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Interstellar Flight: Equations and Art

Les Johnson (MSFC) always says that the coolest job title he ever had in his long career at NASA was Manager of Interstellar Propulsion Research. Think about it — if going to the stars is your passion and you have a title like that, you must feel that you have really arrived. These days he goes by the more prosaic title of Deputy Manager for the Advanced Concepts Office at Marshall Space Flight Center in Huntsville, but as the recent interstellar workshop in Oak Ridge demonstrated, he’s also ranging widely on his own as conference organizer, author and science fiction aficionado. His presentation in Oak Ridge was designed to jump start the conference with a survey of the problems of interstellar flight and the long list of possible propulsion solutions.

The Interstellar Conundrum

The problems are clear enough. Think of the distance between the Earth and the Sun (about 150 million kilometers). That’s 1 astronomical unit (AU). Shrink that distance to one foot and imagine the Solar System, with Neptune 30 feet out and so on. On that scale, the distance to the Alpha Centauri system is 47 miles. Moving at 17 km/sec, Voyager 1 would take 74,000 years to make the Centauri journey (if it were pointed in that direction in the first place, which it is not). Les was part of the Interstellar Probe Science and Technology Definition Team that aimed at designing a spacecraft that could reach the heliopause, and at this point in our technological evolution (this was back in the 1990s), it was clear that three propulsion options were possible: A chemical rocket with gravitational slingshots at both the Sun and Jupiter, solar sails, or nuclear electric.

Let’s pause on the latter. Electric propulsion, which uses electrical energy to heat and eject the propellant, offers much lower thrust levels than chemical propulsion, but it is ten times more efficient per pound of fuel. A mission to the outer system would require a nuclear power source operating at high power, but the technology is workable and in Les’ opinion could deliver a mission to 200 AU within 20 years of launch. Solar sail options are likewise no longer theoretical, and Les pointed out that NASA has selected L’Garde to work on a sail a bit less than 80 meters to the side that is to become the agency’s first deep space sail experiment in about three years.

From nuclear pulse propulsion (Project Orion, the size of an aircraft carrier, would present serious problems in terms of in-space assembly) to nuclear fusion and antimatter-catalyzed fusion, a variety of nuclear concepts have been considered, including the British Interplanetary Society’s Project Daedalus and the ongoing Project Icarus studies. Antimatter remains an elusive goal. We would need antimatter production of just kilograms per year to drive a true interstellar mission (compare this to tens of thousands of tons of helium-3 and other fuels needed for a Daedalus), but our current antimatter production is mere nanograms per year.

The Q&A session that followed Les’ talk brought a response to his contention that fission was not practicable for interstellar travel, noting that staged fission rockets might be able to reach 2 percent of lightspeed. If so, that does change the picture somewhat, and if anyone has a reference to a paper on staged fission concepts, I’d like to read more about this. Another interesting note: Les’ book Going Interstellar, edited with science fiction writer Jack McDevitt, is coming out from Baen some time in 2012. This is a collection of essays and fiction, and it was great to hear that the publisher intends to bring out a teacher’s guide to get these ideas to high school students. We need to energize that next generation.

Pushing into the Artistic Frontier

C Bangs is a Brooklyn-based artist whose work draws on a vision of man’s future in space. I use the term ‘vision’ with care, because I find her work laden with mythic echoes of our species’ past even as it points to a cosmic destiny that we seem impelled by our nature to strive for. I’ll add this: My own background as a medievalist left me with a fascination for illuminated manuscripts like the Lindisfarne Gospels and the Icelandic Flateyjarbók. Some of C’s work reminds me of ancient manuscript designs even as it draws on cutting-edge physics and astronomy, subjects she has illustrated so well in her collaboration with her husband Greg Matloff. If you page through a book like Solar Sails or Paradise Regained, you’ll see how her work re-states the scientific themes with archetypal resonances that take the reader into the realm of the transcendent.

Image: Green Man & NGC #4414. Credit: C Bangs.

The Paradise Regained book is particularly to the point here, because as C told the audience in Oak Ridge, she has long been fascinated with the Gaia Hypothesis, the concept that the Earth as a whole is a cooperative system that maintains conditions for its own survival. You can wed this deep interest in interlocking systems with a love of landscape that was surely nurtured by trips to Puerto Rico, where her father was teaching. One of these trips led to a tour of the great Arecibo dish, an experience that was both majestic and transformative. From then on, cosmology would weave into mythology as the basis for her vision. Her work for NASA includes a holographic coating technology that could enable 3-D images to accompany deep space missions (a set of her holographic work is housed at Marshall Space Flight Center).

What struck me as C showed images of her work in Oak Ridge was the sense of optimism they contained. If she explores human consciousness through archetypes, she also insists on a positive response to the cosmos and an engagement with cutting-edge ideas. It’s no surprise that interstellar studies champion Robert Forward was a key figure in securing her early funding from NASA, and her continuing work with Greg has ensured that she keeps current with the interstellar community. Optimism may grow naturally out of that engagement, the idea being that without a frontier to explore, the problems of this planet can seem overwhelming, leading to a cynical, defeatist kind of art that is worlds away from what C expresses. Our problems are indeed huge, but space offers solutions to our resource crisis and feeds our need for exploration, the latter a deep-seated drive so well captured in C’s eloquent imaginings.

Image: Leopard Ceremony & Eagle Nebula. Credit: C Bangs.

Project Icarus: Pushing Designs to the Edge

People sometimes say that Project Icarus has a strange name, given that Icarus was a mythological figure who flew too close to the Sun and thus met his doom. But Icarus is also a logical name for the project that would follow up the 1970s-era Project Daedalus, which had been the first detailed design study of a starship ever made. After all, Icarus was the son of Daedalus, and as Richard Obousy pointed out in his presentation in Oak Ridge, the idea is that Icarus was a pioneer who pushed his technology to its limits to reveal its hidden flaws. Project Icarus aspires to do the same, to push a fusion design hard to uncover hidden problems, and determine just how much we have advanced since the heady days of Project Daedalus.

Now Richard Obousy is as engaging a proponent of interstellar flight as one could meet, and we enjoyed a lengthy dinner conversation after the day’s sessions were over. Every now and then I talk in these pages about teaching tools, the kind of comparisons that help us understand things like interstellar distances. Rich had one for me — Look at a map of the United States and imagine that the Earth is in New York City, while the Alpha Centauri stars are in Los Angeles. With that scale in mind, realize that our Voyagers, now entering the heliopause, would be roughly 1 mile along the route to LA. What we need to do, as Rich told the audience during his talk, is to increase velocity by a factor of about a thousand, to make missions consistent with human lifespans. Icarus chooses fusion as the best way to liberate the energies needed for that.

Image: Project Icarus arriving at a destination system. Credit: Adrian Mann.

The Project Icarus playbook is a thing to behold, with twenty different research areas under active investigation, everything from primary propulsion and fuel to power systems, communications, computing, vehicle assembly, risk and repair. Each of these modules has a lead and each lead has a team dedicated to solving the challenges of his or her subject. The purpose is not to build a starship — we’re a bit ahead of the curve for that — but to motivate a new generation of scientists to become involved in interstellar studies, to generate interest in precursor missions, to explore credible design concepts and assess the maturity of fusion.

The 100 Year Starship Study DARPA has funded will be making an award of $500,000 to the team it chooses to advance interstellar ideas in coming years — both the Icarus team (operating as Icarus Interstellar) and the Tau Zero Foundation have submitted proposals, along with a number of other organizations. We won’t know who wins the grant for a few months yet, but ponder the overall ideas. As Obousy told the audience in Oak Ridge, the average lifespan of a company in the United States is 13 years. What DARPA wants to do is provide seed money for an organization that will last for centuries. That in itself is perhaps a bigger challenge than building a starship. It involves an attempt to find the next Google, the next Apple, and to so craft the organization that it can survive economic ups and downs and changes in intellectual fashion.

Can it be done? The DARPA award-winner will make the effort, one that Centauri Dreams heartily applauds because it requires long-term thinking pushed to its limits, and shrewd marshaling of existing resources. Interstellar studies is an exciting place to be. We’ll talk on Monday about another exciting concept called ‘shell worlds’ that I learned about in Oak Ridge, and discover why little Ceres may one day be the richest world in the Solar System.

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Comments on this entry are closed.

  • Astronist December 2, 2011, 11:24

    Hi, Paul. I’d suggest being a bit careful with phrases such as “a cosmic destiny that we seem impelled by our nature to strive for”, even when evaluating works of art. Firstly, there is no guarantee that a species or civilisation at any one level of complexity or geographical range will evolve to a level of greater complexity or range; it might equally well decline or become extinct, as has often happened in the past. When discussing interstellar travel, we must at the same time be very aware of the threats of resource exhaustion, environmental decline, political or economic collapse which could terminate our creative abilities before we ever reach that stage. In fact, I’d suggest that every starship study needs to include at least a sketch of how we achieve the sustainable industrial growth necessary to get to the point where we’re ready to start building the ship. Boring groundwork, but indispensable. And secondly, while a few of us do very much feel impelled by our nature to get out there and explore, many do not, and are no less human for wanting to stay at home!

    Thanks for the great report on Les Johnson’s workshop.

    Stephen
    Oxford, UK

  • Jamie Chastain December 2, 2011, 13:05

    The works pictured in your article seem akin to Kandinsky, no?

  • Duncan Ivry December 2, 2011, 13:09

    “What DARPA wants to do is provide seed money for an organization that will last for centuries. … It involves an attempt to find the next Google, the next Apple …”

    This is an interesting detail, I think. There have been many attempts, e.g. in the science of economics, to make such forecasts. All these attempts failed. I think, just the current worldwide economic and political crisis is a clear hint — and not the first one — at the “un-forcastability” of these phenomena and not being able to make reliable plannings based on this.

    Since my days at university I had the question *why* it’s possible or not to forecast certain economic phenomena, and I did some research when being at university and afterwards. The authors in the area of economics don’t tell anything substantial. In the area of the theory of science there are some useful thoughts (but it’s impossible to expand on this here, sorry).

    Based on what I know until now, my bottom line would be the following:
    If finding the next Google and the next Apple (speaking metaphorically) is a precondition for the success of the 100 Year Starship Study — which I don’t know (and I hope it’s not) –, then I would be rather pessimistic; it would be better if “we” manage to circumvent this obstacle at the outset and learn to live with the uncertainty.

  • Istvan December 2, 2011, 16:17

    I’m no fan of antimatter propulsion, as I generally think it rather too far-future to be concerned with at present, but with the recent discovery of an antimatter reservoir associated with the Van Allen belts, I’m unwilling to use our miniscule artificial production as the reasoning to pooh-pooh the prospect out of hand anymore.

    Would anyone happen to know if there have been any attempts to quantify the orbital antiproton reservoir discovered by the Pamela instrument aboard Resurs-DK1? I presume we’re dealing with a torus, but of what dimensions and density I’ve seen no data whatsoever.

  • Paul Gilster December 2, 2011, 18:45

    Astronist writes:

    I’d suggest being a bit careful with phrases such as “a cosmic destiny that we seem impelled by our nature to strive for”, even when evaluating works of art.

    I don’t disagree with much of what you say, Stephen, and yes, there are all kinds of things that could prevent our species from ever having an interstellar future. But my point is that the urge to explore seems to be wired into us, whether we can succeed with our aspirations or not. And while there are many people who don’t necessarily want to get out there and explore, there always seem to be a sufficient minority who do take these steps. I should add that I am not much of an exploring type myself, at least when it comes to dangerous journeys ;-)

  • Eniac December 2, 2011, 21:52

    Paul,

    I do not know about “staged” fission rockets, but I would like to point out this work:

    http://www.rbsp.info/rbs/RbS/PDF/aiaa05.pdf

    Which seems to indicate that fission could be perfectly suitable and even comparable with fusion for interstellar travel. In particular, from the abstract:

    The highly directional fission fragment exhaust can produce a specific impulse of one million seconds resulting in burnout velocities several thousand times those attainable today.

    “several thousand times” seems to be just what the doctor ordered….

  • Tero Niemi December 2, 2011, 22:04

    > Firstly, there is no guarantee that a species or civilisation at any one level of complexity or geographical range will evolve to a level of greater complexity or range; […]

    But we can dream?
    Can I say, perhaps even… centauri-dream?

  • James December 2, 2011, 23:34

    Paul, when can we see the youtube video of the workshop?

  • Paul Gilster December 3, 2011, 9:42

    James, I don’t know the schedule on getting the videos up on YouTube, but I’ll make sure to announce it here when they are available.

  • Paul Gilster December 3, 2011, 9:46

    Eniac writes:

    I do not know about “staged” fission rockets, but I would like to point out this work:

    http://www.rbsp.info/rbs/RbS/PDF/aiaa05.pdf

    Which seems to indicate that fission could be perfectly suitable and even comparable with fusion for interstellar travel.

    Interesting! I want to dig into this a bit more — thanks for the reference.

  • Paul Gilster December 3, 2011, 9:48

    Jamie Chastain writes:

    The works pictured in your article seem akin to Kandinsky, no?

    I took a whirlwind Kandinsky tour online and I see what you’re talking about — I wonder if C considers Kandinsky an influence.

  • Eniac December 3, 2011, 10:14

    In principle, fission fuel contains enough energy to propel the fragments out the rocket at almost 0.12 c (I am not sure why the authors claim higher velocities, I used 0.5 mv^2 = 0.007 mc^2). Thus, the achievable burnout velocity of a perfect fission fragment rocket ought to reach all the way up to 0.3-0.5 c, which is not bad at all.

    The dusty plasma rocket from the reference appears to operate not too far from perfect, with the various losses all in the range where you have at least a substantial fraction of the total left. However, as far as I know it is still a purely theoretical device. An actual device would obviously be very messy.

  • Brett Bellmore December 3, 2011, 11:01

    “the idea is that Icarus was a pioneer who pushed his technology to its limits to reveal its hidden flaws.”

    I know what you’re suggesting, but if you go back to the original legend, Icarus was an immature child who, in his excitement, exceeded design constraints he’d been specifically warned of.

  • Adam Crowl December 3, 2011, 18:18

    Hi Paul
    Seems Eniac jumped for the same reference I did. Fission-fragment rockets, which Robert Sheldon has proposed a design variant of using dusty plasma, do indeed have the ability to reach very high exhaust velocities. One problem they have, which Sheldon touches on, is the need for the fissioning material to be close enough together so a chain reaction can be sustained, but far enough apart that the fission fragments can escape without transferring heat to the reaction chamber. Not an easy task. Sheldon’s innovation is to suspend the fission fuel as a cloud of charged dust within a strong magnetic field.

    Robert Frisbee has discussed Fission-Fragment Rockets as roughly the equivalent of pulsed fusion rockets for low speed interstellar missions – their Isps are roughly similar ~1 million seconds. Fusion, in theory, can produce higher exhaust velocities, about x2-x3, but the requisite burn-up fractions of ~100% are very hard to do for fusion, yet rather easier for fission. Thus the two end up being similar.

    Another alternative is Bob Zubrin’s Nuclear SaltWater Rocket (NSWR) which John Cramer wrote up years ago for “Analog” (Mid-Dec 1992)…

    Nuke Your Way to the Stars

    …the most extreme version of which promised an Isp of ~480,000 s, sufficient for the 0.02c mission Paul reports.

  • Eniac December 4, 2011, 1:11

    Adam summarizes the technology very well. Salt water rockets would be about an order of magnitude less efficient than fission fragment rockets, because of the water that constitutes an inert propellant and leads to the reduced exhaust velocity. On the other hand, they seem to be easier to develop, so perhaps ought to be tackled first.

    Maybe a hybrid could be devised, where instead of saltwater pure fuel is expelled in a convergent set of dust streams to react just outside a magnetic nozzle? Perhaps not, because of the lack of a moderator. Perhaps much less moderator would be needed if were mixed in as a solid with the streams? Perhaps there is a nuclear fuel that does not require a moderator? Plutonium can sustain a fast neutron chain reaction, or not?

    Anyway, given that fission is apparently just as promising in terms of performance as fusion, and much easier to achieve, perhaps the Icarus team ought to consider moving towards it.

  • Eniac December 4, 2011, 1:25

    It turns out that a moderator is not really needed with sufficiently concentrated fuel, so maybe a “dusty stream” rocket could indeed be built. It could have a better chance at being efficient than the contained dusty plasma proposed by Sheldon, because there would be no losses to the containment field and walls. It would also have a much higher Isp than the NSWR proposed by Zubrin, because there would be no inert propellant/moderator present.

    http://en.wikipedia.org/wiki/Fast-neutron_reactor

  • Interstellar Bill December 5, 2011, 3:45

    It’s all going to be about stepping-stones:

    Fission’s ignition temp is far lower than that of He3,
    so it should be the first to be done large-scale.
    (By that I mean done by a space-based civilization.)

    The high reliability required for decades-long missions
    can only be developed after long gestation,
    the technology proving itself on manned missions,
    particularly to the outer planets,
    before such valuable machines would be left unattended
    and expected to light off 50 years later.

    Since a hyper-telescope is far cheaper than a starship,
    we’ll know if Alpha Centauri is even worth going to.
    If it is, then a flyby probe would know where to go.

    Just like fission before fusion,
    a flyby will naturally precede a rendezvous,
    in spite of its lower value,
    because all its computer has to do is take data,
    whereas carrying out a complex long-term rendezvous mission
    overseeing multiple landers and orbiters —
    Lotza luk pulling that off the very first time.

    No, surely there’ll first be many, many Kuiper-Belt missions
    to perfect the art of autonomous unmanned exploration.

    Likewise, only an unmanned rendezvous mission
    could report back on what spacers will prize most —
    asteroidal resources, extremely difficult to ‘scope out’ from here.

    Manned missions will for sure be one-way, upon arrival
    absolutely requiring vital portions of the periodic table.

    There will have to be enough people to build a receiver laser,
    so that immigrants can sail there in large numbers at 0.5c.

  • Brett Bellmore December 5, 2011, 8:38

    Of course, when you’re using pure fissile materials as fuel, the problem isn’t achieving criticality in the engine. It’s avoiding it in the fuel tank. This makes reaching high ISPs and high mass ratios at the same time rather complicated for these sorts of engines. How do you build a rocket that’s 95% U235?

    I suppose by using space and geometry to prevent a critical mass, rather than shielding. Perhaps the fuel could trail behind the rocket in the form of wires, reeled in as needed. Or be distributed about the craft as standing spines, or a thin sphere, supported by electrostatic charge. But it seems clear to me that you’re not going to compactly store fissile fuel without a considerable weight of shielding.

    Which, if you’re stuck with, you might as well send out the exhaust.

    For a long mission, I suppose you might breed fuel en route, and compactly store fertile fuel.

  • Greg December 5, 2011, 9:45

    Giving it some thought, it may be possible to use a neutron generator to keep the reaction in a fission fragment rocket going, overcoming the need for a chain reaction.

  • jkittlejr December 5, 2011, 13:35

    Dear ” i-Bill ”
    lI like your thinking. I would certainly would like to see us move toward the icy bodies of the Kiuiper belt as well as build on Ceres first. I think this may have a practical stepping stone, See note about about Bagged icy bodies that is attached to the discussion of shell worlds. we could start with a bagged asteroid about 1 km in diameter.

  • Greg December 5, 2011, 23:42

    Brett, a solution maybe to have the nuclear fuel separated by a low melting moderator, a form of hydrocarbon, possible plastics which are good at capturing/stopping neutrons, that can either sublimate or vaporize at higher temperatures making it a good way to store the nuclear materials until its needed.

  • Eniac December 5, 2011, 23:56

    Just like fission before fusion,
    a flyby will naturally precede a rendezvous,
    in spite of its lower value,
    because all its computer has to do is take data,

    This one I am not sure about. A few minutes for observing vs. many years seems much worse than just “lower value”. Even if all the plans for orbiters and landers fail or are not attempted to begin with, it would still be MUCH better to have years worth of data for the computer to take, instead of minutes. It seems well worth the cost: double the travel time. Although, if it is 100 vs. 50 years, maybe it isn’t?

  • Interstellar Bill December 6, 2011, 13:08

    Eniac (I remember seeing an Eniac on TV in 1952)

    A fly-by would cost only a few percent of a rendezvous
    and be so much easier that it would be done far sooner.

    Its few minutes of data would tell us
    if the system is worth going to at all.
    For example, if even the biggest hyper-scopes
    find no planets around Proxima or Alpha,
    then a flyby would be sent to look for asteroids.
    If it finds nothing, then a rendezvous would be worthless,
    and our sights would turn to Epsilon Eridani.

  • Eniac December 6, 2011, 23:25

    A fly-by would cost only a few percent of a rendezvous
    and be so much easier that it would be done far sooner.

    That depends on the speed you go at. It is a few percent only at a particular large mass ratio. A better way to look at it is that anywhere you can go for a flyby you can also go for a stop in double the time, with the same fuel. You simply save half of your delta-v for deceleration. If you account for the time spent accelerating, it is indeed less than double.

    So, at a given budget, you trade travel time for observation time, but the observation time difference is disproportionally larger, by orders of magnitude.

    I would also submit that the flyby may not be easier, as you claim. A relativistic ship is not very maneuverable, and course corrections may indeed be near impossible. With a rendezvous, if after deceleration you are not quite in the right place, you can use remaining fuel to make corrections, like on the golf course. With a flyby, you have only one shot. What goes in the hole easier, a golf ball, or a bullet?

  • spaceman December 7, 2011, 5:31

    Unlike fusion, we already have now had several decades of experience operating this high energy density form of energy release. Fission-rockets would seem like the most promising near-term means for efficiently expanding our presence in space. The biggest obstacle to this approach is obviously the threat of a launch failure dispersal of the fissile material into earth’s atmosphere. Perhaps this potential problem of accidental atmospheric contamination could be solved by obtaining the fissile material from another solar system body and building the rocket entirely in space.

  • spaceman December 7, 2011, 5:32

    I still think interstellar travel, if we attain it someday, will have come about more from a sense of adventure and exploratory urge until the far future when the Sun starts to fail. The reason why I think is so is that the endless growth economic model is already reaching its limits here on earth and we will, as a species, either transition away from this model or suffer inevitable demise due to ecological collapse. But it is precisely this model that some say will EVENTUALLY propel us into space to look for new resources to fuel our growth model. But it is far from clear that the growth model will propel humanity into space before propelling us toward ecological collapse. Yet if the growth model is forsaken, then the impetus that many posit it may provide for expansion to meet our extractive needs will cease to exist. What motivation to expand will remain when and if the growth model fades into history? In a hypothetical post-growth world, will sheer curiosity and/or the aforementioned sense of adventure suffice to mobilize large groups of people to seriously participate in bringing about a spacefaring civilization long after the scramble for resources disappears?

    I have thus identified a paradox of sorts. I will call it the Growth-Expansion Paradox of Space Colonization.

    In rough form it is as follows:

    If we do not discard the endless growth model, we will face ecological collapse.

    If we do discard the endless growth model; however, we will be removing what some say may eventually be the driving force behind our colonization of space.

    Thus, if colonization of space is to take place it must arise from aesthetic and/or adventure-based motive, as it is highly unlikely given current trends that the endless growth model will propel us into space before propelling us toward ecological collapse.

    Paul, my friend, what do you think of these ideas?

  • Paul Gilster December 7, 2011, 9:49

    spaceman writes:

    If we do not discard the endless growth model, we will face ecological collapse.

    If we do discard the endless growth model; however, we will be removing what some say may eventually be the driving force behind our colonization of space.

    Thus, if colonization of space is to take place it must arise from aesthetic and/or adventure-based motive, as it is highly unlikely given current trends that the endless growth model will propel us into space before propelling us toward ecological collapse.

    Paul, my friend, what do you think of these ideas?

    Very interesting notions, spaceman. I do think both aesthetic and adventurous motives come into play when we consider exploration, but I wouldn’t give up on the growth model just yet either. Since you ask my opinion on this, I’ll suggest that we’re at a stage of crisis in resources (or will soon be) that will demand we learn how to meet our needs through exploitation of the resources around us in the system or else go into a period of decline. If the latter occurs, the adventure motive may still be compelling, but we simply wouldn’t have the resources to make extended missions and infrastructure building possible. I don’t know which way we wind up, but I would hope we can find a way to moderate the growth model so that we solve our core resource problems without ecological catastrophe. I recognize this is a tall order, and a scary prospect to thread our way through.

  • Astronist December 9, 2011, 21:01

    Paul, I would suggest that the way through involves ramping up growth in space at the same time as ramping it down on Earth. In space population and infrastructure growth should continue, while on Earth economic growth will be increasingly confined to efficiency gains, genetics, nanotech and the like. The most important issue is energy supply; I want to look into space solar power in more detail in order to make up my mind whether this has a role to play. The other most important issue is that the colonial Solar System and metropolitan Earth remain economically linked.

    Clearly, we need a dynamic, prosperous and peaceful industrial civilisation to continue on Earth for at least the next half-millennium or so in order to fully establish ourselves on a Solar System scale (and ramp up towards an interstellar scale).

    Stephen

  • Paul Gilster December 10, 2011, 9:29

    Astronist writes:

    Clearly, we need a dynamic, prosperous and peaceful industrial civilisation to continue on Earth for at least the next half-millennium or so in order to fully establish ourselves on a Solar System scale (and ramp up towards an interstellar scale).

    Well said, Stephen, and I also like your point about expanding growth in space while growth on Earth becomes more sustainable. I think the role of space-based solar power generation will be significant as this process develops.