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Beginnings of the Interstellar Idea

My time off last week really was refreshing, although it coincided with the same heat wave that has kept the Eastern US under duress for many days now, especially dangerous for those who lost power because of severe storms. Fortunately, I used part of my time to fly to San Jose to participate in Steve Durst’s Galaxy Forum (sponsored by the International Lunar Observatory Association), where I spoke on destinations in the outer Solar System and beyond as we make our first tentative steps into the galaxy. It was a good gathering, with lively talk from Seth Shostak, Jon Lomberg, Tony Cardoza (who signs people up to travel on future flights with Virgin Galactic), and Durst himself. It was also a pleasure to meet Centauri Dreams regular Alex Tolley. Blissfully, the temperatures never got out of the low 70s, with a refreshing breeze that made walking around downtown a pleasure.

Miles, my older son, lives near San Francisco and the trip was also a wonderful chance to reconnect. I can recall walking around the Air and Space Museum in Washington with him when he was just a boy, talking about the various planetary missions and speculating about what might come next. In our San Jose conversations, we talked about the attention now being paid to interstellar flight and what has changed over the years, ideas I reflected on while flying back to the East Coast. It’s really only been in the past 50 or 60 years that scientists and engineers have focused on the problems of interstellar flight, and even then mostly as extra projects in their spare time.

How exactly did the idea grow in the scientific community, and who were the early players? In an essay on fusion propulsion in the Johnson/McDevitt book Going Interstellar, Greg Matloff fixes on Freeman Dyson as a pioneer in what we could call the ‘interstellar movement.’ Dyson had been working with Ted Taylor on Project Orion, which saw its high-water mark in the early 1960s as a propulsion system that could take astronauts on interplanetary journeys, and do so not in the cramped quarters of an Apollo-style capsule but aboard a massive vehicle that could hold a crew of a hundred or more. Orion used the explosion of nuclear devices behind a massive pusher plate to drive the vehicle, ruling out launch from Earth, but there were serious studies of using Orion principles in a Saturn rocket upper-stage, a design that could not only reach Mars in about a month but could carry greenhouses, livestock and building materials.

Image: Freeman Dyson in earlier times, when Orion ideas were in the air and all things seemed possible. Credit: New York Times.

When the Atmospheric Test Ban Treaty (1963) made Orion obsolete, Dyson wanted to save the idea, fearing it would be buried in some government vault and never resurrected. Matloff sees a cunning strategy in what happened next:

Being a physicist, Dyson planned to publish a paper describing the potential of Orion in a journal. But most physics, astronomy, and astronautics journals have circulations of only a few thousand. He chose to publish in Physics Today, a semi-popular monthly organ of the American Institute of Physics. Many public and university libraries subscribe to this magazine — its monthly readership would therefore be much larger than that of more technical physics journals. Dyson planned a paper that would outline the concept of Orion in visionary terms, and do so in a manner that would not violate his oath of secrecy.

And there’s the key, to get the Orion idea out to the public, which Dyson could do by using openly available information, such as the publicly available yield in equivalent megatons of a deuterium-fueled thermonuclear explosive. Going on to develop the Orion idea, Dyson could show that a fusion-pulse ‘worldship’ could reach the nearest stars in approximately 1800 years, carrying a colony of 20,000 to settle on whatever new worlds would be found at destination. The Dyson colony ship had an acceleration time of 500 years, to be repeated in the deceleration phase, but a much leaner Orion-based design could reach velocities of 10,000 kilometers per second, arriving at the Alpha Centauri stars in a scant 130 years.

Image: An interplanetary Orion departs for Mars. Credit: Adrian Mann.

It was the decision to make the Orion concept visible that distinguished Dyson’s approach. He had labored in Bomber Command for the RAF during World War II, an experience that made him all too aware of how a sluggish bureaucracy can stifle creativity and prevent needed change. I believe that Dyson’s starship ideas were deliberately provocative as he attempted to spark interest in the general public in a propulsion scheme he saw primarily as an interplanetary technology — he would later come to see Orion’s demand for nuclear explosives as both dangerous and impractical. But the key was to get across the fact that working within the laws of physics, a craft could be designed that could, in theory, cross the interstellar divide.

Dyson’s paper “Interstellar Transport” ran in Physics Today in October of 1968 (pp. 41-45), and it’s still a classic of interstellar studies. Tomorrow I want to dig into it in a little more detail, as we’ve never really gone through it in these pages. But I don’t want to stop with Dyson. There are a number of scientists whose early contributions helped to launch this field. Some honed their skills on the intractable problems of power and distance in scientific journals, seeing where the equations led under a variety of novel propulsion schemes, while others saw their work transformed as it entered popular culture, an outcome that few could have anticipated. All of them transformed our thinking as interstellar flight began to be seen as a remote but real possibility.

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  • Alex Tolley July 10, 2012, 12:51

    The performance envelope of Dyson’s 2 ships, and the timing of building them (200 years based on 4%/pa GDP growth and Apollo like funding) could result in these ships passing the speculative, current technology, deep space probes on their way to destinations in the Oort cloud.

    The sizes of the ships does make them seem somewhat impractical, apart from the need to explode an h-bomb every 100 seconds or so. The “conservative” design has a copper hemisphere 10 km in radius, 1 mm thick and massing 10 million tons. The ablation version with a 0.01x the conservative version total mass seems more practical, even though we are still talking about a huge vessel.

    I do love Dyson’s writing in this paper. e.g.

    Incidentally, the velocity of 10 000 km/sec is just about what one could reach by “surf riding” on the ex- panding shell of debris from a super- nova remnant like Cassiopea A. This equality may not be entirely coincidental.

    Which makes one wonder, what if we could build a “sail” (material or electromagnetic) that could surf the debris from directed explosions? How many explosions would be needed, and could they be focused sufficiently to make a viable propulsion system for a small interstellar probe?

  • Tony D July 10, 2012, 12:57

    Paul,
    Glad to see you spent some time out here in my hometown. Being smack middle in Silicon Valley and in close proximity to NASA Ames and Lick Observatory, I feel (rightfully or wrongfully so) this is ground zero for interstellar studies. Heck, if you believe science fiction, the RDA from the movie “Avatar” should be founded right here in someone’s garage within the next 20-30 years ;)

  • ljk July 10, 2012, 13:15

    Here is Dyson’s paper on Project Orion from Physics Today in 1968:

    http://galileo.phys.virginia.edu/classes/109.jvn.spring00/nuc_rocket/Dyson.pdf

  • Adam July 10, 2012, 16:36

    Dyson’s figures are meant to be taken with a grain of salt. He estimates exhaust velocities of between 3,000-30,000 km/s, and efficiency of coupling of 0.25 to get effective specific impulses of ~1,500-15,000 km.g/s. The upper range is ambitious to say the least. But that’s for devices that are almost pure deuterium which is somewhat beyond the state of the art. Fission devices would have much lower specific impulses. One thing nuclear pulse can’t do is be small – a pulse driven starship is inherently gigantic. Fission-fragment rockets might achieve similar performance in a smaller size, though they have heat-related thrust limitations. Robert Zubrin’s Nuclear Salt-Water Rocket would span a similar range of thrust and specific impulse as Interstellar Orion, but might need a few tweaks to actually achieve fission. More exotic ignition schemes will need to be explored before Dyson’s vision can be achieved.

  • David A. Czuba July 10, 2012, 18:58

    Great post. It so happens that I got caught in the Dyson orbit. I read Freeman Dyson’s book “Weapons and Hope” when it first came out (1984). I interviewed Freeman by e-mail in 2004, then moved west from Buffalo, NY, to Bellingham, Washington. Freeman’s son and author George Dyson lives just down the road. I met Freeman when he spoke at our local bookstore with the issue of his book “A Many-Colored Glass”. Lastly, when I was unemployed during 2009-2010, I took work cleaning the home of Verena Huber-Dyson, George’s mother, who introduced me to her daughter Esther Dyson, the former chief of ICANN and almost astronaut (astro-not!). It doesn’t seem possible that these folks played parts in our spacefaring future.

    George wrote a somewhat scattered telling of the story of project Orion in his book “The Atomic Spaceship”, and another author, Kenneth Brower, wrote a dual biography of father and son called “The Starship and the Canoe”, which is a very good read, but for a broad audience.

    My own father took his two sons to visit our uncle in the “other Washington” (D.C.) and I have similar fond memories of the National Air and Space Museum. Ninety minutes south of me, near Seattle, ex-Microsoft founder Paul Allen built the Museum of Flight with a warehouse waiting for the shuttle trainer. Right now, it only has a very small Soyuz re-entry capsule.

    I’m currently writing a paper discussing how knowledge divergence will occur aboard an Interstellar vessel, and what systems are needed to maintain knowledge consistency. Keep up the great dialogue!

  • Joy July 10, 2012, 20:03

    ~ Dyson’s 2 ships, and the timing of building them (~ 200 years based on 4%/pa GDP growth)

    The validity of an exponential real economic growth assumption is critical to everything we discuss here and requires some deep scrutiny. Most of us would conceed straightaway that centuries of exponential economic growth is impossible without self sustaining industrial space development, the mass production of materials and energy in space. That is problematic considering that 55 years into the space age we have not produced any materials in space and what little energy produced on our spacecraft is dwarfed by the energy required for their manufacture and launch. So how far can we go on the ground before we hit the wall? Physicist Tom Murphy at UC San Diego has explored this on his “Do The Math” blog:

    “Alright, the Earth has only one mechanism for releasing heat to space, and that’s via (infrared) radiation. We understand the phenomenon perfectly well, and can predict the surface temperature of the planet as a function of how much energy the human race produces. The upshot is that at a 2.3% growth rate (conveniently chosen to represent a 10× increase every century), we would reach boiling temperature in about 400 years… And this statement is independent of technology. Even if we don’t have a name for the energy source yet, as long as it obeys thermodynamics, we cook ourselves with perpetual energy increase.”

    Note that a 4% annual economic growth rate would reach the same 10,000 fold increase in waste heat production and boil the world’s oceans in just 235 years, ~ Dyson’s timeline. Once again, this has nothing to do with greenhouse gases as large scale fusion or any new carbon free energy source would do this.

    Some would argue rather forcefully that economic growth is independent of energy production. (The fancier dessert argument used by the economist below) Even if one buys this argument, massive fast starships are not made of fancy desserts, they are unavoidably energy intensive. Lacking a means to bootstrap exponential economic growth offworld, our future ventures will be limited to starwisps and slow ships.

    http://physics.ucsd.edu/do-the-math/2012/04/economist-meets-physicist/

  • Alex Tolley July 10, 2012, 21:54

    Lacking a means to bootstrap exponential economic growth offworld, our future ventures will be limited to starwisps and slow ships.

    A steady state economy would be a very different way of life. It’s obvious proximity almost demands a breakout into space to avoid, unless we can adapt it (forcibly perhaps). It isn’t a world I would like, but it is a likely scenario.

    Always good to be reminded of limits, and the postulated energy limit discussed in the link is very generous.

  • Rob Henry July 10, 2012, 23:06

    Joy, extrapolations by necessity use simple models. Here Tom Murphy combines the modern trends of population growth and economic growth per capita to give those boiling oceans. Given that fertility rates have plummeted below replacement values in all the most wealthy Western and East Asian countries, we should question how long this trend would be valid for anyway.

    If it is just wealth per capita that continues to rise, we may ask if it is the increasing flow of energy or information or material accumulation that becomes its limiting characteristic.

    Thus, I believe that, all Murphy has shown is that energy usage will not stand as the best proxy for wealth in a growing economy or catastrophe will result. In such circumstances most of us put our trust to market forces, but I hear your call to beware of externalities.

    I must admit though Joy, a far future where the largest cost each citizen is payment to the civil authorities for dumping their waste heat is not one that I recall being covered in Science Fiction… Very strange that.

  • coolstar July 11, 2012, 0:02

    Thanks Joy for the link to Tom Murphy’s piece on exponential growth. On reading it I found that he seems to left out the fact that his calculations are based on “waste heat” (but you didn’t!). Note that his CALCULATIONS ARE based on waste heat, which is the relevant factor (about 0.025 W/m^2 now) but his prose didn’t reflect that (unless I missed it) .

    I had to redo the calcs for myself just to be sure he was right!

    I think this is an important distinction as the burning of fossil fuels obviously isn’t a very efficient way of doing work (in the physics sense). So one might expect at least a few more doubling times if/when civilization converts to more efficient means of energy usage. Of course, “few” here doesn’t amount to a great deal on historical time scales unless we get VERY efficient.

    Earth based civilization could gain several more doubling times by decreasing the population by a large factor, as energy usage seems to scale as some power of the total pop.

  • David H July 11, 2012, 1:53

    ljk – thank you for the link.

    I emailed Professor Dyson recently regarding Orion and received an almost immediate and considered response. One of those people whom you just wish could live on in perpetuity!

    All the best.

  • Bill July 11, 2012, 3:56

    I was interested in the fact that Joy mentioned that the exponential growth required to produce the raw materials for a interstellar starship would in fact result in a what we might label for the lack of a better term “heat degraded society” with the result that further and further expansion of economic progress would doom us in the long-term. This is not the first time I heard about that but I read it previously and was so astounded by it because it seems to defy common sense as well as thermal dynamics. In giving a quick once over on thought about this would this be a possible solution to such a astounding outcome: May I suggest that if this factor is as deadly to us as it has been postulated then perhaps the idea should be put forward that solar collectors, set out and bass to raise over good deal of the useless part of the land would be used to create electrical power, split water for the hydrogen, and be utilized to further reduce trash and waste byproducts into their constituent elements. Why so? The reason is quite simple what we would be attempting to do is take the sunlight that would have to be re-radiated into space and use that directly to break down our waste products into separate elemental substances. Such a breakdown on a vast scale would in fact be used as an energy sink to absorb the excess radiation in the creation of new chemical bonds. Such substances would be able to be stored effectively indefinitely and would be NOT be able to reradiated the energy back into our atmosphere and oceans. Naturally of course if we are talking about reusing these elements then there chemical energy would be re-released and have to be dealt with. It’s these set abilities to store energy in many different forms that would permit us to stave off such thermal problems.

  • Richard July 11, 2012, 7:01

    Low 70’s!! I wish we’d get low 70’s over here across the pond. Except for a day or 2, 3, it’s been mid 50’s to low 60’s since like April over here.

  • Adam Crowl July 11, 2012, 7:04

    Hi Joy

    Funny you should say that… Affordable, Rapid Bootstrapping of Space Industry and Solar System Civilization …might be the pill to cure that ill.

  • Alex Tolley July 11, 2012, 10:24

    @Adam
    I just love the last line in the slide deck:
    “Full details are available in the ISRU Special Editon of the Aerospace  Engineering (JAE), ASCE Aerospace Division”.

  • Alex Tolley July 11, 2012, 10:39

    @Bill

    The article effectively covers your point. The author points out that even allowing for high energy efficiency the heat limitation calls a halt to growth, and secondly the heat emitted would result in the surface of the earth needing to be hotter than the sun. No amount of solar energy conversion, even at near 100% efficiency is going to offset the problem.

    The logic is quite clear. Unless we have a way to increase GDP without increasing energy usage (unlikely), eventually a planet reaches a limit of civilization level it can support. We cannot even use the abundant resources of the solar system if they incur extra waste heat losses on earth – so solar power sats are limited, asteroid metal processing and working on earth must be limited, even dropping finished goods using atmospheric breaking is limited.

    One way out might be to build a space elevator-like structure and use it to move waste heat to be radiated away in space, thus circumventing the problem. In effect, building a refrigerator cooling the earth.

  • Kelvin July 11, 2012, 11:52

    Thanks for the good article Paul. My personal opinion is that “interstellar studies” began as a credible science in 1952, with the publication of Dr Les Shepards paper “interstellar flight” in JBIS. This was the first ever technical publication addressing the problem and potential solutions and was therefore the start of the long roadmap ahead.

    Tony D, the British Interplanetary Society has been the home and “torch bearer” for interstellar studies for many decades. So I would argue this is ground zero (London) for interstellar, although San Fancisco (Starfleet Academy) gets a close second place for the contributions in communicating the vision.
    ;-)
    Kelvin

  • ljk July 11, 2012, 13:51

    Kelvin said on July 11, 2012 at 11:52:

    “Tony D, the British Interplanetary Society has been the home and “torch bearer” for interstellar studies for many decades. So I would argue this is ground zero (London) for interstellar, although San Fancisco (Starfleet Academy) gets a close second place for the contributions in communicating the vision. ;-)”

    And since most of the pioneers of the Search for Extraterrestrial Intelligence got their careers in that field going at Cornell University – Philip Morrison, Guiseppe Cocconi, Frank Drake, Carl Sagan (Charles Townes, the inventor of the laser and early promoter of Optical SETI, was accepted at that institution but chose California instead – just for the record) – Ithaca, New York, may be considered the home of SETI.

    There also seem to be a disproportionate amount of UFO sightings in the region, too, so there must be something in those Finger Lakes. :^)

    We are going to need a good SETI program if we want to know where and where not to send our interstellar probes and Worldships.

    As for meeting Freeman Dyson, I have now been at three different events since 2000 where I was in his presence, but I was unable to even say hello to him due to the mobs of people surrounding the man. All I ever wanted to do was tell Dyson how much I like his vacuum cleaners.

  • Rob Henry July 11, 2012, 17:29

    Alex Tolley, by bizarre coincidence I thought of the same weird refrigerant conveying space elevator solution as you, but I came to another conclusion. My imagination could not stretch to it being sufficiently efficient as to work for Earth, but it could for the case of Mars. If so this could give a larger effective radiating surface area than Earth, and one that can be adjusted according to human requirement, rather than that of an entire biosphere.

    Thus my extrapolation of this thought had us all living on Mars, and Earth becoming a quaint wildlife park.

  • Astronist July 11, 2012, 19:30

    From Tom Murphy’s blog:
    “Physicist: I assume you’re happy to confine our conversation to Earth, foregoing the spectre [sic] of an exodus to space, colonizing planets, living the Star Trek life [sic], etc.
    Economist: More than happy to keep our discussion grounded to Earth.
    Physicist: [sigh of relief: not a space cadet]”

    Exactly. He reaches his anti-growth conclusions precisely by deliberately excluding the one essential precondition for growth to continue.

    Joy, you suggest that because we’ve not yet begun to colonise space after 55 years, it will therefore never happen at all. I wonder whether you would agree that similar arguments could have been made regarding the colonisation of North America (first permanent European settlement was Jamestown in 1607, more than 600 years after the Vikings first reached North America) or regarding human atmospheric flight (first aeroplane flight more than 400 years after Leonardo da Vinci sketched his flying machine, and 1500 years after a Chinese book described a flying car kept aloft by spinning blades, according to the vacuum salesman’s History of Great Inventions)?

    Clearly, the question is not how much time has passed since an idea was first mooted, but whether progress in the right direction is occurring. The rise of a number of commercially oriented space companies tells us that, for the present, progress is very much happening.

    Stephen
    Oxford, UK

  • A. A. Jackson July 11, 2012, 19:51

    Alex Tolley’s mention of Dyson thinking about ‘surf riding’ a supernova had been in my mind when I did a special topics research paper for supernova expert David Arnett when I was a graduate student at U of Texas.
    I remember him being amused by it when we were talking about supernova.
    In the years since I have totally forgotten that was the seed of the idea for that science fiction short story …SUN’S UP by Howard Waldrop and me!
    Howard and I probably ought to dedicate that story to him.

    Dyson was not quite the magician Feynman was , but more than a genius.
    I don’t know how one gives credit to a scientist who made it possible for Feynman , Schwinger and Tomonaga to receive the Noble prize, when he showed the theories were the same:
    F. J. Dyson (1949). “The radiation theories of Tomonaga, Schwinger, and Feynman”. Phys. Rev. 75 (3): 486–502

    I did my graduate work in gravitational radiation, in the 70’s, and can remember my adviser telling me to read Dyson’s:
    Seismic Response of the Earth to a Gravitational Wave in the 1-Hz …
    Astrophysical Journal, vol. 156, p.529
    He did the calculations using group- theoretical considerations, man!, I was blown away!

  • Astronist July 12, 2012, 7:24

    In fact, Paul, can I please register a plea that CD addresses more often the problems of developing our monoglobal civilisation into a multiglobal one? To my mind this is critical for the starship enterprise. Joy has from time to time indicated how important it is. I am sure that a sizeable proportion of people outside this forum take the view that industrial civilisation is unsustainable (as Tom Murphy likes to warn it may be), and certainly won’t grow to the point, technologically or economically, that it’ll ever be able to afford the immense interstellar enterprise.

    Stephen

  • Keith Cooper July 12, 2012, 10:14

    @ Alex Tolley,

    Dyson’s comment about surf-riding supernovae shock waves is intriguing for SETI. Perhaps an anomalous number of supernovae in close proximity over several hundred to several thousand years might be a colonisation wave moving through a galaxy? Perhaps mapping supernovae remnants may be a way to uncover such a wave.

  • Alex Tolley July 12, 2012, 11:14

    Let’s run with some numbers for energy and GDP based on the Dyson paper and the link Joy provided.

    Dyson assumes 4% growth, which after 200 years yields a GDP (and presumably energy demand) of ~ 2500x 1968 US GDP.

    The Finite Physicist claims that in 400 years of 2.3% GDP growth, lots of energy efficiency, we use the total energy striking the earth. That results in a GDP around 9000x global GDP. That would mean that even Western levels of consumption might rise 100x that of today.

    Suppose we need to increase that further without too much space cadetry.
    let’s hypothesize a space elevator than extends a tether beyond geosync and terminates in solar energy converters. Let’s assume that extended radius is 200,000 km. Assume build out so that lots of elevators create a cylinder of solar panels with a a total height of earth’s radius and a radius of 200k km. That gives us an area of 15x that of the earth, allowing a further 10x GDP without too much problem of heating the planet. So now Western GDP is 1000x 2000 levels, and global GDP 90,000x. (It might take heroic energy transfer along the elevators to keep the planet cool!).

    Perhaps enough to build starships?

    Logically, if we can build such a structure, why stay on earth? I chose 200,000 km radius, because the inner surface, rotating every 24 hours, would provide 1g of artificial gravity. Industry, agriculture and eventually part of earth’s population could expand onto this surface, 15x larger than the earth. A mini Dyson sphere/Ringworld tethered to the earth. More room to expand than populating the inner planets of the solar system, and all within easy communication and transport distance with earth. 200km walls would allow an atmosphere to be held to the surface with relatively small losses, offering an open sky with the earth dominating the view. (Is this an original SFnal idea?). Starships, should we wish to build them, could be build in space docks at geosync, with easy transport from either earth of the ring. Perhaps a rail gun around the circumference of the ring could be the initial launch pad.

    While there is a lot of handwavium involved, does this get humans to a high material state of welfare and keep the future open enough to allow us to escape the Malthusian/energy trap to expand to the stars?

  • Rob Henry July 12, 2012, 16:17

    Alex Tolley, you seem to realise the problem with that space elevator supporting a ring since you ask for lots of Handwavium. When I first heard of the concept for Earth, I calculated that there was to much tension to support even the weight of the cable itself in Earth’s case, even for the greatest theoretical chemical bond strength. I thought that they had made a mistake, until I found that the plan was to taperer it.

  • Paul Gilster July 12, 2012, 16:55

    Astronist writes:

    In fact, Paul, can I please register a plea that CD addresses more often the problems of developing our monoglobal civilisation into a multiglobal one?

    Point taken, Stephen, though our focus here is primarily on science and engineering and the places where they converge. I agree with you on the importance of the issue and am delighted when the debate over it is high-quality, such as the byplay here between you, Joy and others. What we really need is for someone to develop and devote time to a site explicitly looking at these issues in relation to future space development. That would be a true contribution to interstellar studies, and one I don’t have time to do.

  • Holger July 13, 2012, 11:52

    @Rob Henry:
    My impression was that recently developed materials (carbon nanotubes) come close to the strength needed for a space elevator, and that an elevator-strength material would not contradict known physics/chemistry.

    I agree that Alex Tolley’s “ringworld” with a 200.000 km radius would likely not at all be feasible (it would require so many elevators that their mass exceeds that of the ringworld), but one with a radius of 42.000 km plus a little (giving ~ 3 times Earth’s surface area) might be:
    The counterweight for the elevator cable outside geosynchronic orbit can be made arbitrarily large by putting it very close to the geosync. orbit, without any additional tension on the sub-synchronic part of the cable AFAICS.
    Of course, such a ringworld would have close to zero gravity (being almost in orbit itself), so would not be very comfortable for human inhabitants…

  • ljk July 13, 2012, 14:38

    Keith Cooper saidon July 12, 2012 at 10:1:

    “Dyson’s comment about surf-riding supernovae shock waves is intriguing for SETI. Perhaps an anomalous number of supernovae in close proximity over several hundred to several thousand years might be a colonisation wave moving through a galaxy? Perhaps mapping supernovae remnants may be a way to uncover such a wave.”

    In addition to that intriguing idea, supernovae should also be checked for METI from ETI between the SN and Earth. The idea is that since supernovae are some of the brightest known natural objects in the Universe, they would attract the attention of astronomers among others. A smart society desiring to make contact would aim their transmission in the direction of space opposite to the stellar explosion.

    http://cosmoquest.org/forum/showthread.php/120803-Supernova-boosted-Radio-Transmissions?s=5fa62f2acab9249cdde564aa7f8668d7

    And James Gunn’s 1972 science fiction novel The Listeners involves ETI about to be destroyed by the violent deaths of their suns (and apparently unable to escape their solar systems en masse or even en little) transmitting the vast knowledge of their societies to other worlds in the galaxy as a form of preservation with the bonus of expanding our knowledge.

  • Rob Henry July 13, 2012, 18:08

    Holger, we may disagree as to whether an UNTAPERED space elevator is possible for a normal matter cable in Earths case, but we agree that one at 200,000 km is not. Yes, the problem was not whether that ring was possible, but that for every kg we placed at its surface, we would have to have a ridiculous number of them further down.

    Your ring starting 36,000 km above the Earth is feasible by comparison. Its radius would have to be adjusted outwards and its surface gravity increased as evermore tethers are dropped down from it, but I am intrigued to know whether such a system could be made to hold an atmosphere the traditional ringworld way (that is without a physical roof) under any reasonable circumstances.

  • Alex Tolley July 14, 2012, 0:32

    @Rob Henry, Holger
    Could the ring at 40km be spun up so that it is traveling > synchronous orbital velocity? That would allow g forces to be experienced, while tethers could be more like bridge suspension elements. The problem would be how to attach the tether to the ring – perhaps with some sort of magnetic rail?
    G forces would then allow a ringworld like contained atmosphere behind sufficiently high walls.

  • David A. Czuba July 14, 2012, 1:05

    With regard to economic growth, we must keep in mind that it is information fueling such growth, and not simply access to resources. Aboard the starship, zero-sum economic activity like time banks will serve for exchange until the destination is reached. Then, the database recipes are tapped to begin colonizing, replicating processes modeled from earth to mine resources. There need not be growth until the destination. Now, the interesting thing about behavioral dynamics in large organizations is that people work effectively confronted with an important opportunity. Game-maker Jane McGonigal points out that motivation is informational, and so may be guided by designed-database input. This is one reason gaming is so addictive. By the arrival at a destination, the starship’s crew has generational education that has embedded certain specific procedural responses to various mission opportunities. I suppose starship crews should be thankful for being relatively small by comparison with planet-bound populations, since their resourcefulness will be rewarded with explosive growth…in a couple hundred years.

  • Rob Henry July 14, 2012, 17:48

    Alex Tolley, until now all options discussed here involved cables that were directly attached to both the Earth, and ringworld. If cables were dropped from that geosynchronous position, but not tethered to Earth or touching its atmosphere, then they would also allow/facilitate a spin up. This sounds easier than using a rail. Unfortunately, my suggestion would not have the same degree of inherent stability as yours, but could be built with ordinary matter.

    Your insistence on one g remains the big problem. Anyhow, Mars still looks better for most extreme options using cables of ordinary matter.

  • strappolee@gmail.com July 16, 2012, 14:39

    I recently got a “B” in my English 103 honors class,
    my topic,
    “A Carbon Taxed fueled social security sovereign wealth fund”

    my premise is that a carbon tax reduces CO2 consumption and that the carbon tax would be invested in the worlds capital markets and in “industrial policy”
    I used several online calculators to Gage growth of a $250 Billion tax invested in the newborn children born that year and every year afterwords.
    this allows the funds to grow for 65 years before a benefit is do.I used a 4.5% growth rate to account for inflation and discovered that $250 Billion times 65 years yields just short of $100 Trillion.in 65 years the world GDP will only be three times this amount so I think you would have to invest in off world projects since it would not be sustainable for this fund to own that much of the capital markets.I believe you would add the worlds GDP to the funds value to arrive at a new total world GDP, this courses 50 years from now inflation so…………………
    I would transfer the Tennessee valley authority and the Columbia river authority to this fund and build a fleet of heavy water nuclear reactors to utilize the PWR fleets spent fuel ( it would take over 50 reactors)these federal utility’s are at their maximum borrowing limits so the sovereign wealth fund would capitalize the building of this fleet.
    This project spread over thirty years would result in close to a Trillion in assets.
    the next step would be to build a fleet of space based solar and nuclear power generators at a cost of 5% of the sovereign wealth funds total assets or $5 trillion, the prudent person rule would not allow a pension fund to risk money in any one investment so we have to be cautious in using this fund on “industrial policy”
    building energy infrastructure on such a scale adds to the workforce that is paying into the existing social security system and full employment would moderate our cyclic business cycle
    in a century this social security sovereign wealth fund would(sorry not in 65 years)would replace the old social security system and no one over 65 years of age would be eligible for poverty assistance.Using a carbon tax to end poverty with investment dividends would take a century but my second premise is that a society distracted by poverty and war is unlikely to lead to a world civilization that would embark on a interstellar exploration campaign.
    the tens of thousands of employees of the space based power sats and infrastructure to maintain and build them out in cislunar space would be the nuclei to a solar system GDP that would begin to accelerate its growth outwards………………….

    http://www.komanoff.net/fossil/CTC_Carbon_Tax_Model.xls

    http://www.vertex42.com/Calculators/savings-interest-calculator.html

    http://www.apfc.org/_amiReportsArchive/APFC%20Annual%20Report%202011.pdf

  • Eniac July 16, 2012, 22:52

    Once again I feel the need to point out that the relation between growth in GDP and growth in energy use is completely outdated in this century. For quite a long time now, most growth is happening in industries that have very little relation to energy use: health care, finance, entertainment, law, politics, etc. etc. Furthermore, even the more material industries have gone towards miniaturization and use of less energy, witness the iPad vs. the PC. More value, less energy.

    If you look at the purportedly exponential growth in Murphy’s chart, you can see that quite clearly. The data is not at all like the straight line that is plotted through it. If you disregard the confusing straight line, you can see that energy growth is tapering off very significantly. I consider it likely that it will reverse at some point, with the economy nevertheless merrily growing at 3% all the while. Possibly much faster, now that it is freed from the shackles of physical resources and energy.

    With regards to starships, the energy used by a starship is produced in space, by the engine, using the fuel. Thus, the question is not how to get that much energy, but only how to get that much deuterium, or whatever the fuel of choice will be. And, of course, how to build the engine. How much energy we use on Earth to heat and cool our homes and fill our tanks has precious little to do with either of these.

  • Eniac July 16, 2012, 23:07

    The Ring World around the Earth is actually quite feasible. As Holger pointed out, all that needs to be done to overcome material limitations is to move it closer in, reducing its surface gravity and with it the stress on spokes and/or rim. My spontaneous guess is a reduction to 1/2 or 1/3 g will be sufficient to obviate the need for unobtainium.

    Speaking of spokes and rim, once the circumference is complete, no spokes are actually needed. The rim alone will hold things together. The structure is not inherently stable, but that can be addressed by many different methods, with or without spokes.

  • Hop David July 17, 2012, 10:31

    It seems to me interplanetary travel would become routine long before we’d try interstellar travel.

    If our civilization isn’t restricted to earth’s surface, we could continue exponential energy growth for a longer time. Adding the surface areas of rocky moons and planets as well as the asteroids would give us far more surface area to radiate heat from.

    In his posts “Why Not Space?” and “Stranded Resources” Murphy argues that even settlement of the solar system isn’t likely. However Murphy’s arguments are suspect.

    For example Murphy’s “Grab That Asteroid!” scenario specifies a kilometer sized asteroid requiring 5 km/s for retrieval to earth’s neighborhood. Murphy suggests using lox/methane as reaction mass which if I remember right, has an exhaust velocity of around 3.3 km/s.

    Contrast “Grab That Asteroid!” with the Keck proposal: .17 km/s to retrieve an asteroid and park it in high lunar orbit and an ion engine. Exhaust velocity of their ion engine would be about 30 km/s

    Plug these quantities into the rocket equation:
    (propellant mass)/(dry mass) = e^(dV/Ve) – 1

    (propellant mass)/(dry mass) = e^(5 /3.3) – 1 = .94
    vs
    (propellant mass)/(dry mass) = e^(.17 /30) – 1 = .0057

    In Murphy’s scenario it takes nearly the asteroid’s mass in propellant to retrieve it. In the Keck proposal, the asteroid outmasses propellant 176 fold.

    There are many other flaws with Murphy’s arguments that I could talk about but this post is already long enough.

  • Holger July 18, 2012, 13:27

    @Rob Henry:
    Right, I forgot to account for the atmosphere in my suggestion. I don’t know how high a gravity is needed to keep an Earth-like atmosphere at least for some decades/centuries (during which time it could be replenished). Centrifugal force at constant angular speed is proportional to the radius, and increasing the ringworld’s radius e.g. to 84,000 km (which would be feasible with any space elevator material, and still require less elevator mass than ringworld mass) would result in a centrifugal force of 0.42 m/s^2; subtracting gravity gives 0.37m/s^2 net acceleration, so some 0.04 g.

    (After doing the calculation myself, I think Alex Tolley actually miscalculated the distance needed for 1 g: at 200,000 km distance, you would only have a centrifugal acceleration of 1 m/s^2, or a tenth of a g, when moving at one orbit per 24 hours; you’d need 2 million km distance for 1 g, further than the Moon! So there is no way for a ringworld with less mass than the elevators to have more than 0.1 g, as Eniac had hoped. Unless I miscalculated myself.)

    @Eniac:
    Murphy’s energy data do fit an exponential curve quite well for the 360-year timespan IMO. But you’re right that the growth is substantially lower in the past ~40 years. The question is if this is a “short-term fluke” like former slight deviations from exponential growth in the diagram, or if the “limits to (energy) growth” are finally showing…

  • Eniac July 19, 2012, 22:22

    @Holger:

    Murphy’s energy data do fit an exponential curve quite well for the 360-year timespan IMO.

    I am not convinced. Just from looking at the plot, you can tell that a quadratic fit would be very much better. So much better, in fact, as to render the linear hypothesis laughable in comparison.

    You are likely correct about the lack of “gravity” on a geostationary ring. You’d have to rotate the ring, but then there could be no more spokes and the maximum acceleration given material limits may still be much less than 1g.

  • Holger July 20, 2012, 12:23

    @Eniac:
    “I am not convinced. Just from looking at the plot, you can tell that a quadratic fit would be very much better. So much better, in fact, as to render the linear hypothesis laughable in comparison.”

    I am not convinced by this either. A quadratic fit would indeed be somewhat better than a linear one, but that is natural given that it has one more free parameter to choose. (The maximum of such a quadratic curve would still be centuries in the future, I think.)
    And since exponential processes are much more common than “quadratic-exponential” ones (I don’t know any such natural processes), I think it is a valid assumption to use a linear fit here, which fits surprisingly well IMO, when considering the whole timespan covered.

    I would be interested to see a version of Murphy’s graph measuring energy per capita, however, and preferrably for the whole world, not just the US. While US energy consumption multiplied by a factor of ~50,000 over the past 360 years, US population also increased by a factor of 6,000 (according to http://en.wikipedia.org/wiki/Demographic_history_of_the_United_States), so the energy consumption per capita has increased less than 1% annually during that time!
    The slight decrease in the slope over time might just be due to the slightly subexponential growth of the US population (from an initial factor-of-five increase every 50 years to a mere doubling every 50 years).

  • Eniac July 22, 2012, 17:56

    @Holger

    The slight decrease in the slope over time…

    As an exercise, you may want to take a ruler to the plot and fit the slopes for the first 100 years and also the last 100 years. You will discover that the change is anything but “slight”. Exponential plots can be very deceiving like that.

    And since exponential processes are much more common than “quadratic-exponential” ones (I don’t know any such natural processes), I think it is a valid assumption to use a linear fit here, which fits surprisingly well IMO, when considering the whole timespan covered.

    You could argue conversely: No exponential growth can go on forever, thus we would not expect a straight line, it would be unnatural. A saturation curve would be more natural, and I bet will fit even better than the quadratic.

    While US energy consumption multiplied by a factor of ~50,000 over the past 360 years, US population also increased by a factor of 6,000 (according to http://en.wikipedia.org/wiki/Demographic_history_of_the_United_States), so the energy consumption per capita has increased less than 1% annually during that time!

    Now this I like. It shows how looking at things in a different way makes them appear much different. Murphy tends to pick a particular point of view which makes his position appear obviously correct and then harp on it.

  • Eniac July 22, 2012, 19:51

    Interestingly, Murphy himself has commented on the badness of the exponential fit, and proposed a logistic curve instead. In exhaustive detail, as is wont to:

    http://physics.ucsd.edu/do-the-math/2011/08/does-the-logistic-shoe-fit/

  • Eniac July 22, 2012, 21:11

    What we are really looking at here is the Energy/Gross Domestic Product (E/GDP) ratio, as mentioned here:

    Taking a long-term perspective, and using the simple Energy/Gross Domestic Product (E/GDP) ratio, the amount of energy needed to produce a dollar’s worth of goods and services in the U.S. economy fell by more than half between 1949 and 2004.

    From http://www1.eere.energy.gov/ba/pba/intensityindicators/total_energy.html

    It is steadily decreasing. If it keeps decreasing that way it will not be long until energy is a very minor component of GDP. How much energy is really required to file a lawsuit, compared to what an average lawyer will charge for this service? A computer consultant can make $100 an hour just sitting by himself on a sofa with a laptop. What is the energy efficiency of that particular economic activity? How about an Internet company run by three guys in a garage creating billions in value? What is the E/GDP on that?

    So, I believe that it is quite clear and obvious that it is very much possible to grow GDP without growing energy use (or any other kind of material resource), which renders all of the above mentioned arguments about the limits of growth irrelevant.

    In the US, we appear to have reached this point, as this plot of energy use vs. GDP indicates: http://notable.wordpress.com/2007/04/07/us-energy-usage-trends/

  • Holger July 23, 2012, 15:29

    “You could argue conversely: No exponential growth can go on forever, thus we would not expect a straight line, it would be unnatural.”
    That doesn’t make sense, 360 years is not “forever”.
    But I agree that the logistic growth assumption (unlike the “quadratic-exponential growth” assumption) is both more realistic and a better fit than exponential growth, so is indeed a better model. So Murphy missed his best argument/evidence against eternal energy growth in his original post…

    But the question remains if this growth pattern is due only to the similarly logistic growth of the US population, or to real energetic reasons.

    The E/GDP chart is not quite “steadily decreasing”, but it does show this tendency. I certainly agree that GDP growth can in principle be completely independent of energy growth; there’s your example of possible infinite exponential growth…
    (Murphy’s “energy villain” argument against this would only work if someone could buy all the world’s energy supply all at once for a cheap constant price; in reality, energy prices would go drastically up before the “villain” has bought most of it, impeding him from buying it all; or a government would break such an energy monopoly – so he wouldn’t even try to start such a futile attempt, and prices can stay arbitrarily low.)

  • Rob Henry July 24, 2012, 22:34

    Earlier, when I planned a ringworld around Earth, I said that a ring could be produced best if we drop the requirement for stability, lower the gravity, and just have those tethers *orbiting* at a faster than geosynchronous rate. Now I realise that the wasted counterbalance weight implicit in such a suggestion could form another ringworld – this one where the Earths gravity dominates.
    My improvement would be as follows.

    Take an angular rotation w, around the Earth such that w^2 = 4*10^-8 per square second. Now take Martian gravity as ideal at around 4 m/s/s. At 100,000 km g = Martian, and so does Earth’s gravity at 10,000 km less centrifugal force.

    Despite the distances to their neutral *balancing* points being very similar, but the terminal end acceleration being only 40% of a tether to geosynchronous orbit, I realise that the force sustained tails off very much slower with height here, so that the total tension held here may be greater. However, I am convinced that something not too dissimilar from this could be made to work with normal matter, if it can be stabilised.

  • Eniac July 25, 2012, 23:36

    Holger:

    The E/GDP chart is not quite “steadily decreasing”, but it does show this tendency.

    Well, it has been decreasing from 1.4 to 0.7 since 1969, with not a single year in which it went up, as far as I can tell from the graph. I would venture to call that “steadily decreasing”, even over your objection.

    Note also that it is only petroleum that can reasonably be said to be running out. Petroleum accounts for about a third of our energy budget, mainly transportation. Coal and gas are good for centuries, and nuclear and renewable are good forever. That and the decreasing reliance on energy to drive GDP growth have convinced me that the Oil Drum Drivel you hear all around is just that. In a hundred years, the mention of fossil fuel will elicit feelings similar to those we have now when we contemplate that whale oil was once a major source of energy. A peculiar combination of disbelief, amusement, and shame.

  • Rob Henry July 26, 2012, 18:35

    Eniac, given that what I have seen on Oil Drum has always been keen to emphasise that we are not running out of oil, but running short of the cheap and rapidly extractable stuff, I’m not entirely sure that their view is more correct than the *businesses as usual* view. Sure, fracking has slightly elevated the expected shock of price increase for oil (and greatly so for gas in many places), but the true measure is how much of the economic sluggishness of the last few years is due to this transition.

    May I be so bold as to suggest the slow takeoff of any economic recovery recently could be fundamentally due to these pressures, and the PR disaster of nuclear power in Japan might lengthen the period of transition. Given the sites such as Oil Drum are forced into the business of overemphasising the worst possible case that they can conceive of, I think that it is premature to call them wrong. A better measure of whether they are correct is to predict this slowdown will last another couple of decades, during which space exploration will more frequently be viewed as a flight of fancy.