Centauri Dreams
Imagining and Planning Interstellar Exploration
The Asteroid Deflection Gambit
We’ve talked often in these pages about Near Earth Objects (NEOs) and the potential danger posed not just by them but by objects from much further out in the Solar System if they were to take an Earth-crossing trajectory. But it’s also true that NEOs have a certain allure even if they are potentially dangerous. They’re close enough to consider a manned mission, and even a small 2-kilometer sized metallic NEO could contain rich metals and minerals worth trillions of dollars. Of course, what metals markets would do if we suddenly had access to such an object is another matter. And mining an NEO, not a new concept, is still on the impractical side.
But Hexi Baoyin (Tsinghua University, Beijing) and colleagues are proposing a possible solution. The temporary capture into Earth orbit of an NEO by creating a small velocity change could allow a relatively low-cost trajectory to the object that would provide mining opportunities. And indeed, various asteroid deflection schemes from solar radiation to nuclear explosions are available in the literature, most considered in terms of saving our planet from an impact. The authors of this new paper (thanks to Phil Mowatt for the tip) have set about identifying what it would take to capture an NEO to Earth orbit, using as their case in point a periodic comet called 39P/Oterma.
It’s an interesting object, this Oterma, one that sometimes is captured by Jupiter for one to several orbits. Call it a ‘temporary moon.’ In the same way, the authors believe that ‘a small velocity increment’ would be enough if exerted in the right place to cause the temporary capture of a NEO in Earth orbit. They acknowledge that the method would work only for small NEOs, based on our current technology, with the larger ones being too heavy for significant change to their orbital energy.
How to cause the desired effect? The authors look at alternatives from nuclear explosions and kinetic impactors (impulsive) to Yarkovsky effect, focused solar, gravity tractor, mass driver, pulsed laser and space tug (slow push) before settling on one from the first camp:
Considering the required impulsive velocity increment is not so small and the diameter of NEOs is relatively large, there are two impulsive capture methods available, kinetic impactor and nuclear explosion, but they are never tested or applied. Among them, the nuclear explosion method may not be proper one for the mentioned small NEO, because the nuclear explosion can release a very large amount of energy, the result may be a fragmentation of the target NEO. So the kinetic impactor is often considered as a better maneuver means especially for the NEOs smaller than 50 meters in diameter.
So we’re talking about a space probe or projectile that would hit the NEO at high velocity and change its orbit. A possible candidate is the smallish asteroid 2008EA9, but the list of candidates is growing as our surveys continue. The new orbit would be a temporary one but would allow a prolonged period of study and, possibly, exploitation of resources there. All of which jogged my memory of Carl Sagan’s work with JPL’s Steven Ostro on precisely these matters. One paper devoted to the problem was “Cosmic Collisions and the Longevity of Non-Spacefaring Galactic Civilizations” (citation below). Two matters come to mind in relation to it, the first being the need to deal with space debris over the long haul, which Sagan and Ostro handle thusly:
Sooner or later human civilization must confront the asteroid/comet collision hazard or become extinct. Dealing with interplanetary collision hazards over a period of centuries or millennia will naturally take our spacefaring society further out into the solar system — if for nothing else, to improve surveillance of incoming comets. As technology advances and the life-span of our species (and its successors) lengthens, a slow outward transition from interplanetary travel towards cometary source regions and interstellar spaceflight seems conceivable.
That’s a ‘meme’ that Centauri Dreams has been working with for the past seven years, that interstellar flight will grow organically out of the need to extend infrastructure outwards in the Solar System rather than through an interstellar project mounted Apollo-like on its own. The second issue, though, is much more troubling. Sagan and Ostro again:
… altering the trajectories of objects in nearby interplanetary space can introduce perils on timescales much shorter than the average intervals between natural impact catastrophes… Thus, interplanetary collision hazards may act as a kind of sieve, simultaneously requiring civilizations to become spacefaring and to institute stringent controls on the misuse of orbit-engineering technology. These joint constraints may or may not be so severe as to truncate the longevity of spacefaring civilizations below the timescales for civilization-ending impacts themselves. One way or another, interplanetary collisions constitute a unique, exogenous environmental factor in the natural selection of long-lived civilizations.
I’m thinking that Sagan and Ostro had the matter precisely right. Whether through simple error or the calculated decision to use a small NEO as a weapon, the dangers of asteroid deflection for research and mining seem not to merit the risk. I’ll buy the notion that getting to an asteroid with robotic probes or manned missions makes sense as we continue to assess the potential threat they may pose, but let’s reach them without trying to tug them into new trajectories. As Sagan and Ostro noted some time ago, we’re about at the point where we have the technology to alter an asteroid orbit. And as Sagan wrote in Pale Blue Dot (1994), “If we’re not careful, many nations may have these capabilities in the next few decades. What kind of world will we then have made?”
The paper is Baoyin et al., “Capturing Near Earth Objects,” accepted for publication in Research in Astronomy and Astrophysics (Chinese Journal of Astronomy and Astrophysics). Preprint available. The Sagan and Ostro paper is “Cosmic Collisions and the Longevity of Non-Spacefaring Galactic Civilizations,” JPL TRS 1992+, available online. See also Sagan, “Dangers of Asteroid Deflection,” Nature 368, Issue 6471 (1994), p. 501.
SETI and the Use of Tools
It makes perfect sense to me that we usually think of extraterrestrial intelligence in terms of technology. After all, when we listen to the stars for the whisper of a distant signal, we’re saying that SETI is all about finding something that was produced with tools, like a beacon. Or if we extend the thought to science fiction, we might dream of studying alien civilizations through their ruins on long-dead worlds, learning about them by studying what they once built.
After all, this is how we do archaeology, digging up spear-points or the bricks of ziggurats, the things that a culture leaves behind that it built with its tools. But will we always confine the idea of intelligence to the presence of an artifact? Science writer and Astronomy Now editor Keith Cooper examines the question in Dolphins, Aliens, and the Search for Intelligent Life, an incisive new essay for Astrobiology Today, one that offers us a new technology that may prove that intelligence doesn’t necessarily need tools.
CHAT — Cetacean Hearing and Telemetry — is a device built to help humans communicate with dolphins. So far we’ve been able to determine that dolphins do some extremely interesting things from the standpoint of possible language. They can emit whistles and barks, use echo location, and seem to understand a basic syntax, which might flag, for example, the difference between a statement and a question, or differentiate between a past or future tense.
The Nature of a Signal
Some researchers call this a language (whales have many of the same traits), while others call it ‘referential signaling,’ as Cooper explains. Such signaling would involve tagging things with names, but whether or not it indicates a deeply interactive language is another issue entirely. Maybe CHAT can help make the call. It’s a device worn around a diver’s neck, connected to a pair of hydrophones and a simple keyboard that can be used with one hand. The idea is to sidestep the issue of whether dolphin ‘language’ can be translated by setting up the option of a common artificial language that both humans and dolphins could use.
The device is to be tested this year and put into field use in 2012, so we may start to get some results fairly soon. While we await early findings, Cooper talks about Robin Dunbar’s ideas on the social nature of intelligence. Dunbar (University of Oxford) looked at intelligence evolving out of social practice, seeing it as a way for animals not only to survive but prosper in complex social groupings. Let me quote Cooper on this:
These include notions of reciprocal altruism (I scratch your back, you scratch mine), politics (forming sub-groups and coalitions within the larger group) and understanding the emotions of others (empathy, which in turn relies on theory of mind, the ability to be aware of one’s self and others). Looking at it that way, modern social networking on media such as Facebook may just be a symptom of what helped drive us to become intelligent in the first place, many tens of thousands of years ago.
And this takes us back to questions about things like SETI, because we are, after all, talking about how individuals make sense to each other:
Here’s the trick — to be social, you must be communicative. Staying quiet is anti-social. Personal interactions require communication, of some form, and the more complex the interaction, the more complex the communication. So if intelligence and social behavior is linked — and many people agree that it is — then the best place to start looking for intelligence is in animals that like to chat with one another.
Language and Silence
Which circles us back to dolphins, of course, but leave me wondering just what to make of this in a cosmic sense. I grew up being enthusiastic about SETI ever since, as a teenager, I read about Frank Drake’s work at Green Bank, which began in 1960. The idea of researchers scanning the skies for signals seemed so intuitively right that in my naïveté, I assumed we’d track down a confirmed beacon within just a few years.
No such luck, and in the many years since we’ve looked not only at how mind-bogglingly difficult the SETI hunt is at radio frequencies, but how restricting it is to think that an advanced civilization would use radio in its communications in the first place. Now we have to confront the possibility that extraterrestrial intelligence may not be rare at all, but that it may not necessarily lead to tool-building and hence beacons.
Cooper’s essay is just terrific, especially insofar as it gets into Claude Shannon’s 1940s work on the nature of signals, which is so crucial to how we understand data and language (or maybe I should say ‘language as data’). I’ll leave the pleasure of reading Keith’s presentation of Shannon to you because you’ll want to read the whole essay. But it’s worth noting in the SETI context that putting dolphin whistles through Shannon’s information theory demonstrates an internal structure in dolphin communications, while Shannon’s ideas on entropy and language — which focus on language as order and probability — show promising possibilities for dolphin intelligence, although everyone notes the need for more data.
Let’s say, then, that if intelligence is as much about communication as technology, then social behavior may well be the driver on many worlds, where intelligent beings may contemplate the universe without ever developing slide rules or computers or radio transmitters. Perhaps SETI is best considered as SETT — the Search for Extraterrestrial Technology — while intelligent cultures flourish undetected.
Learning more about how species on our own planet use their intelligence, and discovering what sort of linguistic capabilities they actually have, will eventually help us sort out the possibilities. Not everyone agrees that dolphins possess the kind of intellect that could summon up a true language. What a conundrum — we’re not sure whether or not we’re the only ‘intelligent’ species on our own planet. How little we know about intelligence elsewhere in the cosmos!
SETI: Let the Search Continue
Most people think that SETI is worth doing, whether or not they actually believe there are other technological civilizations in the galaxy. Ben Zuckerman, a professor of astronomy at UCLA, is certainly in the skeptics’ camp, thinking there are no technological ETs in the Milky Way, but he’s quoted in this story from QUEST (KQED San Francisco) as calling for more SETI. “Given that the costs are not very high,” says Zuckerman, “why not continue the search?” Zuckerman, who once worked with Carl Sagan in graduate school, no longer thinks we live in a crowded galaxy, but a potential discovery of this magnitude justifies the relatively modest expenditure.
It’s not surprising to find Jill Tarter echoing Zuckerman. The recent funding problems of the Allen Telescope Array have not daunted the woman who more than anyone else has come to represent the search for other intelligent life. And although she believes we may one day come to the ‘extraordinary conclusion’ that we really are alone, the time for drawing that conclusion is hardly near. We have hundreds of billions of stars to choose from in the Milky Way and hundreds of billions of galaxies beyond our own, and in those terms, we’ve barely begun to search.
Image: SETI searcher Jill Tarter. Credit: Sven Klinge.
The KQED story takes note of the new element in SETI research, which has to do with the Kepler mission. With the discovery of more than a thousand planets orbiting stars in its field of view, Kepler may well have found the first true Earth analogues — we’ll know as its data continue to be analyzed. The Kepler findings give us a targeted list of stars that should be high priority for the SETI hunt. “This,” says Kepler team member Dimitar Sasselov, “is where we should be looking for the signals coming from other civilizations.”
Just a month after the hibernation of the Allen Telescope Array due to money problems, the Green Bank radio telescope facility in West Virginia announced its own effort to study 86 of the stars chosen from the Kepler list, scanning an 800 mHz range of frequencies simultaneously (that’s 300 times the range available at Arecibo). Among the 86 stars Green Bank will be studying are 54 candidate systems identified by Kepler as potentially having a planet in the habitable zone. Thus the largest steerable radio telescope in the world picks up on the Kepler work, another case of SETI soldiering on when resources are scarce.
And fortunately, the Allen Telescope Array itself is back in business, thanks to more than $200,000 in donations from some 2400 donors and an infusion of money from the U.S. Air Force, which should keep the project running for the next several months. In the longer term, the ATA needs $2.5 million per year to keep operational, so fund-raising will doubtless become a permanent fixture of the facility’s operations. The SETI Institute’s page supporting a search of the Kepler candidates using the ATA continues to gather donations, a reminder that while SETI may be for now a relatively low-key project, it’s one that generates wide public interest.
Image: A single antenna of the Allen Telescope Array, night. Credit: Allen Telescope Array.
My own views on SETI parallel those of Ben Zuckerman. I doubt intelligent life is widespread in the galaxy, but the whole point of science is to extend our knowledge. By all means, let’s keep SETI in business, and maybe we skeptics will be proven wrong. And just letting the imagination run, it’s fascinating to ponder the world we might live in if one of the Kepler planets turns out to be leaking some kind of artificial radiation. Remember that Kepler is looking out along the Milky Way’s Orion arm, in an area where fewer than one percent of the stars the mission examines are closer than 600 light years. If we were to detect a transmission, it would take 1200 years to receive any return to our potential response. I suspect a detected signal, after revolutionizing our view of ourselves in the cosmos, would probably remain unrepeated and untranslatable, a mystery for our time, an enigma speaking of all we have yet to learn.
Three Views from Outside
The key to a sane life is perspective. Or at least that’s how I feel when I see an image like the famous Apollo 8 shot of a gorgeous blue Earth rising over the barren, cratered Moon. Great images of the kind the space program deals up can change how we see everything — the Apollo 8 image is widely thought to have energized environmental and ecological thinking in its day. We also have a few striking images showing both the Earth and the Moon together. The one I always fall back on is the one below, a barren Moon with a living Earth swimming in black space. It was a departing gift from the Galileo spacecraft as it left on its long journey to Jupiter in 1989.
Image: On its way to Jupiter, the Galileo spacecraft looked back and captured this remarkable view of Earth and the moon. The image was taken from a distance of about 3.9 million miles. The brightly colored Earth contrasts strongly with the moon, which reflects only about a third as much sunlight as Earth. Contrast and color have been computer-enhanced for both objects to improve visibility. Antarctica is just visible through clouds (bottom). Credit: NASA.
Now we have an update of the scene, taken by Juno as it makes its own way to Jupiter. Juno managed the distance from the Earth to the Moon (just over 400,000 kilometers) in less than a day, but it will be another five years and 2,800 million kilometers before journey’s end, where the spacecraft will orbit the giant planet’s poles to study its magnetosphere and probe beneath the clouds. Right now the Juno team is conducting initial checks on spacecraft instruments following the August 5 launch. What we see below was the view from 9.66 million kilometers out.
Image: This image of Earth (on the left) and the moon (on the right) was taken by NASA’s Juno spacecraft on Aug. 26, 2011, when the spacecraft was about 6 million miles (9.66 million kilometers) away. It was taken by the spacecraft’s onboard camera, JunoCam. The solar-powered Juno spacecraft lifted off from Cape Canaveral Air Force Station in Florida on Aug. 5 to begin a five-year journey to Jupiter. Image credit: NASA/JPL-Caltech.
We lack the detail of the Galileo image, of course, but the thrill is still there when you consider what we’re looking at. The Juno team seems no more immune to this than the rest of us:
“This is a remarkable sight people get to see all too rarely,” said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio. “This view of our planet shows how Earth looks from the outside, illustrating a special perspective of our role and place in the universe. We see a humbling yet beautiful view of ourselves.”
Indeed. And while we’re on the subject, let’s not forget another unforgettable view, this one of the Earth and the Moon as seen from the EPOXI spacecraft.
EPOXI (the combined names for the two extended missions of the Deep Impact spacecraft) viewed the Earth/Moon system from almost 50 million kilometers out, the idea being to study how a life-bearing planet would appear to our instruments. Of course, to view a planet at this level of detail from another star system would require technology far beyond what we currently possess. But we’re looking seriously at near-future missions that might be able to pick out an Earth analogue as a single point of light that would change with time as the world rotated. All of this is part of the quest to identify habitable worlds. One day it will happen, but until then, watching that Moon move in front of the Earth is yet another perspective changer, one that leaves this writer a bit amazed no matter how many times he sees it.
Colonizing the Galaxy Using World Ships
The British Interplanetary Society’s Kelvin Long is no stranger to these pages, perhaps best known as the founder and first leader of Project Icarus, but an indefatigable writer on interstellar topics as well. Kelvin’s first book, Deep Space Propulsion: A Roadmap to Interstellar Flight, is scheduled for publication by Springer later this year. Fellow writer Pat Galea has a background in electronic engineering and physics, and has been a professional software engineer since 1993. As well as contributing to the Project Icarus starship design, he is a supporter of Monkey World in the UK, and a staunch advocate for preserving Bletchley Park, home of World War 2 code breaking. Both Long and Galea are Tau Zero practitioners as well. The duo here offer us an overview of a symposium Kelvin recently organized in London that as far as I know was a first: A conference entirely devoted to the breathtaking concept of interstellar colony craft potentially hundreds of kilometers long.
by Kelvin F. Long & Pat Galea, Symposium Chairmen
On the 17th of August 2011, a gathering devoted to the colonisation of space assembled at the headquarters of the British Interplanetary Society (BIS) in London. The society has been the home of visionary research for many years and has never been afraid to allow free thinking speculation on the future of man in space. The topic of conversation for this symposium was the concept of a World Ship. The reference is to a very large vehicle many tens of kilometres in length and having a mass of millions of tonnes, moving at a fraction of a percent of the speed of light and taking from hundreds of years to millennia to complete its journey.
A worldship is self-contained and self-sufficient, carrying a crew that may number hundreds to thousands and might even contain an ocean, all directed towards an interstellar colonisation strategy. Several seminal papers on the topic were published in 1984 by Anthony Martin and Alan Bond. They developed a ‘wet’ World Ship concept 10 km in diameter, nearly 200 km in length, on the order of a peta-kilogram (1015 kg) habitat mass and an equivalent mass in propellant. The biggest of the ‘dry’ World Ship concepts they developed had a diameter of 15-20 km, and was around 220 km in length. The habitat mass was an order of magnitude lower than the wet concept but the propellant mass was similar in magnitude. These are obviously massive vessels and they would travel to the stars with cruise velocities of around 0.5% of the speed of light, taking hundreds of years to reach the nearest stars.
Image: Conference organizer Kelvin Long.
In one of these papers, Martin had this to say:
“The World Ship concept has now evolved to a stage where it needs to be subjected to more searching analysis. The technological and engineering aspects need to be re-examined in more detail… If the World Ship concept survives this scrutiny intact, even if modified in detail, then the fundamental questions raised by the possibility of interstellar travel and colonisation about the apparent absence of extraterrestrial intelligence in the Solar neighbourhood, about the future of mankind, and about its place in the Universe will become more demanding of an answer.”
The recent conference at the BIS included seven presentations discussing the technology, motivations, financing and cultural interactions of communities aboard such a large space vessel. In this article a brief synopsis of the presentations is given, all of which will shortly be submitting for publication in a special issue of the Journal of the British Interplanetary Society (JBIS), further contributing to the important literature of interstellar studies.
The Enzmann Starship
Kelvin Long, a Project Icarus designer, gave a presentation on “The Enzmann Starship: History & Engineering Appraisal,” on behalf of his co-authors Adam Crowl and Richard Obousy. The history of the concept was clarified and it was revealed that a communication with Robert Enzmann had been established. Most remarkable was the fact that Enzmann claims he first thought of the concept in 1949. Every drawing or painting known to exist on the concept was presented to the audience and some of the subtle design changes pointed out. The important role that Rick Sternbach and Don Davis had played in developing the engineering concept, and G. Harry Stine’s in publicising it, was emphasised. Some preliminary engineering calculations were shown on the authors’ understanding of the Enzmann Starship (or Slow Boat): A 30,000-tonne habitat structure with 3 million tonnes Deuterium fuel, travelling a cruise speed of 0.09c (27,000 km/s) on a 60-year journey to the stars. Large scaled versions were also shown as developed by the authors for the symposium, including a 300,000-tonne Slow Ship travelling at a cruise speed of 0.045c (13,500 km/s) on a 150-year journey, and a 3,000,000-tonne World Ship travelling at a cruise speed of 0.014c (4,200 km/s) on a 350-year journey.
The three concepts would start with 200, 2,000 and 20,000 people respectively, but grow by the end of the journey to 2,000, 20,000 and 200,000 people. The mass distribution with the growing population throughout the trip (i.e. ship mass per person) varied from 150 tonnes/person to 15 tonnes/person at the journey’s end, emphasising the need to attempt planetary settlement in some form. Long pointed out that previous NASA space settlement studies had indicated a distribution of around 65 tonnes/person was desirable. The Enzmann Starship was seen as a fascinating idea and the presenter claimed that Robert Enzmann deserved equal recognition with the “other Bobs” in interstellar studies, namely Robert Forward, Robert Bussard and Robert Frisbee.
Image: The October, 1973 issue of Analog featured a gorgeous Rick Sternbach cover of two Enzmann starships to illustrate G. Harry Stine’s article, “A Program for Star Flight.”
Communicating with the Diaspora
Pat Galea, also a Project Icarus designer, gave a presentation on “Communications Between Worldships” or ‘building the Diasporanet’ as the speaker called it. He firstly gave an overview of the Project Daedalus communications systems and described the historical Project Cyclops which was intended for SETI research, but which the Daedalus designers proposed to use for long distance signal reception. Using a 40 m diameter transmitting antenna, with a 1 MW power output, Daedalus could download data to Earth at a rate of 864 kbps (kilobits per second) over a distance of 6 light years. Modern lasers over this distance would have a data rate equivalent to around 10 bps using a 20 W power output, although this could be increased to around 500 kbps using a 1MW power output, but the major advantage of using lasers is that the physical sizes of the transmitting and receiving elements could be much smaller than those used for Radio Frequency signals.
Two network topology configurations were described for World Ships moving outwards radially from a single point (i.e. Earth): multiple connection, in which each World Ship could communicate with Earth and other World Ships directly, and the ‘Star’ topology, in which each World Ship can communicate only with Earth. Galea then described the exciting possibility of using the Sun as a gravitational lens, with a signal relay craft located beyond the minimum ‘focusing’ distance at 550 AU (based on an idea extensively studied by Claudio Maccone). This provides a way of improving the reception of signals from distant World Ships significantly, drastically improving the data rate. To tackle the severe challenge of keeping the relay craft on track (on the order of meters of accuracy), each World Ship would send extremely bright—but very short—’sync pulses’ back to a constellation of Navigational Satellites (NavSats) in orbit around the Sun. By comparing the very slight timing differences of the pulse arrival at each satellite, the NavSats could assist the relay craft in maintaining its track, and thus keeping a lock on the signal being received from the World Ship. As the Earth is acting as a router, passing messages back and forth between the World Ships, this system forms the basis of an interstellar internet, or “DiasporaNet”.
Image: Project Icarus designer Pat Galea.
The Worldship and the Sail
Galea then gave a presentation on behalf of Greg Matloff, who could not make it to the meeting. The presentation was on “World Ships: The Solar-Photon Sail Option.” It was argued that an ideal propulsion option for World Ships is the hyper-thin solar-photon sail, and that this is the only known ultimately feasible interstellar propulsion system that can also be applied for en-route galactic-cosmic ray shields as well as for acceleration and deceleration. The author reviewed three options for sail configurations known as Parachute, Hollow-body and Hoop Sails.
It was argued that although World Ship expeditions may not be likely from the present day Sun using solar-photon sail technology, they would be more feasible as the Sun evolves on and beyond the main sequence. Finally, the author raised the tantalising possibility that future space telescopes may be capable of imaging habitable planets circling near stars which have Solar-photon sail propulsion craft departing the system. The solar-mass type star Pollux at 35 light years was suggested as one location where we could search for evidence of a migration underway. In discussions after the talk, Alan Bond made the comment that using sails for World Ships is prohibitively difficult due to the issues of controlling the large number of oscillations in the sail while in flight. Kelvin Long argued that artificial intelligence technology could take care of that issue, though Bond countered that any smart technology in the sail would add to the mass, making the sail less effective.
Reliability in Deep Space
Andreas Hein, another Project Icarus designer, gave a presentation on “World Ships – Architectures & Feasibility Revisited.” The paper was co-authored with Mikhail Pak, Daniel Pütz, Christian Bühler and Philipp Reiss. The speaker first considered the mean distance to habitable planets, including a 140-light year estimate by Alan Bond, 88-light year distance by Claudio Maccone, and 33-light year distance from Kepler mission data. He considered the definition of a World Ship, and defined three criteria: self-sufficiency (thousands of years), population size (>100,000) and speed (<0.01c). One interesting aspect of the authors’ work was the consideration of reliability and mission success, with modelling performed to address this question. Hein concluded that 99.99% reliability was achievable provided sufficiently large scrap stock was made available for the mission. If the ship had a low reliability, then this could be compensated by sending many such vessels together.
Hein then considered migration push and pull factors. Push factors were defined to be scenarios such as war, genocide and poverty. Pull factors were defined to be education, job opportunities, security, stability, wealth. Finally, potential mission architectures were then considered including a complete trade space of population size, trip time and energy requirements. Hein said that one of the things which would determine the launch of a World Ship was the testing of several prototype vehicles first. He concluded that the mission architecture strongly depended on the habitable planet distance and that self-replication factories and advanced artificial intelligence would likely be requirements for World Ship technology.
The Worldship Rationale
Gerry Webb, a member of the original Project Daedalus Study Group, gave a presentation on “Why World Ships? An Enquiry into the Idea of World Ships and the Nature of Their Sponsoring Cultures.” The speaker first discussed definitions of World Ships and explored the science fiction literature. He said that the 1984 Anthony Martin and Alan Bond definition (see above) was the best one to adopt. He described World Ship concepts such as those presented in Arthur C. Clarke’s novel Rendezvous with Rama. He said it was important that every few decades we discuss the margins of World Ship definitions, looking for show-stoppers to ensure they are not neglected. The evolution of the World Ship concept was described and three reasons for their construction given: (1) saving the human race, (2) inevitable expansion of living space, and (3) actively driven colonization plans. Webb made the important point that humans began to envisage the concept of a World Ship as soon as our knowledge of the physical universe allowed us to do so.
Webb next considered the question of who would sponsor a World Ship, and why they would do it. He said that any society interested in building a World Ship will begin to do so when they have enough materials, energy, information and motivation for doing so. He added: “once the solar system economy is big enough, only the last [motivation] will present a problem for World Ship fulfilment, since ‘starship building man’ is in a very small minority now and may always be”. Threats to long-term human spaceflight prospects were defined to be collision risks, gravity, radiation risks, infections and social disharmony. He considered the factors that make humans what they are, and defined us as Genes (G), Culture (C) and Ideology (I) which are the hardware, operating system and program respectively. He said that all three of these elements would be of equal importance in attaining a human success in World Ship building, and hence our survival and expansion into the galaxy.
An important point made by Webb was that it had been found that approximately 1% of every nation on earth was made up of so-called psychologically difficult types, meaning manic depressives or those suffering from mental disease. This remarkable constancy, it was claimed, may have contributed to human cultural and ideological advances. In discussions, Kelvin Long pointed to the Arthur C. Clarke story The City & the Stars, which had a small instability element to the population. Webb argued that the government of a World Ship was very important in order to maintain stability. He referred to the Aristotelian organization of states in order of decreased stability as Tyranny (monarchy or totalitarian), Oligarchy (aristocracy or elitist) and Democracy (polity or republican). Those sponsoring a World Ship would be natural expansionists—ark builders—and the pressures to do so would be government funded programs, private funded, or internal pressures such as victimization or resource depletion. Finally, he said that given a big enough economy, World Ships would be inevitable, and each ship may be very different, based on different beliefs and ideologies. Darwinian natural selection would ensure that only the fittest would reach the destination stars. The others would simply not make it there. He ended with a cautionary note relating to the Fermi Paradox which may become more topical by the time that a World Ship is built and said that if alien World Ships exist, they may not be sympathetic to us.
Estimating a Launch Date
Stephen Ashworth gave a presentation on “A Development Roadmap for the World Ships.” The speaker raised the possibility that we may become extinct before we have a chance to build a World Ship. Ashworth thought that the construction of free-orbiting space colonies would be prototypes for World Ship living quarters. He discussed current propulsion technology such as that used by the DAWN spacecraft travelling at around 30 km/s, and speculated on future propulsion systems.
Ashworth strongly disagreed with the picture painted by some of an ‘Independence Day’ scenario where colonies hop from one world to the next to extract vital resources. He displayed graphs illustrating the sum of journey and exploration time against habitability time (the duration upon which we could inhabit artificial space colonies for a continuing duration). The point at which the figures cross over was said to be an estimate of the time at which we could likely launch the first World Ship. 2357 was estimated initially assuming progress in both life support and propulsion. However, if progress in propulsion is more rapid, Ashworth believes the first World Ship launch date could be brought forward to a much earlier date. If life support technologies progress but propulsion does not, then the launch date would be pushed back to around 2450. Alternatively, if progress in life support technologies and propulsion declined then the two curves may never cross each other, meaning we may never launch a World Ship.
Ashworth concluded by saying that much attention was being placed on finding an Earth-analogue planet, and although he thought this was a worthwhile pursuit of scientific study and recreation, he did not think it was the object of resource extraction or colonisation. In all likelihood, he said, humans would prefer to live in artificial orbiting space colonies rather than living on another planet. This view was not shared by all present. In particular Martyn Fogg (of terraforming fame) said that he would like to see the habitable planets and this would be a reason for making the journey. Ashworth ended by saying that World Ships would be a logical end point to the colonisation of the solar system — they are inevitable.
The Economics of Interstellar Growth
Finally, Frederik Ceyssens gave a presentation titled “On the Financing of World Ships & Other Gigascale Space Projects.” His co-authors were Maarten Driesen and Kristof Wouters. Ceyssens discussed the new age of discovery, in which astronomers are finding hundreds of exoplanets constantly. He argued that there will be more interest in exploring and settling on another habitable world. Such settlements may have greater potential for grand scale colonisation than a colony in our own solar system and also provide long-term survival and knowledge-generation benefits. The question for him was whether this interest is sufficiently strong to attract funding.
Ceyssens defined some of the challenges facing current space exploration, namely low-cost access to space, very high specific impulse propulsion, high reliability and lifetime for equipment, and creation of life support systems. His conclusion was that a World Ship would be an ultra long-term project and at high cost. He said that a World Ship would be equivalent to a ‘beefed up’ megaproject such as Project Apollo, megaprojects being defined as involving a steep threshold unsurpassable by normal economic or scientific development. As well as Project Apollo ($100bn) he discussed other megaprojects including the Manhattan Project ($22bn), ITER ($20bn) and the construction of either an interstellar probe ($1,000bn) or a World Ship ($10,000bn). He considered projections for World Ship investments assuming set annual growth figures.
Ceyssens’ proposal for achieving the eventual launch of a World Ship was the formation of a ‘Fourth Millennium Fund’ which he argued would be transparent, have global outreach, be lean with a low cost structure and have a single well defined goal, such as finding a second home for humanity. He was looking for people to invest today and to commit to such long term investments to ensure that a World Ship could be built in the future, once we could afford it. It is worth noting that Alan Bond made a comment that, in his opinion, money as we know it in the future will not be the economic system by which things are constructed and resources are allocated.
A Fallback Plan for Earth
During the subsequent discussions many competing views emerged from the attendees relating to World Ships. One of these was the view that before any World Ship would depart it would first identify a habitable planet to head towards. However, several attendees thought that the advanced crew (so called Starship Man) would no longer be interested in settling another planet but would instead be content to live in artificial structures in orbit.
The question of when such a mission would be launched was also debated. Some saw it as an inevitable gradual process of solar system colonisation placing it many centuries into the future, whilst others thought that circumstances on Earth (e.g. catastrophe, war, famine) may give rise to the construction and launch of such a mission much earlier than people think. This would also determine the stability of the crew aboard the World Ship. A mission planned centuries in advance with great care would have a well organised community on board paying attention to population control, policing and resource usage. But a World Ship constructed in a hurry may have less detail in the planning, with the result that only a dictatorial style rule on board the vessel would be capable of maintaining social stability. These sociological factors would likely have a significant impact on the success or failure of such a mission.
As we consider the future prospects of mankind on Earth and in space, it is important that we keep our options open. From the perspective of today’s society, with a large population, poor resource distribution, and in financial crisis, the prospects for building a World Ship some day seem at first sight to be pure science fiction. However, there is nothing in the laws of physics or in the many text books on engineering that suggest a World Ship is impossible to build. As indicated by Alan Bond during the discussions, a future society, perhaps in a better position than we are in today and with a more positive outlook on the Universe, may look upon such an enterprise as an equivalent undertaking to Project Apollo in the 1960s. Given the potential threats — internal and external — that humanity may face in the future, it is important we keep our options open and continue to strive for expansion into space. Designing World Ships is a lot of fun in the practice of extreme aerospace engineering, but it is also a possible fall-back plan should the future turn out to be bleak for humanity on Earth.
Image: Kelvin Long (left) and Alan Bond at the conference.
On a final note, we have to accept that if humans can conceive of a World Ship, then so could an extraterrestrial and they may be out there now star hopping, perhaps on their way here. Alan Bond pointed out that a nuclear pulse engine would be detectable from large interstellar distances and would appear to be a double-ping milli-second pulsar running down on the timescale of decades as it moves away from us. He said that our machines will colonize the stars before us, and so might the machines of another race. Perhaps we should be more concerned if the starships were coming towards us.
It is worth ending this article on a cautionary note from Arthur C. Clarke: “I can never look now at the Milky Way without wondering from which of those banked clouds of stars the emissaries are coming.”
The two original papers referenced in this article by Anthony Martin and Alan Bond are “World Ships – Concept, Cause, Cost, Construction and Colonisation” and “World Ships – An Assessment of the Engineering Feasibility,” both published in JBIS, volume 37, number 8, June 1984. Kelvin Long has also published a separate conference report on the Project Icarus site.
Entering the Age of Sail
I see that the new agenda for the 100 Year Starship Study symposium has now been posted. The meeting will be held in Orlando in about a month, set up along a number of parallel tracks from interstellar destinations to propulsion options and habitats, a wide-ranging set of sessions that will allow many in the far-flung interstellar community to exchange ideas in person for the first time. DARPA’s intention is to spur research and select an organization that will sustain and develop interstellar ideas over the next century, an exciting long-term prospect indeed.
That interstellar flight demands long-term thinking should be obvious given the state of propulsion research today. Over the last sixty years, numerous ideas on how to drive a vehicle to a substantial percentage of the speed of light have been advanced, but almost all of these remain no more than concepts in journals. We’re not remotely at the stage where we can choose a single option as the likely propulsion choice for development. Rather, we’re theorizing and experimenting and seeing where many different strands of thinking lead, all of which takes me to the solar sail.
Jim Essig was kind enough to pass along a recent story in Science News dealing with current experimentation and planning on solar sail ideas. Here we’re dealing with a technology that, unlike almost all the other interstellar options, has actually flown, even if we’re still in the preliminary phases of evaluating the technology’s performance. One day it may be that we’ll push enormous sails with laser beams or microwaves, but for now we’re talking about small attempts to measure the effect of momentum transfer by solar photons to push a spacecraft.
Image: A close-up of the fully deployed IKAROS sail. Credit: JAXA.
The Japanese success with the IKAROS sail has been marvelous to watch as the 20-meter sail became operational in interplanetary space, demonstrating an innovative liquid crystal technology that allowed mission scientists to change the sail’s reflectivity and affect its course. Bear in mind that IKAROS is to be the first of a family of Japanese sails, the next model being 50-meters across and intended for launch to Jupiter and the asteroids. That mission will focus on propulsion systems that combine the solar sail with an ion drive for interplanetary journeys.
We’ve talked extensively in these pages about IKAROS as well as NASA’s NanoSail-D, the latter whimsically called LunchSat because the budget-strapped team could only find time to work on it during lunch. Nonetheless, the doughty engineers under Dean Alhorn built two 3-meter sails that fit into a CubeSat, attempting to launch the first without success because of the failure of the Falcon 1 rocket that would have taken it into space. The second was launched last November, went silent for weeks, and suddenly deployed and reported in for duty. Alhorn has now set his sights on a larger sail to follow on to NanoSail-D, which will re-enter the atmosphere within months.
The NASA effort had downsized since the days when the agency was testing two 20-meter x 20-meter solar sails at a research facility in Ohio [although see Jack Crawford’s comment below], but the fact that NanoSail-D could become operational is a testament to the enthusiasm of scientists working the mission. And the new sail possibility is a 38-meter x 38-meter sail demonstrator, as discussed in this news release from the Office of the Chief Technologist.
The Science News story is well worth your time for its encapsuled analysis of where we are in solar sail development. We now look toward the Planetary Society, where Lou Friedman brings his own extensive sail experience to the building of three potential designs. From the story:
Closest in concept to the original grand dreams about solar sailing, yet freighted with the memory of a recent failure, is the LightSail project of the Planetary Society. Friedman, its architect, has seen pretty much everything in the world of solar sailing; he worked on the original Halley proposal in the 1970s and spearheaded the society’s drive to fly a privately funded sail in the early 2000s. That effort, paid for mainly by an entertainment company led by Carl Sagan’s widow, ended with a splash in 2005 when the Russian rocket it was supposed to ride from a nuclear submarine failed to reach orbit.
After licking his wounds, Friedman decided to work with NanoSail-D in its initial stages. That restored his enthusiasm and inspired LightSail. “We got so interested in the design that we said we’ll go further: We’ll instrument the craft and build in attitude control and a telemetry system,” says Friedman. Thanks to CubeSats, the sail could be built for less money than the society’s last, failed attempt.
Image: Chris Biddy (left) and Lou Friedman at Stellar Exploration (San Luis Obispo, CA) for the first full-scale deployment test of the sail on LightSail-1. Credit: The Planetary Society Credit: The Planetary Society.
Like Alhorn’s NASA team, the Planetary Society is building two sails in case something goes wrong, and envisions future versions that will not only achieve higher Earth orbit but travel to the L1 Lagrangian point between the Earth and the Sun. Other sail projects to watch with interest include a consortium from the University of Surrey and aerospace firm Astrium, an aerospace subsidiary of the European Aeronautic Defence and Space Company (EADS) that is building a 5-meter sail for CubeSat deployment for launch some time in 2012. The same team is studying sails as a way to deorbit satellites, removing space debris that poses a collision hazard in orbit — this is also part of the thinking behind the NanoSail-D concept.
And we’re still not through. The German space agency DLR and the European Space Agency are working on a series of solar sails called Gossamer that would experiment with larger sails as technology demonstrators of increasing size and complexity, while engineers at the University of Illinois at Urbana-Champaign are studying new deployment methods that involve spinning deployment of sail blades that could one day lead to a spinning sail with rotating blades as large as 10 kilometers long. As Science News points out, what will move the solar sail idea forward is not just this early experimentation, but the follow-on missions that target specific tasks that are optimized for sails and defy other propulsion techniques. In such ways does a promisng space technology begin to get the shakeout in space it needs to mature.
Image: ESA & DLR Project Gossamer in orbit. Credit: DLR.
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