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‘Island-Hopping’ to the Stars

We tend to think of interstellar journeys as leaps into the void, leaving the security of one solar system to travel non-stop to another. But a number of alternatives exist, a fact that becomes clear when we ponder that our own cloud of comets — the Oort Cloud — is thought to extend a light year out and perhaps a good deal further. There may be ways, in other words, to take advantage of resources like comets and other icy objects for a good part of an interstellar trip. That scenario is not as dramatic as a starship journey, but it opens up possibilities.

Let’s say, for example, that we only manage to get up to about 1 percent of lightspeed (3000 kilometers per second) before we run into technical challenges that are at least temporarily insurmountable. Speeds like that take well over 400 years to get a payload to Centauri A and B, but they make movement between planets and out into the Kuiper Belt and Oort Cloud a straightforward proposition. A civilization content to create way-stations and take its time could establish habitats all along the way, its distant descendants reaching the next solar system.

The idea takes me back to the island-hopping of Polynesian cultures as they pushed ever deeper into the Pacific, which is sometimes invoked to describe a civilization expanding from star to star. But the ‘island-hopping’ may actually involve small, dark objects exploited step by step all the way across to the target star, a process that could take millennia. A space-faring culture at home in the dark outer regions emerges. All of this depends, of course, upon the resources available, but the Oort Cloud is thought to be vast, comprising perhaps trillions of icy and rocky objects, a supply of raw materials on which such a culture could thrive.

Nomads Between the Stars

Adam Crowl recently passed along a new paper that takes this idea to another level. Louis Strigari (Stanford University) and colleagues have been looking at unbound objects, free-floating planets formed either directly in the collapse of a molecular cloud or ejected due to gravitational interactions in a solar system. Right now we know little about such rogue planets — Strigari and team call them ‘nomads’ — but they are quite interesting from the interstellar expansion standpoint as they, too, could provide even more stepping stones to distant destinations. Moreover, they cannot be ruled out as worthwhile targets on their own, as the paper suggests:

The name “nomad” is invoked to include that allusion that there may be an accompanying “flock,” either in the form of a system of moons (Debes & Sigurdsson 2007) or in its own ecosystem. Though an interstellar object might seem an especially inhospitable habitat, if one allows for internal radioactive or tectonic heating and the development of a thick atmosphere effective at trapping infrared heat (Stevenson 1999; Abbot & Switzer 2011), and recognizes that most life on Earth is bacterial and highly adaptive, then the idea that interstellar (and, given the prevalence of debris from major galaxy mergers, intergalactic) space is a vast ecosystem, exchanging mass through chips from rare direct collisions, is intriguing with obvious implications for the instigation of life on earth.

It’s a dizzying thought when you couple this with the paper’s estimates on the number of free-floating planetary objects. The authors estimate there may be up to 105 compact objects per main sequence star in the galaxy that are greater than the mass of Pluto. The mass function of the lowest-mass nomads is modeled from what we see in the Kuiper Belt and the distribution of diameters in KBOs, while at the higher end (corresponding to masses several times that of Jupiter), evidence exists that nomads in open clusters follow a smooth continuation of the brown dwarf mass function. Drawing in evidence from microlensing as well as direct imaging, the paper goes on to suggest a galaxy in which the space between the stars is well populated with objects of planetary mass, most relatively small but some larger than Jupiter.

The authors acknowledge that much uncertainty exists about the mass function as we move from larger to smaller nomads, which makes space-based observations critical for refining these estimates. One way to move forward is through a survey of the inner galaxy (the proposed Wide-Field Infrared Survey Telescope, or WFIRST, could be significant here), while large scale galaxy surveys like the Gaia mission and the Large Synoptic Survey Telescope (LSST) should be sensitive to nomads greater than Jupiter mass. Even Kepler may come into play, as any anomalous microlensing events it encounters could imply a high value for the number of nomads between the stars. From the paper:

…we note that an additional outcome of the observational approach discussed above, especially regarding the detection of short timescale microlensing events, is that upper limits may be set on the density of nomads. This could set very interesting constraints on the population of planetesimals in nascent planetary systems.

Indeed. If resources like these are available in quantity between the stars, then a pattern of slow expansion would make interstellar migration almost inevitable if humans (or their machine surrogates) can adapt to life in the outer Solar System and beyond. Propulsion is always a huge issue, but in this scenario we also focus on the ability to build and maintain habitats on distant objects, exploiting their raw materials and preparing for the next leap outwards. Long-haul technologies would surely arise from a culture capable of these things, but the possibility exists that interstellar travel will mean slow and steady outpost building before the target is reached.

The paper is Strigari et al., “Nomads of the Galaxy” (preprint).


Comments on this entry are closed.

  • Eniac February 16, 2012, 23:31

    @Rob: I find it a little hard to believe that fission fuels should be available only in the Earth’s crust. If anything, I would expect the crust to be depleted in heavy elements, since they should tend to accumulate in the core. The other rocky bodies in the solar system should contain at least similar amounts, so should the rocky fraction of the icy bodies further out, including in the Oort cloud. So I would question the premise that Earth will remain the sole source of nuclear fuel for long. Plus, likely there will be fusion, which should make fission fuel obsolete pretty darn quick.

    I also disagree with your assertion that solar power satellites will make energy cheap on Earth. Energy is already very cheap, and it is very difficult to imagine that beaming it from space to the ground, even if it were feasible and efficient somehow, could ever be economical compared to terrestrial photovoltaics and nuclear power.

  • Max February 17, 2012, 4:51

    What’s the point of sending embryos to another star system? Why would people do that?

  • Terraformer February 17, 2012, 8:15

    An important detail to bear in mind is that the energy that is put into melting ice isn’t necessarily lost, since it can be recovered by using it to drive a heat engine. Whether this would allow viable mining of uranium, I do not know. If there is a subsurface ocean beneath a thick ice crust, however, that changes the game significantly, since energy can be tapped using the temperature differential between the ocean and the surface. Also, if there are moons surrounding such a body, their gravitational potential could provide a lot of power. Coupled with starlight and fission supplies…

    Close in, in the inner Oort cloud and Kuiper belt, solar energy is going to be easier to capture. Sure, you may only be able to capture a kilowatt per square kilometer when you’re 1000AU out, but if you can manufacture solar sail quality mirrors in sufficient quantities… also, what sort of energy use are we looking at? 10kW per person? 100kW?

    I do like the idea though of Oort cloud empires linked by torchships, maybe several hundred AU across.

  • jkittle February 17, 2012, 13:36

    thorium might become the currency ( “gold standard”) of the solar system, if the development of fusion is delayed. Mining the moon makes a lot of sense environmentally and in terms of launching materials to the outer systems. Mars is also very favorable. The need for a currency to exchange is actually pretty important for an industrial society- information exchange is limited in value if you do not have the raw materials to build a minimal colony, provide for power ( electricity and heat) and feed its people.
    still hard to see us getting to far on such a limited and dirty resource.

  • Rob Henry February 17, 2012, 14:52

    Eniac said “I find it a little hard to believe that fission fuels should be available only in the Earth’s crust. If anything, I would expect the crust to be depleted in heavy elements”

    So it seems that I was not the only one who was surprised when I first found out that typical levels of uranium and thorium are at least 1000 times higher in the Earth’s crust than meteorites.

    Also remember the propaganda around about the 80’s that power satellites would save the world from energy crisis and lower the cost of energy, and the first one would still eventually pay for itself even if all material was launched from Earth? Oh, ye of little faith.

    And yes there SHOULD be fussion, but this is plan B.

  • Rob Henry February 17, 2012, 15:22

    Terraformer, the potential gravitational energy of those moons really does look enticing now that you mention it. Can you think of a way to tap it rapidly that does not take too massive an infrastructure?

  • Ole Burde February 17, 2012, 16:22

    “….and it is very difficult to imagine that beaming it from space to the ground, even if it were feasible and efficient somehow, could ever be economical compared to terrestrial photovoltaics and nuclear power ”
    Theoreticly microwawes can be transmitted to earth and converted to electric power LOCALY with a 70% eficiency , at least acording to Gerald O’Neils calculations . If anyone has ever prooved him wrong , I have not been capable of finding it anywhere ?
    The ISS has a big enough generating capacity to be capable of making a relevant experiment with the transmitting of microwawes . This was , for some people , one of the stations major reasons to exist , but was aparently scrapped for political reasons .

  • Rob Henry February 17, 2012, 17:25

    Ole Burde, you’re underplaying the advantages of power satellites. You should have also noted that they collect 4 times as much sunlight per area as an equatorial photovoltaic station would give if Earth was stripped of its atmosphere and, when we replace that atmosphere, we find that there is much more maintenance needed for that terrestrial equivalent.

  • Rob Henry February 17, 2012, 17:34

    @terraformer to generate food for the population at 1% efficiency we would need 10kW per person. In an environment were energy costs are superlatively high wrt all else, we would not need much more than this – even if everyone lives in their own well insulated palace.

  • Eniac February 17, 2012, 20:19

    Theoreticly microwawes can be transmitted to earth and converted to electric power LOCALY with a 70% eficiency , at least acording to Gerald O’Neils calculations . If anyone has ever prooved him wrong , I have not been capable of finding it anywhere ?

    This is one case where theory is miles away from practice. I am sure the theory has merit, but there are so many hurdles not considered by the theory, that the only thing of value here would be proving it right by experiment. All attempts, so far, have been woefully ineffective. You can get reasonably efficient transfer over a few meters, and you can get some transfer over longer distances, but nothing close to what is needed. Even under the best of circumstances, the microwave energy density called for at the Earth surface is less than that of sunshine, so what is the point?

  • Eniac February 17, 2012, 20:24

    What’s the point of sending embryos to another star system? Why would people do that?

    The main reason would be to assure a colony of a reasonably sized gene pool at nanograms rather than 100-200 kg per genome. Also, frozen embryos do not eat, drink or breathe, and they will not go nuts and blow up the ship.

  • Rob Henry February 17, 2012, 22:00

    Eniac, the question is not if the power satellites have a few technical difficulties, its if they have far fewer than practical fusion or not.

    If they do, I may even have to move my mining operation. Earths crust has about 10ppm Th and 3ppm U, does anyone know this compares with Mercury?

  • Ole Burde February 18, 2012, 5:02

    “You can get reasonably efficient transfer over a few METERS, and you can get some transfer over longer distances, but nothing close to what is needed. Even under the best of circumstances, the microwave energy density called for at the Earth surface is less than that of sunshine, so what is the point? ”
    Try googling ” 1975 goldstone experiment” ….82% efficiency over 1.5 mile.
    The real reason no further progress has been made is probably political related to th word RADIATION , if and when the military will want a transmission system , it will be capable of bypassing the radiation scare by making the hole thing classified ! Perhabs it already has !

  • Tobias Holbrook February 18, 2012, 8:31

    “Terraformer, the potential gravitational energy of those moons really does look enticing now that you mention it. Can you think of a way to tap it rapidly that does not take too massive an infrastructure?”
    Nothing that doesn’t involve an orbital ring system and space elevators, no. Or maybe a system of momentum exchange tethers to pass material from the moons to the surface at a high efficiency of conversion. If it’s a double planet or tidal locked system like Pluto-Charon or Orcas-Vanth, it should be possible to build a bridge between the two and just use that to decelerate mass on to the primary. Alas, I can’t claim credit for the idea – I got it from karov (on NewMars) and he got it from Paul Birch.

    Of course, if you’re Proteroforming the body (giving it a thick, non-toxic, warm atmosphere), you can dump the heat into the body by impacting small bodies directly. I thinkNyx and Hydra each have enough kinetic energy to vaporise and heat a small Nitrogen atmosphere (0.1-1 bars). Certainly, one would have to disassemble them to terraform Pluto, but that’s not much of a loss…

    Hopefully, binary sysems will be sufficiently common that slow accretion of the two bodies via a space bridge will be able to provide sufficient energy to sustain a civilisation for millenia, and if they’re not tidal locked… maybe we could tap their rotation for energy? If such bodies are differentiated, they may have subsurface oceans that can be colonised, and maybe even cores that are enriched enough in elements such as Uranium and Thorium for nuclear reactors to be made (for spacecraft, probably). Certainly, it means getting at metals will be easier, and we won’t have to heat them up to melt the water.

    I think we’re looking, then, at binary systems with differentiated bodies and ideally a subsurface ocean in one of the bodies, with a significant size difference between the two, if we are to viably colonise interstellar space without the use of fusion. If we have fusion, of course, all bets are off…

  • Eniac February 18, 2012, 13:04

    @Rob: The real question is whether solar power satellites will ever be competitive with regular terrestrial energy sources, never mind fusion.

    For example, when you compare SPS with ground solar, in order to utilize the space vs. ground advantage in insolation, the product of transmission efficiency and cost ratio needs to be >10%, which to me is practically inconceivable. Also, there is the issue of land area for the rectenna. If the power density is larger than solar, you have to worry about frying the wildlife. If it is lower, you might as well build a solar farm. I am not sure I see much of a sweet spot in this particular trade-off.

    @Ole: 82% of the energy that actually impinged on the rectenna. Not of the energy that was used to produce the beam. There is a reason that all you get googling this is one video. Anyone caring enough to check the facts apparently changed their mind before celebrating this enormous breakthrough, which it would be if true as advertised.

  • Eniac February 18, 2012, 13:59

    The Goldstone experiment is a great example of a myth being kept alive because of wishful thinking. You have to search really hard to get at the truth, because the “82% efficiency” meme is just so much more compelling. Here is a fragment that gets us closer, from someone who should know, posted by Jordin Kare in an on-line forum:

    Jordin Kare:

    Thanks for the mention. One small correction: The 1975 Goldstone microwave experiment had a *receiver* efficiency of 82%; the end-to-end efficiency was much lower. The highest demonstrated end-to-end efficiency at the time was 54%, in a much smaller laboratory experiment. See, e.g., W. C. Brown, “The history of wireless power transmission,” Solar Energy Volume 56, Issue 1, January 1996, Pages 3-21. (Many sources erroneously quote the 82% figure as the overall efficiency, so you are not alone)


    I have yet to find any account of the actual full path efficiency of that experiment, my estimate is it would have been around 5%. The experiments of Brown with the end-to-end 57% percent that Jordin refers to here extend over just a few meters, and were what I was referring to in mentioning short range results.

    The reason there is so little work and so few reliable results is not to be sought in politics or conspiracy theories, but rather in the simple fact that efficient long range wireless power transmission is a technological non-starter. One fairly reliable sign to recognize such “technologies” by is when they cite Nicola Tesla among their pioneers :-)

  • Max February 18, 2012, 14:10

    Again, what’s the point in sending embroys out to colonize a star system? Why would people do that? I can understand that some people may want to move to another star system if conditions there are right and rapid interstellar travel is both practical and cheap. But sending out “seed material”? Why would a society do that? What’s the gain for those who embark on such a venture? It makes no sense.

  • Eniac February 18, 2012, 14:54


    So it seems that I was not the only one who was surprised when I first found out that typical levels of uranium and thorium are at least 1000 times higher in the Earth’s crust than meteorites.

    Upon further research, it appears that contrary to my intuition, Uranium is highly enriched in the Earth’s crust, from about 0.008 ppm to 1-2 ppm, for various reasons. So, this one of your premises appears to be valid. See:

  • Ole Burde February 18, 2012, 16:15

    It seems that nothing of any real importance has been done in microwave transmission since the goldstone experiment in 1975 !
    Here and there in the landscape of technology , are strange ” black holes” or “white areas on the map” , of which almost nothing is known … even if they could be extreemly important in several variations of the future.
    Another such “terra incognitu” is the gigantic continent of artificial closed ecosystems , which might be the future of intensive agriculture in space AND on earth . Nothing has happened since the seventies .
    A possible explanation that has been sugested ,is that public funding for technology resaerch is decided by a bunch of blind monkeys poking on a typewriter . Personally I believe its a bit extreeme.

  • Eniac February 18, 2012, 17:14

    @Max: What we have been talking about here mostly is to send embryos WITH the colonists, not by themselves. To fortify the gene pool at minimal expense. This makes enormous sense, once you accept the motivation for going at all.

    As for sending a seed, only, you are correct that the motive has to be entirely selfless. I will not venture to explain to you why this might be a good idea. It does happen, though. Ask any tree, sea turtle or other creature that goes to enormous trouble just to spread its seeds. Or, any parent who paid $200,000 in college tuition.

  • Ole Burde February 19, 2012, 9:20

    It seems that you were right about the Goldstone experiment , and that I didnt dig deep enough .
    Does this mean microwave transmision is a non-starter ? perhabs , but if this branch of tecnology can be written off after a single experiment in 1975 , then almost anything difficult could be given up , which are not emediately profitable for private industry or the military .
    Powerproduction in space on a big scale is a necesary building block in any plan to advance space activities in general , including for sailpowered missions inside 50 years from now . It is still very temptating to imagine the sale of electricity to earth as a way of financing the bigger picture …even if one might have to pay lipservice to a lot of green brain polution .

  • Eniac February 20, 2012, 9:21


    if this branch of tecnology can be written off after a single experiment in 1975 , then almost anything difficult could be given up

    It is not quite like that. There were more experiments, before and after, plus a lot of theoretical research. What is rare is positive results. This is why hyped mischaracterizations like the 82% of Goldstone stand out so much. SPS advocates are a determined bunch, and they will grasp at straws.

    I would also like to qualify my own assertion a little. I think terrestrial applications are technological and economical non-starters, but in space, things might be different. Also, with the advent of efficient lasers (FEL or diode), there might be reason to look again into power transmission by light. 10-20% overall efficiency appear possible, and in some applications that may be useful. There has been research into this in connection with the space elevator, which requires power beaming in its most realistic incarnations.

  • Rob Henry February 21, 2012, 3:25

    I was interested in doing back of the envelope figures for extractable orbital energy for moons of Oort cloud objects as suggested by Tobias Holbrook. I also looked at Pluto sized bodies and Hydra sized moons in Hydra scaled orbits (radius 65 000km). Unlike Tobias (who gave atmospheric gas volume that could be generated) I expressed my results in cumulative number of human lives that could be supported. I assumed a hundred year life expectancy and a 10kW energy requirement. The most obvious comparison is that the Earth has so to date managed to support about 30 billion humans (though estimates vary).

    I found that the results depend on the rotation rate of the dwarf planet compared to the moon. If that dwarf planet was spinning faster than the moon orbited it could support just a 100 million human lifetimes by sending that planet off to infinity, but if its spin was slower we could bring it to that planets surface with the release of about 10 billion human lifetimes of energy.

    These were unspectacular figures, considering that these would be the very largest bodies that we might find in the Oort Cloud. Then suddenly it came to me. If these bodies had undifferentiated interiors, then the formation of a core would release about 100,000 times that energy. Does anyone know of a way to harness this?

  • Tobias Holbrook February 21, 2012, 14:08

    Unspectacular figures? Maybe not compared the the theoretical maximum carrying capacity of Terra, Mars, or even Ceres, but looking at the total number of bodies in the Oort cloud… also, I wasn’t just talking about Nyx and Hydra, but Charon too. How much energy could be generated by the slow coalescence of the two bodies via a space bridge?

    You’re talking about releasing the gravitational potential energy of a body. Hmmm, you’d have to melting the entire thing, probably… and aren’t bodies over 10km already most likely differentiated? On the plus side, that heat might still be around, in the form of a molten core, and in the light gravity of the dwarf planets, tapping it would be a lot easier.

  • Eniac February 21, 2012, 16:42


    It occurred to me that you could, in principle, always just bring two or more separate bodies together to eventually harvest the entire energy freed up by putting them in each other’s gravity well. That should be good for a LOT of lives…

    One way to do is would be to apply small course correction to one body to bring it close to another in such a way that there is near zero angular momentum between them. Then, use a long compressive strut to both tie them together and keep them apart. Gradually shorten and widen the strut while having the approaching bodies perform work on an electromechanical generator. There will be a point of maximum force for the strut to support, until the centrifugal force from the remaining angular momentum takes over. The final state is two bodies in close orbit, with the strut removed to be reused on the next pair of bodies.

    Actually, I think “zero angular momentum” implies a collision course, and we could harvest any velocity difference as kinetic energy in addition to the gravitational energy. Obviously neither can be too big, given material strength constraints, but much can be done with a proper choice of bodies and trajectories. You could have the bodies almost collide, tether them together at closest pass, collect enough kinetic energy as the tether is reeled out to capture the bodies gravitationally, then use the strut to collect all of the gravitational energy.

  • Rob Henry February 21, 2012, 21:02

    Tobias, I had imagined that there is no way to extract energy from a system that entirely consists on two bodies in complete tidal lock, but your plan seems so cunning that you could stick a tail on it and call it a weasel! The most obvious thing that it relies upon is that the transport of a small mass from one to the other over your bridge is so efficiently effected that more electricity is generated lowering it from the neutral point to Pluto than is taken in raising it to that point from Charon. From what I have read of the potential for a space elevator, that seems possible. Even if energy neutral, it will break tidal lock and allow other mechanisms.

    For my estimate of the double dwarf planet coalescence energy I will retain Charon’s place and mass, but alter its density to that of Pluto. Both Pluto and Charon will have undifferentiated interiors, and they will combine to form a body of uniform density.

    Actually I won’t give detailed results, save that to take all Charon’s mass to Pluto’s surface consumes more energy than it produces (the kinetic energy of rotating once every half hour greatly exceeds gravitational binding energy). You must also be moving mass from Charon’s dark side to infinity to counter the effect of conservation of angular momentum. Or perhaps you are actually equilibrating the masses of Pluto and Charon rather than coalescing them as advertised. I could eventually work out the optimum myself, but my calculations would be greatly speeded if you could give me more details. I fear that you plan might just be too cunning to work!

  • Rob Henry February 21, 2012, 21:13

    Eniac, for the system to have zero angular momentum as a whole does not mean that both orbital and rotational components of it are zero, only that their combined sum is. Thus you scheme looks far better.

    Actually if we are to plan to capture one body, why not try capturing two simultaneously. This not only provides easier ways to capture, but also easier ways to cancel angular momentum.

    Finally we have the energy to support the quadrillions of human lifetimes that I so desire. Many thanks!

  • Torbjörn Larsson, OM February 22, 2012, 15:42

    before the target is reached.

    That is planet centric. If a colonization reaches its Oort cloud it is on “an interstellar trip”.

    The Oort objects are far much resource concentrated and less riskier than the rare planets deep down their risky, expensive gravity wells. They have solids for habitats, volatiles for biospheres and fissiles for energy.

    These objects are movable too with volatiles for rocket engines, thus obviating the need for more expensive crafts. All what a colonization would need to seed the vast galaxy.

    That scenario is not as dramatic as a starship journey

    On an exponential scale fitting our resource growth, the Oort clouds is the largest step, even larger than going to the moon. (There is an xkcd comic on that.) The stars are little extra effort after that.

  • Eniac February 22, 2012, 15:47


    No matter what the sources of angular momentum are, once you manage to bring two bodies onto a near-collision course, you can easily fine tune the trajectory to completely cancel all angular momentum, I think. If there is no rotation, the zero angular momentum solution is a head-on collision. With rotation, an offset needs to be introduced. Well, you need a little bit of an offset in any case, as a true head on collision is not really that useful…

    I don’t really see a reason to make this more complicated than a two-body problem.

    Rotation introduces some more structural demands: you would have to construct a track around the equator of any rotating body in order to mechanically couple orbital and rotational angular momentum. Have the “bridge” run on the tracks, then apply the brakes. Generative brakes, of course. Once you have tidal lock, you can take the tracks to the next project and start compressing the bridge. If your original aim was good, you should be able to bring the bodies almost to where they touch before they spin out of control.

    You invest a small push, just enough to bring to carefully selected bodies onto a collision course, potentially a long time later. You harvest: 1) The kinetic energy of the asymptotic velocity difference between the bodies (using the capture tether), 2) the kinetic energy from the differential angular momentum (using the equatorial tracks), and 3) The gravitaional energy of coalescence (using the compression bridge). If you decide to do numbers on this, I would be very interested in them. It seems to me that we have a viable solution here. Until, that is, the entire Kuiper belt is lumped into a sparse disk of large rubble piles. Time to move on to the Oort cloud…

  • Torbjörn Larsson, OM February 22, 2012, 16:01

    I now note Joy’s comment on fissiles. They are based on the curious notion of comets as all ice bodies, yet with meteoritic levels of fissiles. In reality, these bodies are a mix that we don’t know much about. Some will not be suitable as habitats et cetera.

    No, there are no ores in plate tectonics less planetary system bodies. What you want are differentiated, core building, bodies. Those are larger than ~ 100 km, and their heavier elements, including U, are concentrated to the core.

  • Eniac February 22, 2012, 19:34


    …, and their heavier elements, including U, are concentrated to the core.

    Well, not necessarily. See above…
    (and here: http://world-nuclear.org/info/inf78.html)

  • Steven Rappolee February 23, 2012, 20:34

    Many of you enjoy talking about Fusion verses Fission starship engines
    I recently dug up the email address’s for the director of the national ignition facility an emailed him with my community college student idea that we have plenty of helium 3 right here on earth!
    Here is my plan to sell to you :)

    A future starship it is discovered must be in the realm of the economics of the civilization that builds it and this means that helium 3 is in fact all around us on earth and most likely everywhere else in the solar system, its Lithium that is used in thermal nuclear weapons mainly the Teller–Ulam and layer cake designs.
    (Fission-fusion-fission yields HE3 from lithium)
    I suggested Teller–Ulam micro capsules last year to the national ignition facility for testing or at least computer simulation testing as the prospects of igniting lithium with a thin layer of fissile material on the micro capsules outer shell in the the NIF test chamber must have brought on some fear and loathing, but I wonder? With the NIF powerful lasers and/X-ray derived source who would need the fissile outer shell in a lithium micro capsule? Or in an in space engine who would care about a fissile outer shell far removed from our planets biosphere?

    I did receive a response from the NIF public relations director but I can’t find any content in his response :)I cannot discern if he agrees or is in horror with the idea of a Teller-Ulam micro-capsule experiment in the NIF test chamber, but when I suggested the computer simulation of this idea, he did respond to that email with a suggestion that my community college adviser help me file a request with his office of research………………………
    Check mate!
    It’s not likely there is anyone at my community college would have the expertise to to help me with NIF grant writing idea but some of you out there do.

    I have a prediction, an Icarus Interstellar fusion engine could utilize the proposed Teller–Ulam micro-capsules with a lower kilohertz cycle but with a larger burst of energy per cycle thus we would have a pusher plate needed for the fusion engine :) or a hybrid daedalus
    Icarus starship engine.

  • ljk February 24, 2012, 2:44

    The Standford news press release on the nomad worlds here:


    To quote:

    If observations confirm the estimate, this new class of celestial objects will affect current theories of planet formation and could change our understanding of the origin and abundance of life.

    “If any of these nomad planets are big enough to have a thick atmosphere, they could have trapped enough heat for bacterial life to exist,” said Louis Strigari, leader of the team that reported the result in a paper submitted to the Monthly Notices of the Royal Astronomical Society. Although nomad planets don’t bask in the warmth of a star, they may generate heat through internal radioactive decay and tectonic activity.

    Searches over the past two decades have identified more than 500 planets outside our solar system, almost all of which orbit stars. Last year, researchers detected about a dozen nomad planets, using a technique called gravitational microlensing, which looks for stars whose light is momentarily refocused by the gravity of passing planets.

    The research produced evidence that roughly two nomads exist for every typical, so-called main-sequence star in our galaxy. The new study estimates that nomads may be up to 50,000 times more common than that.

  • ljk February 24, 2012, 3:03

    “Nomad’ Planets Could Outnumber Stars 100,000 to 1

    by Nancy Atkinson on February 23, 2012

    Could the number of wandering planets in our galaxy – planets not orbiting a sun — be more than the amount of stars in the Milky Way? Free-floating planets have been predicted to exist for quite some time and just last year, in May 2011, several orphan worlds were finally detected.

    But now, the latest research concludes there could be 100,000 times more free-floating planets in the Milky Way than stars. Even though the author of the study, Louis Strigari from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), called the amount “an astronomical number,” he said the math is sound.

    “Even though this is a large number, it is actually consistent with how much mass is in our galaxy and heavy elements we have our galaxy,” Strigari told Universe Today. “So even though it sounds like a big number, it puts into perspective that there could be a lot more planets and other ‘junk’ out in our galaxy than we know of at this stage.”

    And by the way, these latest findings certainly do not lend any credence to the theory of a wandering planet named Nibiru.

    Several studies have suggested that our galaxy could perhaps be swarming with billions of these wandering “nomad” planets, and the research that actually found a dozen or so of these objects in 2011 used microlensing to identify Jupiter-sized orphan worlds between 10,000 and 20,000 light-years away.

    That research concluded that based on the number of planets identified and the area studied, they estimated that there could literally be hundreds of billions of these lone planets roaming our galaxy….literally twice as many planets as there are stars.

    But the new study from Kavli estimates that lost, homeless worlds may be up to 50,000 times more common than that.

    Full article here:


  • Eniac February 25, 2012, 2:15

    I think that would mean that the closest Nomad planets are expected to be only around 0.1 light year away (dividing the distance to AC by the 3rd root of 50,000). If we could detect them, somehow, we could send an interstellar mission to visit several of them.

    Detection will not be easy, though, I suspect.

  • Rob Henry February 26, 2012, 6:43

    Eniac, the total energy extractable from gradually gravitationally coalescing the Kuiper belt is vast. As you have already pointed out, there are ways to cancel angular momentum, and this would make the theoretical extractable energy close to the gravitational binding energy difference less the components original binding energy. You, and others, have also convinced me that there are so many different ways to extract this energy that I have concluded it useless to pick one and just assumed the processes are 50% efficient. The only point of difference is that I still hold that capturing bodies in pair is preferable, even if I grant that mechanically coupling one at a time to energy generation is a useful simplification.

    From Wikipedia the mass of the Kuiper belt is between 0.04 and 0.1 Earth masses, and assuming a density of 1.5 times water, the gravitational binding energy of the combined body should be between 0.7 and 3 million trillion trillion joules. Even if the original material was all objects Pluto’s size, we would just have to subtract 14% to 8% from those figures respectively, and now assuming 50% power generating efficiency the equivalent human lifetimes supported as figured above is 10 to 45 quadrillion.

    The Oort Cloud has far more mass, but it is so much more diffuse that it seems unwise to second guess the plans of any sector of it.

  • Rob Henry February 26, 2012, 17:57

    I feel that I should have added a few details to my model for those who wish to play with Oort Cloud figures and scenarios, or who wish to assume that there will be more than one kingdom formed it the Kuiper Belt.

    Firstly the figure that I gave for the original binding energy as a proportion of the final was a deliberate gross overestimate, and given how small that turned out to be can be neglected (although if your kingdoms are too numerous that is no longer the case, and I should derive a new figure from the power law that has been experimentally determined for the Kuiper belt)

    Secondly, fixing the density (at 1500 in SI units) makes binding energy proportional to the 5/3 power of mass, so if you figure in kingdoms of y% each of an Earth mass, then the number of quadrillion 100yr 10kW human lifetimes supported at 50% efficiency by each is 1.1 * y^(5/3)

  • ljk February 29, 2012, 12:00

    Will all those nomad exoworlds actually be of benefit to our getting from one star system to another?


  • Keith Pretzer November 27, 2012, 1:26

    Imagine a technological civilization orbiting a super-Jovian nomad. They gather CHON material and water from the clouds. Dropping cables from their habitats they generate electricity as the orbiting lines transit the nomad’s magnetic field. Heavier elements and metals may be scarce unless there are satellites orbiting the nomad that can be cannibalized. The drive to maintain a technological base would be strong as without it they perish. Masters of recycling and carbon nanofacturing, they might maintain records going back a million years. Whenever they pass another nomad planet, they in turn “swarm” and colonize the new object. As they pass near other stars, they may have records of other life and civilizations. There’s rich material here for a science fiction story, robust with technological and sociological speculations.