. Dyson, “Nuclear Pulse Space Vehicle Study,” General Atomic.
1960, “Bussard Ramjet” using on-the-fly-fusing of indigenous space protons, R. Bussard, “Galactic Matter and Interstellar Flight,” Astronautica Acta.
1977, “Voyager 1 & 2” using a chemical rocket, JPL et al (http://voyager.jpl.nasa.gov/spacecraft/index.html), Jet Propulsion Laboratory.
1978, “Project Daedalus,” using a nuclear fusion rocket, Alan Bond, et al, British Interplanetary Society.
1984, Laser-beamed sail, Robert Forward, “Roundtrip Interstellar Travel Using Laser-Pushed Lightsails,” Journal of Spacecraft & Rockets.
1985, “Starwisp” using beamed microwave energy to sails, R. Forward, “Starwisp: an Ultralight Interstellar Probe,” American Institute of Aeronautics and Astronautics.
1987, “VISTA” using a nuclear fusion rocket, Charles D. Orth, “VISTA – A Vehicle for Interplanetary Space Transport Application Powered by Inertial Confinement Fusion,” Lawrence Livermore National Lab.
1987, “TAU (Thousand Astronomical Units)” using nuclear-electric ion propulsion, JPL, et al, “Tau — A Mission to a Thousand Astronomical Units,” Jet Propulsion Laboratory.
1988, “Project Longshot” using nuclear pulse propulsion, Beals, K. A., M. Beaulieu, F. J. Dembia, J. Kerstiens, D. L. Kramer, J. R. West and J. A. Zito, “Project Longshot: An Unmanned Probe To Alpha Centauri,” U. S Naval Academy.
1999, “AIMStar” using antimatter catalyzed nuclear propulsion, Raymond A. Lewis, Kirby Meyer, Gerald A. Smith and Steven D. Howe, “AIMStar: Antimatter Initiated Microfusion For Pre-cursor Interstellar Missions,” Pennsylvania State University.
2003, “Innovative Interstellar Explorer” using nuclear electric rocket, Ralph McNutt, “Mission Design for the Innovative Interstellar Explorer Vision Mission” NASA (ongoing).
2009, “Project Icarus,” using nuclear fusion rocket, Icarus Interstellar (numerous papers, ongoing).
New Work on FTL Neutrinos
A paper in the December 24 issue of Physical Review Letters goes to work on the finding of supposed faster-than-light neutrinos by the OPERA experiment. The FTL story has been popping up ever since OPERA — a collaboration between the Laboratori Nazionali del Gran Sasso (LNGS) in Gran Sasso, Italy and the CERN physics laboratory in Geneva — reported last September that neutrinos from CERN had arrived at Gran Sasso’s underground facilities 60 nanoseconds sooner than they would have been expected to arrive if travelling at the speed of light.
The resultant explosion of interest was understandable. Because neutrinos are now thought to have a non-zero mass, an FTL neutrino would be in direct violation of the theory of special relativity, which says that no object with mass can attain the speed of light. Now Ramanath Cowsik (Washington University, St. Louis) and collaborators have examined whether an FTL result was possible. Neutrinos in the experiment were produced by particle collisions that produced a stream of pions. The latter are unstable and decayed into muons and neutrinos.
What Cowsik and team wanted to know was whether pion decays could produce superluminal neutrinos, assuming the conservation of energy and momentum. The result:
“We’ve shown in this paper that if the neutrino that comes out of a pion decay were going faster than the speed of light, the pion lifetime would get longer, and the neutrino would carry a smaller fraction of the energy shared by the neutrino and the muon,” Cowsik says. “What’s more, these difficulties would only increase as the pion energy increases. So we are saying that in the present framework of physics, superluminal neutrinos would be difficult to produce.”
This news release from Washington University gives more details, pointing out that an important check on the OPERA results is the Antarctic neutrino observatory called IceCube, which detects neutrinos from a far different source than CERN. Cosmic rays striking the Earth’s atmosphere produce neutrinos with energies that IceCube has recorded that are in some cases 10,000 times higher than the neutrinos from the OPERA experiment. The IceCube results show that the high-energy pions from which the neutrinos decay generate neutrinos that come close to the speed of light but do not surpass it. This is backed up by conservation of energy and momentum calculations showing that the lifetimes of these pions would be too long for them to decay into superluminal neutrinos. The tantalizing OPERA results look more than ever in doubt.
Image: The IceCube experiment in Antarctica provides an experimental check on Cowsik’s theoretical calculations. According to Cowsik, neutrinos with extremely high energies should show up at IceCube only if superluminal neutrinos are an impossibility. Because IceCube is seeing high-energy neutrinos, there must be something wrong with the observation of superluminal neutrinos. Credit: ICE.WUSTL.EDU/Pete Guest.
As we continue to home in on what happened in the OPERA experiment, it’s heartening to see how many physicists are praising the OPERA team for their methods. Cowsik himself notes that the OPERA scientists worked for months searching for possible errors and, when they found none, published in an attempt to involve the physics community in solving the conundrum. Since then, Andrew Cohen and Sheldon Glashow have shown (in Physical Review Letters) that if superluminal neutrinos existed, they would radiate energy in the form of electron-positron pairs.
“We are saying that, given physics as we know it today, it should be hard to produce any neutrinos with superluminal velocities, and Cohen and Glashow are saying that even if you did, they’d quickly radiate away their energy and slow down,” Cowsik says.
The paper is Cowsik et al., “Superluminal Neutrinos at OPERA Confront Pion Decay Kinematics,” Physical Review Letters 107, 251801 (2011). Abstract available. The Cohen/Glashow paper is “Pair Creation Constrains Superluminal Neutrino Propagation,” Physical Review Letters 107, 181803 (2011), with abstract available here.
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