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  • Eric Hunting
    Part 5 - Avalon: In the original TMP Avalon represents the first concerted effort towards extraterrestrial colonization with the location of the Moon chosen
    Message 1 of 1 , Mar 1 8:35 AM
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      Part 5 - Avalon:
      In the original TMP Avalon represents the first concerted effort
      towards extraterrestrial colonization with the location of the Moon
      chosen for its proximity and thus its immediate potential as part of a
      space based industrial infrastructure. I see planetary and lunar
      settlement as more concurrent activities with slightly lesser priority
      than orbital development because they present less economical sources
      of materials because of a higher transport overhead. However, the Moon
      suffers less from these problems than Mars or any other planets by
      virtue of low gravity and so is a logical choice for sooner settlement
      based on that. Now, there is today a certain conflict in space advocacy
      circles over whether the Moon or Mars offer the better choice of first
      colonization efforts. Proponents of an initial Mars colonization base
      their preference on the notion that Mars offers better prospects of
      sustainable settlement by offering a much broader spectrum of raw
      materials. The argument goes that one has all the ingredients for a
      true extension of civilization on Mars while the Moon is quite limited
      in its spectrum of raw materials and so any settlement there cannot be
      self-sustaining. This may be correct but overlooks the fact that no
      single location in space is economically sustainable because of the
      tremendous up-front cost of going there and setting up shop. Using
      current and near-term technology, one simply cannot settle anyplace in
      the solar system without incurring some kind of tremendous debt that
      must be paid with whatever resources one can exploit in space.

      Unfortunately, planetary and lunar sources of materials are inferior to
      asteroid sources because of the higher cost in their transport. And the
      gravity eliminates one of the key non-material resources one can
      exploit in space. So the economic potential of lunar and planetary
      settlements is a much tougher prospect. But these bodies do have some
      advantages. They offer generally larger spectrums of materials in
      closer proximity and lower settlement facilities construction costs
      thanks to at-hand resources with which settlements can be built. The
      lunar or planetary settlement thus has more materials closer at hand
      and so can collect and process them faster and will have a lower cost
      in the establishment of industrial facilities to process them. These
      settlements still face the problem of needing to process materials into
      a very highly refined form to overcome very high transit costs. And
      nothing they can make is going to be cheap enough to have a lot of
      value on an Earth market. But they can produce some goods more easily
      than they can be produced on orbit and deliver them to space locations
      at lower cost than they can be delivered from Earth. What this suggests
      is that the initial market -and therefore source of investment- for the
      lunar and planetary settlement is NOT Earth but rather the community of
      on-orbit settlements. After that start one must then cultivate a
      domestic market through industrial diversification -just like the
      Asgard pattern.

      A common premise of Lunar and Mars advocacy is the idea that
      exploratory outposts translate into permanent settlement. But,
      historically, this has rarely been the case because of the fact that
      exploratory outposts tend to have their choice of location based on the
      logistics of staged travel through the wilderness and thus often aren't
      in optimal locations for resource exploitation. Lunar and planetary
      exploration is even worse than this because initial landing sights are
      virtually random -chosen usually for statistical odds on the type of
      topography derived from orbital remote sensing data. Exploration is
      critically necessary. But manned exploration is clearly not
      cost-effective when it is so costly to begin with and obviously can
      only be temporary. Thus I anticipate a pattern of initial settlement
      that parallels the MUOL; tele-operated outposts focussed on the tasks
      of resource assessment followed by the tele-robotic construction of
      initial permanent settlements and resource utilization infrastructure.
      This work will largely be the province of the prospecting, mining, and
      raw materials processing segments of the Asgard industrial community
      with support from the Foundation CIC.

      To minimize costs initial robotic exploration and settlement would be
      based on a three-stage approach; a first wave consisting of the
      installation of a constellation of telecom and survey satellites
      followed a small wave of a few initial 'soft' landing vehicles (powered
      vertical landing vehicles) which establish an outpost by delivering an
      initial set of fully assembled robots and self-contained systems and
      then the third continuous support wave conducted by delivery of
      components by 'rough' landing vehicles ('rocket-chute' delivered
      air-bag cushioned containers) which are gathered and assembled on-site
      by the robots delivered in the first wave. Several classes of systems
      and robots would be used. Power, telecommunications, and
      'assembler/service' systems would dominate the self-contained systems
      and may take the form of individual lander vehicles. Robots would be
      organized into classes of payload collection and transport (pick-it-up
      trucks), outside construction, excavation and earth-moving, and
      exploration. A key type of robot in this stage would be the long range
      explorer; a self-mobile lab platform with communications systems suited
      to even direct-to-Earth links in emergencies. These would perform the
      bulk of survey activities, traveling long distances and deploying and
      maintaining a web of small self-contained telecom nodes which fan out
      from the initial outpost to provide multiply redundant telecom links
      for teleoperation. Even robots need some degree of shelter to maximize
      their duty life -especially the more critical and delicate
      multi-purpose units which are relied on for the repair and maintenance
      of the other systems. Landing vehicles would provide initial shelter
      but as the on-site-built volume of hardware increases other simple
      shelters in the form of pneumatic foam rigidized, alloy channel arch,
      or panelized space frame sheds or huts would be built from bulk
      delivered components. These structures need not provide for human life
      support but they do need to provide meteoroid shelter and a reduced
      dust environment for repair and assembly activities. The configuration
      of these robotic outposts would take the form of a cluster of initial
      landers and support structures with a predefined 'drop field' for
      equipment delivery surrounded by an expanding web of 'roads' defined by
      chains of telecom nodes, power generation stations, and service
      component caches.

      Once sites for permanent settlement and neighboring industrial/mining
      facilities are identified the initial settlement facilities would
      likely be established by telerobotic construction using the same types
      of systems used in the exploration but relocated to these new sites. As
      with the Asgard scheme, human habitation will be contingent upon issues
      of telecom latency and the scale of industries established, thus
      trading continuous local systems maintenance for large subsystem
      obsolescence. Cost efficiency demands that initial permanent settlement
      be based on the maximum use of at-hand indigenous resources requiring
      the lowest amount of processing to exploit. This means one thing;
      excavated habitats. Marshal Savage was thus quite correct in
      anticipating Avalon's founding on a kind of excavated habitat system.
      Where Savage diverges from practicality and his own community ideology,
      in my opinion, is in the notion of domed homesteads built into existing
      craters. The water shielded transparent membrane hull is again the
      sticking point. At the small scale of the individual homestead the
      degree of shielding by water is inadequate. At the large scale, once
      again you have the issue of water not being as transparent as
      anticipated at the kind of thickness where it would provide good
      radiation shielding. On top of that, in a gravity environment one must
      use high internal pressures to resist the water mass. This means the
      very large habitat must use additional structural layers to rigidize
      the dome without pushing the internal atmospheric pressure too high.
      This means more structural material and less transparency. The obvious
      solution is, again, the same kind of hull system proposed for the
      EvoHab. But this is still not as practical for the initial lunar or
      planetary settlement because of its high quotient of manufactured
      components which rely on refined alloys.

      But these locations offer a much more cost-effective alternative -plain
      old rock. Excavation is the simplest method of construction and the
      easiest for robots to perform and produces habitats which are naturally
      well shielded and need far fewer imported materials and components. To
      make excavated spaces habitable, one has a choice of using
      pre-fabricated pneumatic pressure hull modules near-term and
      application of plastic materials or surface sintering for sealing
      long-term. With hard rock materials no sealing may be necessary at all,
      simplifying things to the use of plastic sealed bulkhead units. (note,
      that when I refer to 'plastic' materials I'm not talking strictly of
      plastics like epoxy but rather materials that are plastic or semi-fluid
      in nature when applied, which includes cements and ceramics) Pneumatic
      hull aside, Savage's basic design concept quite practical for the
      excavated habitat -though limited in scale. The only difference is that
      the domed 'outside' area would actually be completely underground as
      well, relying on light brought in by optical fiber cable from arrays of
      external heliostats, and habitable space may actually climb the surface
      of the dome through inverted terracing to maximize space efficiency -a
      strategy once proposed for some arcology designs. Now, this might seem
      confining but bear in mind that the reduced gravity on the Moon and
      Mars allow for the construction of clear-span excavated spaces much
      larger in area than possible on Earth. So while domes as large as the
      vast crater domes Savage envisioned may not be practical by excavation,
      some very large chambers are quite feasible and can be developed
      incrementally. Lunar and planetary locations also offer some ready-made
      excavated structures in the form of caves and lava tunnels which
      greatly reduce the construction cost further and can offer spaces of
      truly vast area. It has been proposed that Martian lava tubes can be
      potentially ten times the size of terrestrial equivalents. Large cities
      could be contained in such spaces.

      The key limitation of excavated habitats is that locations suitable for
      safe excavated structures aren't always going to be in convenient
      proximity to key resources. Optimal locations with both suitable strata
      with a broad spectrum of nearby resources may be quickly depleted in a
      first generation of permanent settlement. To exploit other less optimal
      locations a subsequent wave of development would have to rely on built
      structures to locate settlement near them. These would be inherently
      more expensive but costs could be kept low using simple construction
      methods and architecture that mirrors the architecture of the excavated
      habitats, only with a built-up rigid shell structure made of indigenous
      materials. This basically comes down to the development and use of a
      material called 'regolete'. I use this term to refer to a broad class
      possible materials with one common set of characteristics; they are
      derived from regolith materials and take on the plastic and rigid
      characteristics of conventional concrete or geopolymers. It's difficult
      to get specific here because right now the chemistry of regolete
      materials remains a bit speculative. We know that a number of materials
      like this are theoretically possible but the specific forms they take
      and their phase-change characteristics still need to be researched. The
      environment on moons and other planets tends to be difficult for
      phase-change materials like concrete or polymers. They don't stay
      plastic for very long due to extremes of pressure or temperature or
      they don't change phase until very specific conditions occur. And, of
      course, it's going to be a bit different situation in each location
      about the solar system. We can, though, predict that regolete will take
      any of four forms with the choice of possible construction methods
      based on that.

      First is the in-situ stabilized regolith. This is the equivalent of
      cast earth; a mixture of earth in a fairly broad but inert mix of
      granular materials which is bound into a solid by a small quantity of
      phase-change material -typically clays as with natural cob or portland
      cement. Can be used much like conventional concrete in various
      slip-form, mound form, sacrificial form, or extrusion schemes. It is
      relatively weak and doesn't often bind well to reinforcement admixtures
      like polymer, glass, carbon, or alloy fibers due to the inconsistency
      in the material but is aided by large element reinforcement such as
      rebar or meshes. This generally means that much larger volumes of the
      material are needed to afford the same load-bearing performance and a
      point of diminishing returns on this limits maximum practical structure

      Next is in-vitro stabilized regolith. The analogy here is compressed
      earth block. Still a rough mix of materials bound by a small quantity
      of phase-change material but processed in a way that keeps the phase
      change process under more specific control and adds the benefits of
      special processing -like high pressure- to improve material
      performance. This would most likely be used in the space environment
      where the limitations of whatever plastic material is used as a binder
      cannot tolerate ambient environmental conditions, thus requiring the
      prefabrication of structures in a factory environment. Stronger than
      in-situ stabilized regolith would be and better able to use
      reinforcement admixture materials but still relatively weak and cannot
      be assembled without the addition of some kind of in-situ phase change
      material as a 'mortar' between components or the use of some kind of
      mechanical interface to lock pieces together -often both is employed
      with CEB. This has often been pointed to as a likely construction
      material for Mars based on experiments with Mars regolith analogy
      mixtures but construction techniques based on small blocks tend to have
      high intricacy and complexity which make them more challenging for
      robots to perform. So it seems much more likely a prospect used with
      very large prefabricated components that can employ mechanical
      interfacing to its optimum. For example, factory fabricated modular
      block and panel systems combing an alloy compression frame integrated
      into precision blocks and panels of fairly large scale. Or large
      prefabricated modular structures with formed-in-place pressure-tight
      interfaces. Again, clear spans will be limited because of weaker
      strength characteristics but much better than the in-situ stabilized

      In-situ formed regolete would be the optimal form of this material by
      virtue of maximum flexibility. This would be a highly refined material
      which behaves identically to concrete -even in the space environment-
      and can accommodate reinforcement fiber admixtures as well as larger
      scale reinforcement elements. In lowered gravity environments,
      structures as large as Savage's Avalon crater dome become possible with
      this material and a very broad range of construction methods can be
      employed that are relatively easy for robots to perform.

      In-vitro formed regolete. The conventional analogy here is materials
      such as YTONG autoclaved aerated concrete which must be processed in
      large autoclaves. Again, the chief benefit is refined materials
      offering better performance with this factory based approach in
      production used because the chemistry doesn't accommodate phase-change
      in the ambient environment. Unlike in-vitro stabilized regolith, this
      material is less likely to gain as much in structural performance as a
      consequence of this more controlled production environment because this
      is a more refined material to begin with. But the controlled factory
      production environment affords a large diversity of options in features
      that cannot be performed effectively in-situ. Would favor construction
      methods based on pre-cast modular components.

      A variety of construction techniques would be employed with these
      materials based on their type and the site situation. The most flexible
      would be those using the in-situ formed materials. Here the simplest
      technique would be mound-formed structures, a technique deriving from
      the technique developed for the construction of bunkers and
      bomb-resistant aircraft hangars built by German forces in WWII. Earth
      moving equipment would simply excavate around or mound up regolith in
      the forms of the structures needed and then a rigid shell would be
      formed by the mass loose pouring of a plastic material -a 'regolete' or
      regolith derived concrete- reinforced with alloy or carbon fiber. The
      finished shell would then be dug out, the loose material piled on top
      to provide further surface cover, and it could be sealed for
      pressurization using prefab pneumatic shells or application of an
      impermeable plastic material on the inside. This technique presents
      diminishing returns in efficiency the larger the structural scale
      because of the escalating volume of material that must be moved. At a
      certain scale slip-forming or extrusion based on robotic climbing form
      or boom positioned systems become more efficient despite their greater
      technical complexity and would tend to become the method of choice for
      this form of construction given sufficient regional industrial

      In-vitro formed materials are limited to prefabrication based on
      modular components. It is unlikely that the use of small scale block
      construction akin to contemporary adobe construction methods will prove
      a practical technique because of the physical complexity and intricacy
      of the assembly process. However, large precision block and panel
      systems using formed-in-place connector elements are a strong
      possibility. These would take the form of large blocks formed with
      interlocking shapes and which have mechanical connectors formed into
      them. One example might be a kind of compressed regolith block with a
      '+' shaped tubular reinforcement frame formed within it and made of
      alloy, ceramics, or pultruded fiber reinforced plastics. The frame
      element would have screw socket ports on the ends with two pre-loaded
      with hex screw pins. When a block is placed adjacent to another its
      interlocking shape connects it in place and then a key driver is
      inserted through the frame tubing to drive the pins to engage into the
      adjacent sockets, mechanically locking the block in place. This
      approach could be used with a variety of block and panel geometries and
      thus would allow for the construction of vaults and domes using panels
      in geodesic shapes. Large precast structures are also possible using
      habitat structural designs based on cellular geometries, much like that
      employed by famous Modernist designs such as the Habitat 67 project in
      Quebec. But, even with such materials, high wall thicknesses will be
      needed and so this limits this strategy to relatively small-span
      structures otherwise the modules become too large to be easily
      transported. Thus this strategy would tend not to be as efficient.
      However, there is the potential in this concept to construct large span
      enclosures from assembles of such modules, the individual modules
      serving as both individual habitat units while ultimately forming a
      shell enclosure around a large open-span area. Prefab structures would
      be especially efficient for the construction of enclosed walkways,
      roadways, railway lines as well as for tunnel construction in granular
      or otherwise unstable material strata. Simple corrugated arches -also
      likely made from rolled formed alloys- would be likely for this.

      Both in-situ and in-vitro materials offer options for light
      transmitting structures and this presents a key advantage of the
      built-up structure over the excavated structure. This is accomplished
      by the inclusion into the structure of fiber optic elements which
      transmit light from the outside. This is done using either small mass
      produced optical elements (combined conduit, mini-emmiter, and
      mini-collector in a single gradient index optic component) or aligned
      optical fibers formed in place during the construction or in-factory
      prefabrication process. An existing example of this kind of capability
      has been demonstrated in a prefabricated cement block product known as
      Litracon. (short for light transmitting concrete) There is some
      possibility of making such structures image transmitting as well as
      light transmitting with more sophisticated optical elements. This
      allows for the possibility of creating actual rad-sheilded windows of
      most any thickness. But this may be too expensive for large areas and
      so one would be limited to a translucent appearence, through with the
      potential for very high transmission efficiency. It would certainly be
      sufficient for the creation of a virtual sky appearance. However, light
      intensity may still need to be supplemented by either artificial light
      sources or the use of heliostats which effectively compensate for lower
      light levels by concentrating light from across much larger areas. This
      is especially critical to farming applications and the creation of

      Whatever construction approaches are used, we are likely to see the
      same basic architecture as employed in the excavated structures;
      'subtopolis' habitats based on the creation of relatively large clear
      span indoor spaces as household and community centers surrounded by
      smaller integrated spaces serving as generic spaces adapted into
      specific uses by retrofit. An inwardly-focused living environment that
      radiates around these 'indoor outside' spaces. Windows to the outside
      will be few and mostly video based. these may be quite comfortable
      spaces with all the attractions Savage envisioned for Avalon. But there
      will not likely be any grand views of the stars except by projector.
      The great transparent crater domes may become a possibility, but
      probably only with the advent of a robust nanotechnology able to
      replace regolete with an image-corrected light transmitting diamondoid
      material -which would develop as a direct evolution of the kinds of
      construction technologies I've here described.

      I consider Avalon to be a stage spanning all lunar and planetary
      colonization as the same basic strategy may apply throughout the solar
      system. I envision the long term support of these colonies being
      facilitated by what I refer to as 'cyclic shuttles'; essentially a
      hybrid of inter-planetary spacecraft and Asgard style orbital colony
      whose orbit is a perpetual transit orbit between key points in the
      solar system. These vessels continually travel, picking up and
      depositing people and goods between these destinations, being serviced
      by local shuttle vehicles and orbital stations at each location. Travel
      may not be fast with such vessels but it would be safe and very
      comfortable and with a regularly scheduled fleet of such vehicles large
      volumes of traffic can be supported.

      Eric Hunting


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