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Re: Colony Integration of alternatives to Space Elevator Systems

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  • Eric Hunting
    It s possible that one could create consortiums of private equity as you describe. The question is if this could ever be enough for projects of such great
    Message 1 of 15 , Feb 1, 2008
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      It's possible that one could create consortiums of private equity as
      you describe. The question is if this could ever be enough for
      projects of such great scale and if there's any actual motivation
      among the people involved to do it.

      Looking at national economic statistics is misleading because they
      don't usually mean what they seem to imply. When we see a figure as
      you noted for dollar 'value' for a national economy, it's not
      measuring any sort of stockpile of capital. When an economist declares
      that the US has a 14.5 trillion dollar economy, that's a measure of
      the volume of money that is flowing through the economy. It's a
      measure of the economic 'bandwidth' of the nation as a function of how
      many dollars change hands per year, which implies the scale of
      commerce conducted here. That money doesn't actually exist as some
      stockpile of cash anywhere or under any particular individual or group
      of people's control so that someone can use it as equity. That money
      is like the number of bits on the Internet.

      What makes more sense is the volume of reserve capital, but this isn't
      as easy to quantify since, technically, there isn't any in any long-
      term sense. Money doesn't sit still anywhere on the globe. Beyond the
      money people put in savings accounts, it is constantly circulating the
      global economy through innumerable investment instruments in search of
      every penny in profit it can eek-out. When someone invests in one
      thing, they are usually liquidating something else in order to do it.
      Some of this is invested for the long-haul, some is being 'parked'
      while it looks for something better, and some of it is being traded
      day-to-day. So one has a question of the 'intent' of money in the
      system as well as its basic volume, which is really very difficult to
      quantify.

      To figure out what economic scale of things is most likely feasible to
      do today it makes sense to consider examples of what has already been
      done recently; the largest of current government and commercial
      projects. Wars, of course, top the list because governments tend to
      abandon even the pretense of fiscal responsibility when addressing
      them. Military systems and facilities projects closely follow in
      fiscal delusion. Here many trillions are routinely spent by many
      nations, but only because it can be rationalized in terms of 'national
      defense' according to how fearful, insecure, world-ignorant, and
      xenophobic the national culture and how meddlesome the geopolitical
      policy. As the self-appointed Pointy Haired Boss of Earth Inc., the US
      spends inordinately on this. After this come government programs that
      basically just disburse funds on a large scale spread over some long
      time. Again, this can deal in trillions but over spans of decades.
      Governments feel comfortable spending so much on such programs because
      politicians can argue that, per-year per-taxpayer, they don't really
      cost all that much.

      Looking at more specific public works projects, the Apollo program was
      the largest, most expensive, and most concerted of specific space
      projects to date (the Soviet counterpart having been abandoned before
      completion) but it was actually a relatively minor program, compared
      to the money that gets thrown at the military in the US today.
      Adjusted for inflation, Apollo cost 135 billion dollars by the time
      the plug was pulled. How much have we now spent on Iraq? The
      International Space Station is a joint project of 5 national space
      agencies with NASA and Roskosmos dominating. It is estimated to cost
      about 130 billion dollars upon completion in 2011, with something like
      56 billion being contributed by NASA. We don't typically think of the
      ISS as being on par with Apollo in accomplishment, but, ironically, it
      is in cost and time spent. After this come municipal construction
      projects. Kansai International Airport -built on an enormous built-up
      island- cost 20 billion dollars to construct over 7 years. It may be
      the biggest airport project to date. The Big Dig in Boston was the
      largest individual municipal construction project in US history. It
      cost 14.6 billion dollars when completed in 2004. In comparison, the
      Hoover Dam cost under 700 million adjusted for inflation. The Channel
      Tunnel was the biggest of such projects in Europe at a cost of 12
      billion dollars. (clearly, there's a productivity gap here in the US
      if Europeans can cross the English channel for 12 billion over 7 years
      and Americans have to spend nearly 15 billion and 20 years just to get
      across Boston -though to be fair the Big Dig supposedly hired top
      European talent and technology) China's Three Gorges Dam, which won't
      actually be completed until 2011, has an estimated cost of 22.5
      billion over 17 years. The 57km long Gothard Base Tunnel in
      Switzerland, part of the AlpTransit under-the-Alps base tunnel project
      will be the current longest railway tunnel in the world when completed
      in 2017 and is expected to cost about 6.5 billion over its 24 years of
      construction. Combined with its smaller 34.6km Lotcshberg tunnel,
      total cost of the AlpTransit complex and associated railways is
      anticipated to be about 24.4 billion, which may put it at the top of
      world municipal construction projects. The biggest planned municipal
      project in the world at the moment may be the Dongtan Eco-City project
      near Shanghai. A complex of three villages with a total area 3/4th the
      size of Manhattan, it is slated to be completed by 2040 with the first
      village completed by 2010 and will supposedly be a totally sustainable
      and self-powered city exclusively using electric and human-powered
      vehicles and renewable energy. It's not clear how much this will cost
      in terms of government and municipal investment at this point. It's
      supposed to be part of Shanghai's Expo 2010, the latest in the
      seemingly abandoned and forgotten tradition of Worlds Fairs.

      Commercial projects seem to top out at a comparable scale to municipal
      construction projects. Multinational corporations have frequently
      engaged in 100 billion dollar deals, usually buying each other out,
      but these aren't cash transactions or simply financed. They are
      exchanges of complex collections of equity and credit. The biggest
      specific commercial projects involving the development of some machine
      like an aircraft, ship, or rocket or some building like a skyscraper
      or luxury resort seem to have all been under 5 billion dollars. The
      biggest resort project to date was the Atlantis Resort at one billion -
      though this may have been superseded more recently by projects in
      Dubai. The Taipei 101 skyscraper cost 1.8 billion dollars to build.
      The anticipated Burj Dubai (the next tallest skyscraper in the world)
      is slated to cost over 4 billion dollars. Collectively, the
      outrageously extravagant 'New Downtown' district of Dubai has cost, so
      far, about 20 billion.

      So, with the exception of war follies and death toys, the most
      expensive projects to date done by government or commercial interests
      don't really come very close to the guestimated costs of many of these
      proposed giant space project concepts like the Space Pier. Maybe such
      sources of investment can do better than they have to date. But we
      can't really expect them to go radically farther in the near future
      than they have in recent times. And this doesn't really address the
      question of why one would invest in such projects even if they could.
      Apollo had the most concerted national social support of any space
      project in history and yet, as we can see, it didn't actually win much
      more financial support than todays ISS, which is lucky to get an
      occasional footnote in the news.

      Why would anyone invest anything in space? What, where, and when is
      the return on investment? Satellites, of course, are a known quantity
      in terms of their markets and the cost of their deployment. The cost
      of their deployment by conventional rockets is 'nominal' relative to
      their return on investment -though this may not always be the case.
      Satellite technology is under increasing competition from the
      terrestrial telecom infrastructure and, as a branch of the Internet
      infrastructure, it just plain sucks because of latency issues. Space
      tourism, now getting a lot of attention, is still a variation of the
      known business of tourism, even if in this form one is depending on
      unproven transportation and structural technology and its potential
      return on investment is speculative. (which is why it hasn't yet seen
      anything close to the same scale of investment routinely put into
      tourism) But beyond this, what? One cannot consider transportation
      technology outside of the context of what it's transporting.
      Transportation systems do not generate profit by themselves. They are
      only communications devices. As I was recently writing on the TMP2
      site, this is why the railway barons of the turn of the 19th century
      could not consider rail development independent of the industrial and
      community development that supplied rail with traffic and were the
      source of its revenue. So they had to think about the whole natural
      resource and real estate development package. They had to figure out
      how to create the destinations and the traffic for their rail empires
      as if they were a completely integral part of them, So, if we were
      going to build something like the Space Pier tomorrow, what would we
      do with it? You have you're cheap access to space, now what? What is
      there in space that you can use to pay for the huge cost of creating
      this access to space, and can you get enough return on investment from
      it to not just get investment but get investment despite the risk of
      entirely unproven technology?

      This is the single greatest obstacle to the development of space. The
      launch costs that everyone in space advocacy today obsesses over over
      mean nothing. You could have a near-zero launch cost technology right
      now and you still would not be able to raise the money to build a
      system on a greater scale than what already exists because there's
      nothing in space to pay for it with. There are a lot of nebulous ideas
      about making money in space, but all of them are speculation. Nothing
      has really been demonstrated and proven beyond the telecom satellite,
      and, while you can make good money at that, there is no dramatic
      growth in that industry and none anticipated in the near future. Cheap
      launches and cheap satellites can't solve the problem of latency.

      This is why, in TMP2, the Asgard phase starts with the Modular
      Unmanned Orbital Laboratory. It's job is to solve this near-term
      problem by doing the industrial R&D that leads to figuring out what
      you can make in space that has some high value and how to make it. But
      this is only a stop-gap. This only helps you get to the point of an
      early orbital industrial infrastructure supported by a modest
      transportation infrastructure. Long-term, that same problem of return
      on investment persists because no means of space transportation now
      proposed may be sufficiently cheap that you can go and get stuff from
      asteroids, turn it into cars and dishwashers on Mars or the Moon, and
      then send them to Earth to sell at a competitive price compared to
      those same things made on Earth from Earth's own resources. (the only
      transit technology that can hope to even come close to that would be a
      very large and well developed series of space elevators, assuming most
      of their construction and materials comes from space) Making things
      cost-effectively in space for import to Earth will only be practical
      for a relatively small spectrum of very compact and very high value
      products -most likely akin to such things as computer chips.

      Ultimately, the big ROI from space is only realizable for those people
      who intend to spend it out there. No one willingly moved to the New
      World with the intent to stay there permanently until they were able
      to figure out how to transpose the Old World models of the 'good
      life' in this New World environment. They had no models for the good
      life in the context of what was then considered a 'godforsaken savage
      wilderness'. So they just kept going back to or importing everything
      from the Old World once they had made it rich until it became possible
      to replicate wholesale the aspects of European upper-class living in
      (and in-spite of) the New World environment. That took a long period
      of time developing a very sophisticated industrial infrastructure in
      the New World to pull it off. Some would argue America never did
      really give-up parroting Europe. (which used to piss-off the likes of
      Frank Lloyd Wright no-end because he thought Americans should have
      figured out some superior and uniquely American model of the good life
      by at least the start of the 20th century. That was the premise of his
      whole architectural career) So the only investment that will chase
      that ROI in space is going to come from those people who actually want
      to go to space to live and who have the imagination to visualize some
      kind of good life out there and the process of how to make it. Today,
      this is an extremely small portion of the population and not a
      particularly wealthy one. Indeed, most people in space advocacy -
      including people in this very forum- could not describe to you what
      the good life in space is like. They aren't concerned about what it's
      like to live there. They're just obsessed with the issue of getting
      there at all, which is fine but doesn't pay the bills when not very
      many people share that obsession. The bottom line of all economics is
      'incentives'. When the long-term ROI in space can only be realized in
      space, you have to have this very clear compelling and attractive
      model for how you intend to actualize it there and all NASA has ever
      shown us of what living in space is like is variations on the theme of
      submarine duty! Now you know why space has long been such a hard sell
      to the society at large. If you want the mainstream public to be
      sustainably interested in space and get large volumes of investment in
      it, you have to show them how much better their life is going to be
      there. You have to show them how to live like princes on orbit and
      explain in excruciating and plausible detail how you make that happen.
      No one in space advocacy has ever done this and only a few futurists
      have even tried. When was the last time you ever saw a mock-up of a
      house in space?

      This is why Marshal Savage was so keen on the issue of cultivating a
      new culture. He understood that, because the ROI in space could only
      be actualized in space, he needed to create a society with the
      cultural model for how to live well there and thus the mass cultural
      incentive to throw money, resources, and effort at it for a very long
      time. This is also why Aquarius was so important to this cultural
      cultivation. He needed a place to experiment with and demonstrate some
      of the characteristics of life in space and showcase them as something
      superior to living in Levittown or Brooklyn. And he also needed a
      place with some degree of isolation where he could cultivate a society
      of means and surplus productivity that could be invested in space. A
      society that isn't getting all its productivity squandered on crap
      like endless wars, throw-away automobiles, diamond-studded Hello Kitty
      junk, and the usury of casual debt as it routinely is in the western
      industrial nations.

      Of course, none of this is going to suit the needs of someone who
      thinks the world is going to end tomorrow and is looking for Spaceship
      Earth's ejector seat. I'm sorry, but that's not very likely to be
      found anywhere in any particular launch system concept barring some
      miraculous spontaneous breakthroughs in a very large spectrum of
      technology. One's best hope there is to get insanely rich, move to
      Dubai, invest every penny you can in AI, and coerce as many of your
      neighbors as you can to do likewise.

      Eric Hunting
      erichunting@...



      On Jan 30, 2008, at 9:03 AM, Luf-team@yahoogroups.com wrote:

      > Re: Colony Integration of alternatives to Space Elevator Systems

      > Posted by: "Bill Haught" wlhaught@...
      > autumnofburnoutcommie67Tue Jan 29, 2008 6:42 pm (PST)
      > But I'm skeptical of concepts that call for the up-front
      > > construction of complex gigantic megastructures that would take
      > > several decades at best to create today and yet can't actually do
      > > anything useful until they're completed.
      >
      > Couldn't several private equity and sovereign wealth funds back a
      > project
      > and sell bonds?
      >
      > Couldn't construction start in several places along the route?
      >
      > I'll agree that it would need to be done quickly, even given todays
      > low
      > long-term rates and high inflation.
      >
      > America (or what used to be America) alone has a $14.5 trillion
      > economy.
      >
      > > Certainly, if
      > > one could get the whole of human society motivated toward a common
      > > goal one could accomplish Big Things very quickly. But we live in an
      > > increasingly demassified global society. Not only was this next to
      > > impossible without the threat of war to motivate it in the past,
      > it's
      > > going to be increasingly harder in the future because people in the
      > > future will have increasingly divergent interests and increasing
      > > independence from any centralized resource, industrial, and economic
      > > infrastructures and thus any centralized political and bureaucratic
      > > authority. The fabric of human society is balkanizing.
      >
      > What about 2008 AmeriKKKa which getting a lot like 1936 Germany? Are
      > you
      > aware of the work (every job applicant in America must have his/her
      > eligibility to work verified by the DHS, using the error-plagued
      > Employment
      > Eligibility Verification System (EEVS)) and the no-gun lists ? The
      > current
      > crop of candidates aren't about to allow that to happen. Zoning laws
      > stand
      > in the way of affordable non-toxic housing as I'm sure you are aware
      > of.
      > Where I live in Cuyahoga County, Ohio there is a city ironically
      > called
      > Independence that doesn't allow unrelated people to live in the same
      > house.
      > There are no apartments in the city. Oh, and the houses must be at
      > least
      > 2,000 sq. ft. Independence only for those that can afford it, I
      > guess. The
      > minimum wage has dropped to roughly half of what it was in 1968.
      > When you
      > factor in demographics (aging of the workfarce) the flat wages
      > becomes a
      > steep decline. How do you move forward with low wages and costly
      > health
      > care, housing, and transportation?
      >
      > ACLU Raises Concerns on Senate Immigration Bill; Proposed
      > Legislation Would
      > Harm Privacy, Due Process
      > http://www.aclu.org/immigrants/gen/29878prs20070525.html
      >
      > I don't have a good link on H.R. 2640 since I'm not sure what is
      > accurate.
      > At a minimum, a psychiatrist can put you on a no-gun list. I'm not
      > sure if
      > that is can or must or if the government can get you there by other
      > means.
      >
      > > Most oppression and war throughout history
      > > has its roots in the concentration of social and economic power
      > within
      > > an upper class with a chronic predisposition to psychopathy.
      >
      > (Clearing throat) What do you think we have now? Haven't you noticed
      > the
      > proxy wars with Russia and China in the Middle East? Are you aware
      > of how
      > much it has cost us already? Is what I'm proposing that much more
      > expensive?
      >
      > Cost of Iraq war could surpass $1 trillion: Estimates vary, but all
      > agree
      > price is far higher than initially expected by By Martin Wolk
      > http://www.msnbc.msn.com/id/11880954/
      >
      > > We can
      > > look forward to a future where there are virtually no institutional
      > > concentrations of economic and political power, where national
      > > identities become about as relevant as sports team affinity, and
      > thus
      > > war and oppression will be much reduced in incidence, duration, and
      > > scale. But it also means that accomplishing anything that requires
      > > some kind of collectivization of resources and mass mobilization
      > will
      > > require the cultivation of cultural memes to inspire it. There won't
      > > be this marching at the end of a bayonet (so to speak) nonsense as
      > > we've had for centuries nor any tyranny of democratic opinion when
      > > everyone has the option to 'take their ball and go home'.
      >
      > Again same reply as above. When Shillary or
      > Rudolph-the-red-faced-Rottweiler gets in she/he will have the power
      > of a
      > dictator thanks to all of the laws passed under Bush and Dubya's
      > signing
      > statements allowing him to disregard any laws he damn well pleases.
      >
      > Back to top
      > Reply to sender | Reply to group | Reply via web post
      > Messages in this topic (8)
    • Eric Hunting
      I agree that rotovator concepts have a definite near-term advantage in that they are doable with existing materials and can easily be experimented with using
      Message 2 of 15 , Feb 2, 2008
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        I agree that rotovator concepts have a definite near-term advantage in
        that they are doable with existing materials and can easily be
        experimented with using systems of small scale. And they certainly
        have a powerful advantage in the orbital transfer role, as I've
        already noted on the TMP2 site. But I don't see how they're really a
        whole lot simpler when dealing with so many new technologies and
        developing at least two and possibly three completely new
        transportation systems to use it. Easier near-term than a space
        elevator? Maybe. Easier than developing a reusable rocket like the
        SeaStar? I have my doubts.

        To develop a rotovator system you have to develop at least two
        different transportation systems; the rotovator itself and the launch
        system that delivers and collects payloads from it. The deployment
        launch system might employ existing commercial launch systems as long
        as the initial rotovator system is kept within the payload capacity of
        current launch systems. Though this is doable without new material
        like nanofiber, it doesn't necessarily mean that there's going to be a
        lot of payload fraction in the tether system itself, especially when
        some of that fraction must be used for conductors and insulators to
        allow for electrodynamic propulsion. Systems I've read about suggest a
        24,000kg package carried on a Delta IV or the Space Shuttle for an
        initial rotovator system but only a 2500kg payload capacity for it.
        That's certainly a useful capacity, but only 1/10 the whole mass of
        what's considered a minimum deployed system. So a high payload
        capacity may mean a very large amount of initial launch mass or many
        launches of modular components by other means, though the individual
        tether is not likely to be launched in pieces and is 5 times the
        payload capacity of one deployed system by itself. Some design
        concepts seem to treat the entire anchor and tether system as a single
        modular unit, growing by attaching multiples together in a side-linked
        cluster. This is a simple approach to incremental growth. But with the
        above example of the 24,000kg modular system package, it would take
        ten of them deployed just to carry one of them. That would be quite an
        elaborate piece of hardware. I can't imagine this sort of structure
        ever getting bigger or more complex than that -at least for a rotating
        momentum exchange system. So the system can't build or maintain
        itself. It may always be dependent upon another big conventional
        rocket to maintain it.

        The suborbital shuttle that carries payloads to and from the tether
        end would tend to be a rather exotic vehicle if designed to be
        reusable. Most concepts call for some form of hypersonic sub-orbital
        space plane that's rocket or hybrid propelled that can fly at a
        sustained speed of around mach 12 at a 100km altitude. There's nothing
        like this currently in existence and it's something that has defied
        aerospace development programs spending billions for the past 40
        years. So this isn't trivial. SpaceShip One got to that altitude but
        only broke mach 3 for a relatively short period of time -and it still
        needed a carrier plane. SpaceShip Two is just bigger, not better in
        performance. Payload transfers would not be simple by any stretch of
        the imagination. When was the last time any two planes did mid-air
        refueling at supersonic speeds? A non-reusable rocket that discards a
        propulsion stage on connection is a much easier to engineer prospect
        but would still be pretty sophisticated to perform this job, needing
        long duration variable vectorable thrust -mostly likely something
        based on aerospike engine technology. But at that rate one could just
        as well move the whole rotovator to a higher LEO position and use a
        rocket based LEO launch system, just treating the rotovator as a LEO
        to GTO system. That is probably a whole lot simpler than trying to
        make a hybrid hypersonic aircraft and snagging and detaching payloads
        at mach 12 in the atmosphere. I have absolutely no problem with that
        idea. Like I said, it's already in TMP2. I consider that a perfectly
        logical precursor to space elevator development.

        But is this somehow better than a space elevator? You still can't
        eliminate the need for heavy lift capability initially for either of
        these systems. In fact, the SE is more demanding at first because it
        has to get its initial hardware to GEO. (with a LEO rotovator one of
        the more practical ways to do that) But an SE ultimately eliminates
        the need for heavy lift capability after a certain stage of growth
        because it can reduce the increments of its expansion to a very small
        scale it can carry on its own (eventually, its laminator/fabricators
        might be pulling carbon right out of the atmosphere) and apply them
        directly to the existing tether structure. And I don't understand what
        is supposed to be 'magical' about laser power. Lasers exist. They
        aren't SciFi. We know how to make them to the necessary scale to power
        something across that distance. We even know how to use a UV laser
        beam as a virtual wire in atmosphere, exciting air molecules to become
        conductive without needing the sort of voltage that will make a plasma
        out of it. And once an SE is big enough it can conduct power
        internally as a big microwave or optical duct. A rotovator is not
        likely to do better than just barely match the payload capacity of the
        heavy lift system that built it. And unless handling two-way traffic,
        it can only loft one payload per months because it must spend the rest
        of its time correcting its orbit for the next trip. An SE has no limit
        on the volume of payload it may ultimately carry and, though initially
        limited to treks taking weeks, would ultimately be moving goods and
        people on an hourly basis.

        One could make a strong argument that a rotovator transfer system is
        much more sensible at the small scale than an SE, especially
        considering the high potential failure rates from micrometeorid
        strikes and the high cost of launching that long a tether in one
        piece. And so an SE might be a better prospect when one can really do
        it much as Arthur C. Clarke described; fabricating it on orbit and
        lowering a large structure whole with a very high initial carrying
        capacity. But long term, it doesn't seem to me to be a contest. The
        rotovator is easier only for as long as it takes to start mass
        producing unlimited length nanofiber. Once that's at-hand, nanofiber
        becomes the default material for making either of these kinds of
        systems. That's just a matter of time and at that point the SE becomes
        just the more convenient version of a rotovator. Given how much time
        it would take to develop a hybrid hypersonic transport plane to
        support an in-atmosphere transfer rotovator if we started today (I
        would assume a decade at best, given that this has stymied the general
        deep-pocketed aerospace industry for 40 years) it's a very close race.
        However, a LEO-GTO rotovator is definitely a much better prospect
        since it's eliminating the in-atmosphere transfer and could be done
        today using existing vehicle systems.

        Of course, I have serious doubts that we in the LUF would be able to
        achieve our own access to that within a decade, so it's still a close
        race. Anything we talk about now as something TMP might do in space
        is, at the very least, a decade off. This stuff is way beyond casual
        community projects. We're talking a lot more sophisticated engineering
        and industrial capability than doing a co-housing project based on T-
        slot and static float platforms. Indeed, not one person in this forum
        has built his own sounding rocket system or even so much as his own
        RepRap -though I'm considering it. (I have a T-slot based Dobsonian
        and recumbent bike in the works first...oh, and maybe a 'cowboy hot-
        tub'; a hot tub design that combines the coiled tube and basket type
        burner of the DutchTub with a large steel horse trough, I think that
        would really sell in this southwest area, though since I can't handle
        the wood smoke myself, I need to devise some sort of bottled gas
        fixture)

        Eric Hunting
        erichunting@...



        On Jan 30, 2008, at 9:03 AM, Luf-team@yahoogroups.com wrote:

        > Re: Colony Integration of alternatives to Space Elevator Systems

        > Posted by: "ben lipkowitz" fenn@... mow4212345Tue Jan
        > 29, 2008 10:16 pm (PST)
        > I've been reading about rotating tethers and they seem like a great
        > idea -
        > I also wonder why all the fuss about space elevators. Rotovators are
        > not
        > "competitive" with the space elevator - they blow it out of the water!
        > There's no reason to go chasing the space elevator when we can build
        > rotovators NOW using real and inexpensive materials, with less
        > complexity,
        > cost, and transit time than a space elevator. They can be upgraded
        > incrementally (and in fact this capability is necessary since the
        > redundant lines will be periodically cut by micrometeroids) so there
        > is no
        > waste or downtime. The grappling problem is not that hard - you fire a
        > grapple line from your vehicle such that it crosses the tether at an
        > angle, then the two lines wrap around each other and hooks catch at
        > the end as they slide apart.
        >
        > Less complexity because you dont have a huge magic laser at the
        > bottom..
        > The momentum is recovered with solar power and lorentz force - how
        > could
        > it get any simpler? Another way to recover momentum is to de-orbit an
        > incoming payload. The concept is beautiful. The reason the beanstalk
        > space
        > elevator has caught on and become so widely known is because it is
        > such a
        > powerful symbol, not because it is at all practical or optimal.
        >
        > The 3km/s and 100km altitude rendezvous point is within the range of
        > 'DIY'
        > spacecraft like spaceship two. Interested yet? A two-tier tether would
        > mass as little as 5-30x the payload, excluding the counterweight
        > mass. The
        > original tether lines and counterweight could be launched piecemeal
        > with a
        > "light gas gun" or jordin kare's modular laser launch system. In
        > fact you
        > could launch the payloads directly from a light gas gun to the end
        > of the
        > tether in reusable cargo pods.
        >
        > Isn't it funny that we need a long piece of string to "tie it all
        > together"?
        >
        > For a technical introduction to tethers this paper is pretty cool:
        > http://www.tethers.com/papers/HASTOLAIAAPaper.pdf
        >
        > this is a nice graphic explaining electrodynamic propulsion:
        > http://www.tethers.com/EDTethers.html
        >
        > @Bill: you could theoretically make a rotovator that reached all the
        > way
        > down to the earth at standstill, but it would have to be spinning much
        > faster and thus you would need stronger materials than are currently
        > available to counteract the centrifugal force. (although not _that_
        > much
        > stronger, mind you.) such things are possible right now on mars and
        > luna,
        > by using spectra, graphite fiber, or kevlar tethers. at least they
        > would
        > be if we had any way of getting there. the tower would be unnecessary
        > because the rotor comes down almost perfectly vertical, and what's
        > another
        > 10km on a 1000km tether? The atmosphere only presents a heating
        > problem
        > when it's moving at hypersonic speeds relative to the tether.
        >
        > Multiple tethers can be used for orbital transfer and rapid transit
        > throughout the solar system with no propellant or energy expenditure -
        > provided you have traffic going both ways.
        >
        > I should have brought this topic up earlier, thanks for reminding me!
        >
        > -fenn
      • Bill Haught
        First off, it may be better to integrate some of this stuff in your blog or wikis (or refer to them if it is there) than spend quite so much time on your
        Message 3 of 15 , Feb 2, 2008
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          First off, it may be better to integrate some of this stuff in your blog or
          wikis (or refer to them if it is there) than spend quite so much time on
          your posts. Regardless of its validity, Peak Oil, Peak Food, etc are all
          over the net.


          > Looking at national economic statistics is misleading because they
          > don't usually mean what they seem to imply. When we see a figure as
          > you noted for dollar 'value' for a national economy, it's not
          > measuring any sort of stockpile of capital. When an economist declares
          > that the US has a 14.5 trillion dollar economy, that's a measure of
          > the volume of money that is flowing through the economy. It's a
          > measure of the economic 'bandwidth' of the nation as a function of how
          > many dollars change hands per year, which implies the scale of
          > commerce conducted here. That money doesn't actually exist as some
          > stockpile of cash anywhere or under any particular individual or group
          > of people's control so that someone can use it as equity. That money
          > is like the number of bits on the Internet.

          I'd rather look at industrial capacity, which can be/is a small portion of
          GDP.


          > To figure out what economic scale of things is most likely feasible to
          > do today it makes sense to consider examples of what has already been
          > done recently; the largest of current government and commercial
          > projects. Wars, of course, top the list because governments tend to
          > abandon even the pretense of fiscal responsibility when addressing
          > them. Military systems and facilities projects closely follow in
          > fiscal delusion. Here many trillions are routinely spent by many
          > nations, but only because it can be rationalized in terms of 'national
          > defense' according to how fearful, insecure, world-ignorant, and
          > xenophobic the national culture and how meddlesome the geopolitical
          > policy. As the self-appointed Pointy Haired Boss of Earth Inc., the US
          > spends inordinately on this. After this come government programs that
          > basically just disburse funds on a large scale spread over some long
          > time. Again, this can deal in trillions but over spans of decades.
          > Governments feel comfortable spending so much on such programs because
          > politicians can argue that, per-year per-taxpayer, they don't really
          > cost all that much.

          Somehow we need to get around this. If your ideas are sufficient to prevent
          a Malthusian crash and can be implimented here on Earth , that is one way,
          by avoiding the need for big corporatism and big government altogether.
          Then too, the same things standing in the way of your ideas stand in the way
          of mine.


          Regarding big corporate infrastructure investments, what about the oil
          platforms in the oceans? Doesn't that top out at around $20 billion?

          > Why would anyone invest anything in space? What, where, and when is
          > the return on investment?

          > Space
          > tourism, now getting a lot of attention, is still a variation of the
          > known business of tourism, even if in this form one is depending on
          > unproven transportation and structural technology and its potential
          > return on investment is speculative. (which is why it hasn't yet seen
          > anything close to the same scale of investment routinely put into
          > tourism) But beyond this, what? One cannot consider transportation
          > technology outside of the context of what it's transporting.
          > Transportation systems do not generate profit by themselves.

          > So, if we were
          > going to build something like the Space Pier tomorrow, what would we
          > do with it? You have you're cheap access to space, now what? What is
          > there in space that you can use to pay for the huge cost of creating
          > this access to space, and can you get enough return on investment from
          > it to not just get investment but get investment despite the risk of
          > entirely unproven technology?
          >

          I am thinking of making systems to support the infrastructure for
          space-based solar power and beaming the power to towers above most or all of
          Earth's water vapor. Perhaps the Space Pier can double for other uses of
          tall towers.

          > no means of space transportation now
          > proposed may be sufficiently cheap that you can go and get stuff
          > fromasteroids, turn it into cars and dishwashers on Mars or the
          > Moon, and then send them to Earth to sell at a competitive
          > price compared to those same things made on Earth from
          > Earth's own resources

          Well, don't send asteroid material in and out of gravity wells? Granted, we
          send stuff back and forth between nations too much. Globalization would
          work better if instead of the third factor of production (rent--n. land and
          natural resources) being stolen by the sword and "divine" "right" hundreds
          of years ago and rolled into capital people got checks from a world
          equivalent of the Alaska Permanent Fund and fossil fuel was not so cheap.

          What about moving bulk material and goods with magnetically driven systems
          or tethers and m2p2? What may be needed is an integrated system of
          transportation.


          > Ultimately, the big ROI from space is only realizable for those people
          > who intend to spend it out there. No one willingly moved to the New
          > World with the intent to stay there permanently until they were able
          > to figure out how to transpose the Old World models of the 'good
          > life' in this New World environment. They had no models for the good
          > life in the context of what was then considered a 'godforsaken savage
          > wilderness'. So they just kept going back to or importing everything
          > from the Old World once they had made it rich until it became possible
          > to replicate wholesale the aspects of European upper-class living in
          > (and in-spite of) the New World environment. That took a long period
          > of time developing a very sophisticated industrial infrastructure in
          > the New World to pull it off.

          The reason I want importing from Earth to be as cheap as possible. We could
          move infrastructure needed to build infrastructure, and the people too.


          > When the long-term ROI in space can only be realized in
          > space, you have to have this very clear compelling and attractive
          > model for how you intend to actualize it there and all NASA has ever
          > shown us of what living in space is like is variations on the theme of
          > submarine duty!

          I'm thinking of a large spinning station, like Babylon 5. My own suite in
          it with about 2000 sq ft of very usuable space--shelving for walls, etc.,
          lots of plants in pots, and good paying jobs. Even just that little would
          be great, better than what I have now. Any extra dough I'd probably invest
          in the space economy, at least initially.

          Now you know why space has long been such a hard sell
          > to the society at large. If you want the mainstream public to be
          > sustainably interested in space and get large volumes of investment in
          > it, you have to show them how much better their life is going to be
          > there.

          If they can sustainably sustain their current lifestyle for 25 hour weeks
          and actually save for retirement that would be a great improvement. Perhaps
          technology can solve the aging problem, but that is another story. Also,
          not everyone has the living standard of lower-middle class Americans, if
          there is still such a class in America today.


          > This is why Marshal Savage was so keen on the issue of cultivating a
          > new culture. He understood that, because the ROI in space could only
          > be actualized in space, he needed to create a society with the
          > cultural model for how to live well there and thus the mass cultural
          > incentive to throw money, resources, and effort at it for a very long
          > time. This is also why Aquarius was so important to this cultural
          > cultivation. He needed a place to experiment with and demonstrate some
          > of the characteristics of life in space and showcase them as something
          > superior to living in Levittown or Brooklyn. And he also needed a
          > place with some degree of isolation where he could cultivate a society
          > of means and surplus productivity that could be invested in space. A
          > society that isn't getting all its productivity squandered on crap
          > like endless wars, throw-away automobiles, diamond-studded Hello Kitty
          > junk, and the usury of casual debt as it routinely is in the western
          > industrial nations.

          Are you saying it is that hard to find people who'd like to live in
          alternative communities? Cultists have no problem finding potential
          victims.
        • ben lipkowitz
          Eric, There seem to be some misunderstandings in your comparison of rotovator vs beanstalks. 1) The reason for the mach 12 number is the specific strength of
          Message 4 of 15 , Feb 4, 2008
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            Eric,

            There seem to be some misunderstandings in your comparison of
            rotovator vs beanstalks.

            1) The reason for the mach 12 number is the specific strength of available
            materials. When carbon nanotubes become available, the rotovator will be
            able to 'touch down' on the surface of the earth at zero relative
            velocity.

            It's not required that the payload transfer take place in or near the
            atmosphere, that was just the subject of the Boeing study.


            2) You dont have to use electrodynamic propulsion to recover the momentum
            used to boost payloads. This can also be accomplished by reeling the
            tether in and out at perigee and apogee, like on a swingset, which
            increases the eccentricity of the orbit. However, tether reeling doesn't
            affect the overall angular momentum, and so you would need other ways to
            recover lost velocity due to atmospheric drag. I got the impression that
            the conductor would weigh very little as it would only run a few km of the
            tether. For aluminum, 10km long by 1mm diameter is only 21 kg. Also, the
            conductor doesn't "use up" the available payload mass, since you're really
            just adding more to the counterweight.

            Over time, a large enough tether such as a beanstalk space elevator would
            clear out all the particles in the Van Allen belts, making electrodynamic
            propulsion impossible. I can already hear the ham radio operators
            grumbling.

            3) 1/10 payload fraction seems pretty good to me! In the papers i've read
            it's more like 1/30, which also seems pretty good. What is the payload
            mass fraction of a beanstalk space elevator? A 747? A diesel locomotive
            and 1000 km of track? Does it really matter? If the destination is the
            tether counterweight, you increase the payload capacity of the whole
            system by that fraction every launch without expending any other effort.
            This is an exponential increase.

            The payload does not need to fit existing launch systems - the reduction
            in delta-V to orbit means you can launch more payload and less fuel. If
            chopping out the unused section of fuel tank costs more than not chopping
            it out, well, that's not the rotovator's fault.

            4) How is treating the entire system as a single unit "modular" at all?
            The main reason for a complete single-launch operational system is so they
            can start making money with it immediately, instead of waiting around for
            on-orbit assembly and bootstrapping. It's not necessarily the best way to
            do it from an engineering perspective. You wouldn't launch a beanstalk in
            one piece either. If one particular proposal does it that way, it doesn't
            mean incremental assembly is impossible. Why do you say incremental
            assembly is unlikely?

            5) "months" to reboost? For the 2500kg payload, assuming our counterweight
            is mostly solar panels, (what else?) at a conservative 1kW/20kg for each
            solar panel times 1000 panels, to recoup 30MJ/kg(payload) of momentum
            would take less than a day. (2500*30000/1000 = 75000sec.) This calculation
            isn't totally realistic but puts us in the ballpark. If electrodynamic
            propulsion doesn't work for some reason, there's still plenty of other
            high specific impulse propulsion technologies to choose from.

            I hope I can respond to your other concerns but it's past my bedtime now.
            -fenn

            PS: You dont need to pull up the top end of a ribbon with a plasma thuster
            - it pulls itself up due to tidal forces. Google "gravity gradient" for
            more info.

            PPS: there is quite a lot of interesting reading material here, especially
            under 'Exotic':
            http://yarchive.net/space/

            > Posted by: "Eric Hunting" erichunting@... erichunting2001
            > Date: Sat Feb 2, 2008 9:06 am ((PST))
            >
            > I agree that rotovator concepts have a definite near-term advantage in
            > that they are doable with existing materials and can easily be
            > experimented with using systems of small scale. And they certainly
            > have a powerful advantage in the orbital transfer role, as I've
            > already noted on the TMP2 site. But I don't see how they're really a
            > whole lot simpler when dealing with so many new technologies and
            > developing at least two and possibly three completely new
            > transportation systems to use it. Easier near-term than a space
            > elevator? Maybe. Easier than developing a reusable rocket like the
            > SeaStar? I have my doubts.
            >
            > To develop a rotovator system you have to develop at least two
            > different transportation systems; the rotovator itself and the launch
            > system that delivers and collects payloads from it. The deployment
            > launch system might employ existing commercial launch systems as long
            > as the initial rotovator system is kept within the payload capacity of
            > current launch systems. Though this is doable without new material
            > like nanofiber, it doesn't necessarily mean that there's going to be a
            > lot of payload fraction in the tether system itself, especially when
            > some of that fraction must be used for conductors and insulators to
            > allow for electrodynamic propulsion. Systems I've read about suggest a
            > 24,000kg package carried on a Delta IV or the Space Shuttle for an
            > initial rotovator system but only a 2500kg payload capacity for it.
            > That's certainly a useful capacity, but only 1/10 the whole mass of
            > what's considered a minimum deployed system. So a high payload
            > capacity may mean a very large amount of initial launch mass or many
            > launches of modular components by other means, though the individual
            > tether is not likely to be launched in pieces and is 5 times the
            > payload capacity of one deployed system by itself. Some design
            > concepts seem to treat the entire anchor and tether system as a single
            > modular unit, growing by attaching multiples together in a side-linked
            > cluster. This is a simple approach to incremental growth. But with the
            > above example of the 24,000kg modular system package, it would take
            > ten of them deployed just to carry one of them. That would be quite an
            > elaborate piece of hardware. I can't imagine this sort of structure
            > ever getting bigger or more complex than that -at least for a rotating
            > momentum exchange system. So the system can't build or maintain
            > itself. It may always be dependent upon another big conventional
            > rocket to maintain it.
            >
            > The suborbital shuttle that carries payloads to and from the tether
            > end would tend to be a rather exotic vehicle if designed to be
            > reusable. Most concepts call for some form of hypersonic sub-orbital
            > space plane that's rocket or hybrid propelled that can fly at a
            > sustained speed of around mach 12 at a 100km altitude. There's nothing
            > like this currently in existence and it's something that has defied
            > aerospace development programs spending billions for the past 40
            > years. So this isn't trivial. SpaceShip One got to that altitude but
            > only broke mach 3 for a relatively short period of time -and it still
            > needed a carrier plane. SpaceShip Two is just bigger, not better in
            > performance. Payload transfers would not be simple by any stretch of
            > the imagination. When was the last time any two planes did mid-air
            > refueling at supersonic speeds? A non-reusable rocket that discards a
            > propulsion stage on connection is a much easier to engineer prospect
            > but would still be pretty sophisticated to perform this job, needing
            > long duration variable vectorable thrust -mostly likely something
            > based on aerospike engine technology. But at that rate one could just
            > as well move the whole rotovator to a higher LEO position and use a
            > rocket based LEO launch system, just treating the rotovator as a LEO
            > to GTO system. That is probably a whole lot simpler than trying to
            > make a hybrid hypersonic aircraft and snagging and detaching payloads
            > at mach 12 in the atmosphere. I have absolutely no problem with that
            > idea. Like I said, it's already in TMP2. I consider that a perfectly
            > logical precursor to space elevator development.
            >
            > But is this somehow better than a space elevator? You still can't
            > eliminate the need for heavy lift capability initially for either of
            > these systems. In fact, the SE is more demanding at first because it
            > has to get its initial hardware to GEO. (with a LEO rotovator one of
            > the more practical ways to do that) But an SE ultimately eliminates
            > the need for heavy lift capability after a certain stage of growth
            > because it can reduce the increments of its expansion to a very small
            > scale it can carry on its own (eventually, its laminator/fabricators
            > might be pulling carbon right out of the atmosphere) and apply them
            > directly to the existing tether structure. And I don't understand what
            > is supposed to be 'magical' about laser power. Lasers exist. They
            > aren't SciFi. We know how to make them to the necessary scale to power
            > something across that distance. We even know how to use a UV laser
            > beam as a virtual wire in atmosphere, exciting air molecules to become
            > conductive without needing the sort of voltage that will make a plasma
            > out of it. And once an SE is big enough it can conduct power
            > internally as a big microwave or optical duct. A rotovator is not
            > likely to do better than just barely match the payload capacity of the
            > heavy lift system that built it. And unless handling two-way traffic,
            > it can only loft one payload per months because it must spend the rest
            > of its time correcting its orbit for the next trip. An SE has no limit
            > on the volume of payload it may ultimately carry and, though initially
            > limited to treks taking weeks, would ultimately be moving goods and
            > people on an hourly basis.
            >
            > One could make a strong argument that a rotovator transfer system is
            > much more sensible at the small scale than an SE, especially
            > considering the high potential failure rates from micrometeorid
            > strikes and the high cost of launching that long a tether in one
            > piece. And so an SE might be a better prospect when one can really do
            > it much as Arthur C. Clarke described; fabricating it on orbit and
            > lowering a large structure whole with a very high initial carrying
            > capacity. But long term, it doesn't seem to me to be a contest. The
            > rotovator is easier only for as long as it takes to start mass
            > producing unlimited length nanofiber. Once that's at-hand, nanofiber
            > becomes the default material for making either of these kinds of
            > systems. That's just a matter of time and at that point the SE becomes
            > just the more convenient version of a rotovator. Given how much time
            > it would take to develop a hybrid hypersonic transport plane to
            > support an in-atmosphere transfer rotovator if we started today (I
            > would assume a decade at best, given that this has stymied the general
            > deep-pocketed aerospace industry for 40 years) it's a very close race.
            > However, a LEO-GTO rotovator is definitely a much better prospect
            > since it's eliminating the in-atmosphere transfer and could be done
            > today using existing vehicle systems.
            >
            > Of course, I have serious doubts that we in the LUF would be able to
            > achieve our own access to that within a decade, so it's still a close
            > race. Anything we talk about now as something TMP might do in space
            > is, at the very least, a decade off. This stuff is way beyond casual
            > community projects. We're talking a lot more sophisticated engineering
            > and industrial capability than doing a co-housing project based on T-
            > slot and static float platforms. Indeed, not one person in this forum
            > has built his own sounding rocket system or even so much as his own
            > RepRap -though I'm considering it. (I have a T-slot based Dobsonian
            > and recumbent bike in the works first...oh, and maybe a 'cowboy hot-
            > tub'; a hot tub design that combines the coiled tube and basket type
            > burner of the DutchTub with a large steel horse trough, I think that
            > would really sell in this southwest area, though since I can't handle
            > the wood smoke myself, I need to devise some sort of bottled gas
            > fixture)
            >
            > Eric Hunting
            > erichunting@...
            >
            >
            >
          • Eric Hunting
            Concerning item one, the tip speed for a rotovator is not a product of the tether material strength and how far to the ground it goes. It s determined by the
            Message 5 of 15 , Feb 14, 2008
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              Concerning item one, the tip speed for a rotovator is not a product of
              the tether material strength and how far to the ground it goes. It's
              determined by the orbit it is centered on. That speed is the speed of
              LEO relative to the surface of the earth. (this varies, but a lot of
              concepts put it in orbits at that speed) To negate that speed and
              still sit in LEO a momentum exchange rotovator would have to rotate
              relative to its orbit at a speed that gives its tip a negative
              relative velocity at its lowest point equal to its orbital velocity.
              So it 'walks' around its orbit and where the tether touches down it
              has zero horizontal velocity, but only for the second or less its at
              its lowest point. It would touch-down at the same set of points
              repeatedly. This is where the nanofiber comes in. To achieve that
              relative velocity the system must tolerate tremendous centrifugal
              force. But if you have that material at-hand, a momentum exchange
              rotovator makes less sense for ground-to-orbit transit than a a space
              elevator -unless you're using it to assist building an SE.

              If a non-momentum-exchange or 'skyhook' type rotovator were to achieve
              a zero tip velocity relative to the ground it can only do it by being
              in GEO. It is then, in effect, the exact same thing as a 'space
              elevator' or 'beanstalk'.

              This gets confusing because the term 'rotovator' is commonly being
              used to describe three different types of systems -skyhook rotovators
              which are always vertical relative the ground, momentum exchange
              rotovators which rotate relative to the ground, and beanstalks or
              space elevators which are just skyhooks in GEO- based on the premise
              that all of them are technically rotating about their center of
              gravity, just at different rates.

              On item two, I agree with you that a rotovator doesn't have to use
              electrodynamic propulsion for momentum recovery. However, reeling a
              tether in and out repeatedly using a mechanical system is much more
              failure-prone and doesn't really save you any energy. Electrodynamic
              propulsion is just the more solid-state choice. Also, sweeping the
              high-energy particles from Earth orbit would not have any effect on
              how electrodynamic propulsion works because its working in conjunction
              with the Earth's magnetic field, not these particles.

              On item three, I agree entirely that a 1/10th payload fraction can
              indeed be useful. I've often suggested that one can do more with the
              payload capacity of an Apollo capsule than NASA commonly does with the
              Shuttle's vast capacity if one is clever enough. My point is that if
              it takes the carrying capacity of 10 rotovator modules to lift the
              mass of one of those modules, there's no way the rotovator can assist
              in its own construction until then -and by that time it's probably as
              big as it will ever get without becoming too complicated a structure.
              A separate heavy launch system must be employed to build and maintain
              the structure at a much higher cost-per-pound than the rotovator
              itself might offer. So you're still stuck with the rockets. All these
              systems have this limitation to some degree. The key is a structural
              system that keeps the payloads you build the structure with within the
              payload fraction of the structure at any stage of its growth. It might
              take a lot of trips, but you get the full benefits of your new transit
              system. The space elevator can potentially do that very early in its
              development because its tether can be fabricated in place in very tiny
              increments after one to a few initial small capacity tethers are
              deployed. It's a much tougher proposition for these other types of
              systems because they have to prefabricate and transport a tether whole
              and expand its structure in large unit multiples. It's sort of like
              the difference between building a house through large sectional
              modules that need a big truck and crane to install and a house based
              on a small scale kit-of-parts system where all the parts can be
              carried by a single person. Both can potentially produce a structure
              of any size and, of course, big modules produce a structure faster,
              but which is cheaper to start?

              On item four, much depends on the specific type of system. At the time
              I wrote that I was assuming the discussion was about a momentum
              exchange rotovator. That's a structure in constant relative motion
              with no mechanism for traversing the length of the tether. Unless you
              can easily bring it to a complete standstill (relatively speaking)
              periodically, you can't do much work on it at all and it's out of
              operation when its stopped. Given that, incremental expansion seems
              unlikely. The 'skyhook' type rotovator has more options, given a
              mechanism to traverse its tether length. It could potentially be
              expanded incrementally like a space elevator; expanded though laminate
              thickening of the tether and the installation of small modular parts
              to a counterweight structure. However, if it employs electrodynamic
              propulsion it's tether must start out with a complex physical
              structure that may preclude simple laminate expansion, limiting it to
              large unit module expansion. Most designs seem to employ that
              approach, if they are at all expandable. Usually this is only even
              considered when one can't design a single unit system package that has
              a target capacity of 5000kg -which is currently considered the
              commercially-useful minimum. Generally, long term expansion isn't a
              consideration in these designs because they don't link-up to any
              specific destination and LEO is not a place considered useful for
              large scale settlements or facilities. An SE is based on the idea of
              its GEO upstation as a permanent destination it directly links to. Or
              to put it another way, other rotovators are ferry systems for a
              general range of orbital locations. An SE is a bridge to a permanent
              port facility.

              On item five, I concede ignorance on this issue but the proposed
              rotovator concepts I've been reading about so far suggest a single use
              per month and I assumed this was due to the time to correct orbit, but
              may also have to do with projections on payload preparation. I've been
              relying mostly on the proposed projects of the TUI company as examples.

              Eric Hunting
              erichunting@...



              On Feb 4, 2008, at 12:49 PM, Luf-team@yahoogroups.com wrote:

              > Re: Colony Integration of alternatives to Space Elevator Systems
              > Posted by: "ben lipkowitz" fenn@... mow4212345Mon Feb
              > 4, 2008 7:51 am (PST)
              > Eric,
              >
              > There seem to be some misunderstandings in your comparison of
              > rotovator vs beanstalks.
              >
              > 1) The reason for the mach 12 number is the specific strength of
              > available
              > materials. When carbon nanotubes become available, the rotovator
              > will be
              > able to 'touch down' on the surface of the earth at zero relative
              > velocity.
              >
              > It's not required that the payload transfer take place in or near the
              > atmosphere, that was just the subject of the Boeing study.
              >
              > 2) You dont have to use electrodynamic propulsion to recover the
              > momentum
              > used to boost payloads. This can also be accomplished by reeling the
              > tether in and out at perigee and apogee, like on a swingset, which
              > increases the eccentricity of the orbit. However, tether reeling
              > doesn't
              > affect the overall angular momentum, and so you would need other
              > ways to
              > recover lost velocity due to atmospheric drag. I got the impression
              > that
              > the conductor would weigh very little as it would only run a few km
              > of the
              > tether. For aluminum, 10km long by 1mm diameter is only 21 kg. Also,
              > the
              > conductor doesn't "use up" the available payload mass, since you're
              > really
              > just adding more to the counterweight.
              >
              > Over time, a large enough tether such as a beanstalk space elevator
              > would
              > clear out all the particles in the Van Allen belts, making
              > electrodynamic
              > propulsion impossible. I can already hear the ham radio operators
              > grumbling.
              >
              > 3) 1/10 payload fraction seems pretty good to me! In the papers i've
              > read
              > it's more like 1/30, which also seems pretty good. What is the payload
              > mass fraction of a beanstalk space elevator? A 747? A diesel
              > locomotive
              > and 1000 km of track? Does it really matter? If the destination is the
              > tether counterweight, you increase the payload capacity of the whole
              > system by that fraction every launch without expending any other
              > effort.
              > This is an exponential increase.
              >
              > The payload does not need to fit existing launch systems - the
              > reduction
              > in delta-V to orbit means you can launch more payload and less fuel.
              > If
              > chopping out the unused section of fuel tank costs more than not
              > chopping
              > it out, well, that's not the rotovator's fault.
              >
              > 4) How is treating the entire system as a single unit "modular" at
              > all?
              > The main reason for a complete single-launch operational system is
              > so they
              > can start making money with it immediately, instead of waiting
              > around for
              > on-orbit assembly and bootstrapping. It's not necessarily the best
              > way to
              > do it from an engineering perspective. You wouldn't launch a
              > beanstalk in
              > one piece either. If one particular proposal does it that way, it
              > doesn't
              > mean incremental assembly is impossible. Why do you say incremental
              > assembly is unlikely?
              >
              > 5) "months" to reboost? For the 2500kg payload, assuming our
              > counterweight
              > is mostly solar panels, (what else?) at a conservative 1kW/20kg for
              > each
              > solar panel times 1000 panels, to recoup 30MJ/kg(payload) of momentum
              > would take less than a day. (2500*30000/1000 = 75000sec.) This
              > calculation
              > isn't totally realistic but puts us in the ballpark. If electrodynamic
              > propulsion doesn't work for some reason, there's still plenty of other
              > high specific impulse propulsion technologies to choose from.
              >
              > I hope I can respond to your other concerns but it's past my bedtime
              > now.
              > -fenn
              >
              > PS: You dont need to pull up the top end of a ribbon with a plasma
              > thuster
              > - it pulls itself up due to tidal forces. Google "gravity gradient"
              > for
              > more info.
              >
              > PPS: there is quite a lot of interesting reading material here,
              > especially
              > under 'Exotic':
              > http://yarchive.net/space/
            • ben lipkowitz
              ... I might have been misusing the terminology. These are all momentum exchange tethers: skyhook - vertical relative to planet bolo - rotating, in space
              Message 6 of 15 , Feb 14, 2008
              • 0 Attachment
                > If a non-momentum-exchange or 'skyhook' type rotovator were to achieve
                > a zero tip velocity relative to the ground it can only do it by being
                > in GEO. It is then, in effect, the exact same thing as a 'space
                > elevator' or 'beanstalk'.
                >
                > This gets confusing because the term 'rotovator' is commonly being
                > used to describe three different types of systems -skyhook rotovators
                > which are always vertical relative the ground, momentum exchange
                > rotovators which rotate relative to the ground, and beanstalks or
                > space elevators which are just skyhooks in GEO- based on the premise
                > that all of them are technically rotating about their center of
                > gravity, just at different rates.

                I might have been misusing the terminology. These are all momentum
                exchange tethers:

                skyhook - vertical relative to planet

                bolo - rotating, in space

                beanstalk - vertical relative to the planet, in synchronous orbit

                rotovator - rotating coplanar with orbital trajectory, zero tip velocity
                relative to planet

                "bolo" is nice and short. I'll try to use it when not specifically talking
                about interactions with objects at atmospheric velocities.

                >
                > On item two, I agree with you that a rotovator doesn't have to use
                > electrodynamic propulsion for momentum recovery. However, reeling a
                > tether in and out repeatedly using a mechanical system is much more
                > failure-prone and doesn't really save you any energy. Electrodynamic
                > propulsion is just the more solid-state choice. Also, sweeping the
                > high-energy particles from Earth orbit would not have any effect on how
                > electrodynamic propulsion works because its working in conjunction with
                > the Earth's magnetic field, not these particles.

                Ironically, electrodynamic propulsion is very much like vacuum tubes. You
                can't just send current down a wire to nowhere, there must be some return
                path. If that return path is another wire, the lorentz force cancels out
                and no motion occurs. The idea is to use the ionospheric plasma as the
                return path. So, you need an emitter and a collector, or "plasma
                contactors" in order to send a current through the plasma. These are
                basically just large metal grids. Since the lorentz force would be acting
                on the plasma as well, and the current is the same, the total momentum
                imparted to the plasma would be equal to that imparted to the spacecraft.
                So, it's not actually acting directly on the earth's iron core, it's only
                accelerating the plasma in the opposite direction. (I might be wrong about
                this.)

                I suppose if you had a large capacitor bank at the end of the wire, you
                could send current to "nowhere" and return it after having physically
                rotated 180 degrees, thus acting directly on the earth's magnetic field.

                > The key is a structural system that keeps the payloads you build the
                > structure with within the payload fraction of the structure at any stage
                > of its growth. It might take a lot of trips, but you get the full
                > benefits of your new transit system. The space elevator can potentially
                > do that very early in its development because its tether can be
                > fabricated in place in very tiny increments after one to a few initial
                > small capacity tethers are deployed.

                This is exactly what I'm saying.

                > It's a much tougher proposition for these other types of
                > systems because they have to prefabricate and transport a tether whole
                > and expand its structure in large unit multiples.

                Where do you get this idea from? If a beanstalk can be upgraded
                incrementally there is no reason a bolo cannot also be.

                > ...I was assuming the discussion was about a momentum
                > exchange rotovator. That's a structure in constant relative motion
                > with no mechanism for traversing the length of the tether. Unless you
                > can easily bring it to a complete standstill (relatively speaking)
                > periodically, you can't do much work on it at all and it's out of
                > operation when its stopped. Given that, incremental expansion seems
                > unlikely.

                Even in a two-tier rotovator, the bulk of the structure is in the section
                directly attached to the counterweight. The rotating "whip end" accounts
                for a very small fraction the system mass.

                The way to traverse a rotovator is the same as a beanstalk - drive rollers
                pinching the cable. A repair/upgrade robot would be under about 1/3 gee,
                so it would actually be less demanding than a beanstalk at low altitudes.
                You can change the orbital eccentricity to get the bottom end out of
                the atmosphere for maintenance and upgrades.

                With clever timing, a robot could theoretically be released from one end
                of the tether, orbit for a while, and then be captured at the other end.
                This could be useful for transfering payloads between the rotating
                segments of a two tier tether.

                Due to its great length, a beanstalk will have even more of a problem with
                orbital debris than a tether in low orbit. So, it must also be made as a
                redundant cross-linked tube, at least for parts of its length. Beanstalk
                proposals are either handwaving away this issue or unaware of its
                seriousness. If a 240 km long single strand tether "would suffer lethal
                impacts at the rate of 30 per year" then what about a 36000 km tether? At
                least a small orbiting tether can simply move out of the way of known
                large debris, rather than trying to do a hula-hoop maneuver around them.
                But this wouldn't do much good anyway since we can't see most of the
                debris out there.

                A better problem to fixate on is "how are we going to braid all these
                redundant cables together?"

                > The 'skyhook' type rotovator has more options, given a
                > mechanism to traverse its tether length. It could potentially be
                > expanded incrementally like a space elevator; expanded though laminate
                > thickening of the tether and the installation of small modular parts
                > to a counterweight structure.

                > However, if it employs electrodynamic propulsion it's tether must start
                > out with a complex physical structure that may preclude simple laminate
                > expansion, limiting it to large unit module expansion.

                The complex redundant structure is used because of orbital debris impacts.
                The electrodynamic propulsion system is comparatively simple - a wire,
                some electrodes, and a power source. I would argue that laminate expansion
                only works at very large sizes, if at all, regardless what type of orbit
                you choose. Laminations start out at milligrams per meter for a beanstalk.

                > Generally, long term expansion isn't a consideration in these designs
                > because they don't link-up to any specific destination and LEO is not a
                > place considered useful for large scale settlements or facilities. An SE
                > is based on the idea of its GEO upstation as a permanent destination it
                > directly links to.

                This is exactly the problem. NASA isn't considering ANY large scale
                settlements or facilities, not in low earth orbit, not in GEO, not
                anywhere. And who else is funding tether research?

                I dont see how GEO would be a better place to live or work than LEO. No
                atmospheric drag = more radiation, more debris, and also communications
                latency issues. The only reason to move there is "because that's where
                the space elevator goes." Imagine if you could only build a railroad due
                north, wouldn't that be silly? Fortunately with orbiting bolos we can
                change direction and altitude at will.

                There was a lot of talk about solar power satellites in GEO in the 70's,
                which was necessary to beam power back to antennae on earth. Back then,
                computer and communications technology wasn't nearly as sophisticated,
                requiring lots of people on orbit to construct the thing. Though for some
                reason they never considered building it in GEO from lunar materials?
                Instead it would have been assembled in low earth orbit from earth
                materials and then boosted up whole. I'm not sure how this relates to
                people in geosynchronous orbit either.

                Most large colony proposals I've seen are located in a solar orbit of some
                sort (at lagrange points) presumably so they can keep large mirrors
                pointed directly at the sun and also colinear with a rotating habitat. In
                earth orbit a large rotating habitat would be subject to forces from
                gyroscopic precession. I doubt that these forces alone make it worth going
                to L5.


                > On item five, I concede ignorance on this issue but the proposed
                > rotovator concepts I've been reading about so far suggest a single use
                > per month and I assumed this was due to the time to correct orbit, but
                > may also have to do with projections on payload preparation. I've been
                > relying mostly on the proposed projects of the TUI company as examples.

                My back of the napkin calculation is admittedly unrealistic, and I'd like
                to see a better analysis if you run across any.

                -fenn
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