First proposed by Russian scientists early in the 20th century and toyed with as a thought model by countless engineers around the world thereafter, the concept of a built tower to orbit saw its first description in modern terms in the 1970s by science fiction writer and inventor of the concept of the geosynchronous satellite Arthur C. Clarke, in his short novel The Fountains of Paradise. Inspiring the imaginations of many to follow, the concept was long regarded as impossible due to the limitations of any known materials. But, much as Clarke himself had predicted, the potential solution emerged in the realization of nanofabricated materials and the development of carbon nanofiber. Now regarded as a potentially imminent reality, at least two commercial companies now actively pursue the development of what is commonly referred to as a ‘space elevator’ system and X Prize Cup events conducted yearly in New Mexico have featured competitions for the design of a practical robotic ribbon climber that can support transport to space.
For TMP2 the space elevator concept represents the ideal form of transportation in the context of Bifrost –the most efficient way to employ renewable energy collected by OTEC in the form of electricity for bulk transit to space. But in TMP2 we envision the space elevator across a much broader plan of development than any currently envisioned by this technology’s current commercial developers. Aquarian marine colonies would play a crucial role in the development, operation, and expansion of the space elevator system. Historically, cities tend to emerge at strategic points of intermodal transit exchange and the space elevator would be no exception to this. Thus we envision the terminus points of a space elevator system –the marine ‘Downstation’ and GEO ‘Upstation’– being logical locations for settlement development. In the Aquarius section we’ve discussed the marine colony Downstation role in the section Aquarian SE Downstation. We will also be discussing the upstation role of Asgard phase settlements in the sections on the Modular Unmanned Orbital Laboratory - MUOL and Asgard SE Upstation. In this section we will explore the creation of an early space elevator system and how we expect it to evolve on its way to a robust high volume transit system hosted by what may become the largest of marine and Earth-orbital settlements in future human history.
Bifrost Ribbon: The first-generation of space elevator system is likely to be based on the deployment of a single thin pre-fabricated nanofiber ribbon from a deployment and counterweight platform launched to GEO by –most likely–use of a larger scale Exocet vehicle with several launches lofting the components for on-orbit assembly of the platform. Essentially, the deployment platform would be a kind of MUOL which may be assembled at LEO and self-propelled whole to GEO or may be assembled at GEO, depending on the kind of launch capability available at the time. It would be hosted by and deployed between a pre-constructed GEO MUOL Upstation facility and an Equatorial positioned Downstation PSP platform which may, or may not, already be associated with an existing Aquarian marine colony or which may evolve from an Equatorial Marine Space Center facility supporting the launch of the deployment platform.
For an orbital structure to remain in GEO, its center of gravity must be located at the GEO point. Thus a tether system extending from GEO to sea level must have an equivalent amount of mass equal to that long structure located opposite it from the GEO point. Early systems of this type based on a single thin ribbon of relatively low mass will likely employ their own ribbon deployment structures, transport spools, as well as portions of their GEO booster vehicles as a counter-weight mass. Later on, this will not be sufficient and so as the structure is expanded it will likely evolve into a continuous tether structure twice the span to GEO, extending as far into space as it extends to the sea, this outer-orbit structure being used as a means of inter-orbital launch for modest vehicles carried along it to select release points by exploiting centrifugal force.
Deployment of the initial ribbon would require the on-orbit assembly of a deployment platform structure combining a MUOL-like platform, a ribbon spool with ribbon tractor to deploy it, a ribbon braking and clamping system that will eventually attach the platform to the deployed tether, attitude control systems, a booster thruster system, power systems, a transceiver for tele-operation, and a telemetry system tracking, in concert with Earth surface telemetry, a small transponder pod on the ribbon end. This transponder pod would feature its own attitude control and aerodynamic surfaces intended to control twisting of the ribbon as it descends. The descending ribbon would not be subject to an reentry friction because it has no velocity relative to the Earth surface but would be subject to winds in the atmosphere and loads, vibrations, and twisting moments on its length. As the ribbon is deployed, the deployment platform must, using its own propulsion, slowly climb in altitude to compensate for the mass descending to Earth. This would likely be performed using some form of continuously operating plasma thruster powered by stored energy, solar power, electrodynamic tether, or projected energy from the surface. Upon approach to sea level, the ribbon would be intercepted by a pair of tow ships pulling a capture line between them that snags the transponder pod as it hits the water. The ribbon would then be transferred to the nearest of these two ships by which it would be towed to its anchor structure within the initial Downstation.
The initial Upstation would be a fairly simple affair and may be built some time after the initial SE ribbon is deployed. MUOL structures employ a modular planar truss as a backplane for the attachment of modular support and service systems –power and radiator panels, communications transceivers, attitude thrusters, control systems, and robots– as well as providing leased space for self-contained tele-operated laboratory and factory modules. To link to the SE tether, this structure may employ a ‘terminal’ or ‘port’ in the form of a radial space or hole in its planar truss through which the tether passes or an adjacent section of the plane truss with perpendicularly arranged service booms. Initially, the Upstation may be physically disconnected from the tether, allowing it to stand free of the MUOL structure whose attitude control systems would be intended to keep it just within the reach of its on-board service robots for access to its simple ribbon climber vehicles and cargo transfer. Alternatively, the Upstation structure may lightly attach to the ribbon by low-tension clamps designed to allow the tether to move independently of the station structure in the event its own movement causes tension that exceeds a threshold that might potentially break the ribbon.
The initial Downstation facility would be similarly simple, consisting of a ribbon anchor in the form of a spool and a ‘service well’ topped by a movable roof and contained in a building atop a PSP platform using active stationkeeping. This building would feature a radial series of service bays around the well space in which ribbon climber vehicles are serviced and payloads for them prepared and installed. The top or perimeter areas of the Downstation facility would host a series of power projectors using targeting masers or lasers to supply power to the ribbon climbers. Solar arrays or a modest scale OTEC plant would provide power for these systems. If evolved from an existing Equatorial Marine Space Center, the Downstation may feature many supporting structures and worker accommodations as well as helipads, a full-service container terminal, possibly an airstrip, and facilities associated with the launch and flight management of other spacecraft. The Downstation may also be an add-on to an existing marine colony, which would offer all these features and more while being more specialized in function and structure itself.
The initial climber systems would be simple robots that use a kind of caterpillar band or multiple tractor rollers to engage the ribbon with minimum slippage that would produce potentially wearing abrasion. Roller elements are likely to be self-contained motors, as is common with some forms of conveyor belts. These would be driven by an electric power system featuring a set of supercapacitors for power storage. A light space frame structure would host the active components and provide attachment points for payload as well as a wide but feather-light array of photovoltaic film or laminate microwave rectennas. This array is used to collect power broadcast from the Downstation and, eventually, from both Downstation and Upstation.
The initial space elevator system would be a very minimalist affair, supporting perhaps no more than a few hundred kilograms in payload capacity on robotic climber vehicles that may take a month to reach orbit. While this precludes any human passenger travel for a very long time, this well suits the use of MUOL facilities that need only modest payload support and are entirely tele-operated, the Downstation providing the shortest-path/lowest-latency communications link for such a facility and thus a logical location of its operations center. But the ultimate goal of SE development is the realization of a bulk transit system with passenger capability. This will require a continuous program of evolution and expansion for the system.
Multi-Ribbon: The straightforward form of expansion –and for that matter repair– for the SE is simple lamination of additional ribbons to make a progressively thicker structure that can support a progressively greater payload fraction. This process would be performed by climber vehicles whose payload is a spool of added ribbon and an additional lamination system. The problem with this, however, is that this expansion work could be very protracted, with a single lamination run taking many months during which the systems is unusable for transportation. As MUOL facilities on orbit expand, their support will demand increasingly routine transit. While this could be temporarily supported by conventional spacecraft, a more efficient approach would be to simply multiply the system using several adjacent ribbon tethers which can be operated, maintained, and expanded independently of each other without disrupting routine transit. This form of expansion would be anticipated in the design of the initial deployment platform units, which would be designed for on-orbit docking. This way additional ribbons would be deployed at some distance then slowly brought together so that their deployment platforms can dock, putting them at a distance within several meters of each other at the up and down stations.
By using multiple tethers it not only becomes easier to expand the system by increasing the thickness of ribbons individually, it also becomes easier to obsolesce the original deployment platforms as counterweights, convert them into a unified structure, and extend the length of the ribbons farther into space. By linking together, the multiple deployment platforms become a unified mass allowing their individual components and structures to be disassembled by incremental transfer to other portions of the overall structure. Individual ribbons can be released from their original deployment spools and attached to new ribbon extensions that will incrementally replace the original deployment platform mass. After several ribbons are thus integrated and their original hardware discarded, the collective counterweight structure would be reduced to a much lighter space frame release station and ribbon spacer, allowing additional ribbons to be added by adjacent tether deployment along other tether ribbons starting from the GEO Upstation position. A number of similar release station structures may ultimately be added to the now freely extended ribbon array, both above and below the GEO point.
Bifrost Tether: The ultimate objective of expansion of the SE tether structure is to realize high-speed transit. This may only be possible by a replacement of the primitive climber robots with a linear motor system that would allow vehicles to be propelled along the tether at high speed while being physically separated from its structure by magnetic fields. This would require the tether to incorporate elements of this linear motor drive and to be able to supply power to this system more directly, rather than relying on energy projected from a distance. All this must be done at a very small fraction of the load capacity of the tether. Thus it’s anticipated that the expansion of the multi-ribbon array would eventually lead to their unification into a large corrugated structure with a radiating array of internal channels.
This evolution of the structure would thus produce a unified tether that can support multiple simultaneous activities and perpetual maintenance and expansion. As maintenance and expansion work are performed on the exterior of the structure using slow-moving friction vehicles, interior channels would be used for primary transit using independently running high-speed linear motor elevators. These elevators, composed of open space frame structures integrating their radial drive elements, would be able to reduce transit times to GEO to perhaps a single week and would be scalable with the load capacity of the overall tether structure in the manner of a railway train.
This new elevator system would require power supplied internally all along the tether length. Using a space elevator as a power conduit has sometimes been a controversial subject owing to misunderstood claims for the potential superconductivity of carbon nanotubes. It’s unlikely the physical structure of the tether could be practically used as a conductor –at least not over it’s vast length. And adding superconductive materials to the structure would have a high load cost. But a simple and practical solution may be to use channels of the tether as evacuated waveguides for laser or microwave energy injected at both ends of the tether and tapped to power portions of the linear motor tracks by photovoltaic or rectenna arrays placed at intervals along the channel length.
As the tether expands in diameter, its most central channels would become increasingly well shielded from Van Allen Belt radiation. Eventually this would allow for largely unshielded elevators based on TransHab-style pressure hull systems to be used for routine passenger transportation. (infrequent passenger transit may come earlier, but would require heavily shielded elevator vehicles that use so much mass in shielding they may be limited to no more than one or two passengers) These passenger elevators would, unfortunately, be windowless save for possible virtual window displays but would otherwise be comfortable, feature extensive personal communications and media entertainment, carry their own food and water supplies, and would be equipped as small spacecraft with their own life support systems. Following the long-distance transit service model of the Circum-Equatorial Transit Network they might even employ an on-demand transit service model based on a personal elevator capsule design featuring the accouterments of a fine hotel suite, depending on limitations of payload mass efficiency.
As the tether comes to support much more elaborate transportation, its up and down stations would likewise need to become larger and more sophisticated. The use of a corrugated structure requires a more complex terminal structure to allow access to the individual channels. At the Downstation, this would take the form of a large multi-level terminal structure inside which the tether is literally peeled open to fan out like the roots of a tree to open its channels for access from underneath, the outer-channels on upper levels, inner channels on lower levels. A more detailed description of such a facility is featured in the article on the Aquarian SE Downstation. Similarly, the GEO upstation facility would see its portion of the tether stretched apart into a basket-like structure spanned by compression frames allowing the channels to be accessed from the side. This complex structure may eventually for the basis of a ‘core truss’ for a very large EvoHab space settlement and also a junction for a new tether structure extending perpendicularly along the path of GEO.
With such a corrugated structure the tether would, like the stalks of a plant or the trunk of a tree, be able to freely evolve through a combination of incremental expansion and demolition. As new material is added to the exterior, other portions of the tether may be stripped-down to open up larger channels or alter their profile. This would allow every portion of the structure to be incrementally repairable and upgradeable forever while never needing to halt its transit use. As new materials develop, they could be incrementally incorporated into the structure to improve its performance. The three most-likely radical improvements implemented in this way would be the replacement of early nanofiber materials with monolithic diamondoid applied in prefabricated laminates, in-situ application of monolithic diamondoid by NanoChip or Free Moving Assembler systems, and eventually the subsuming of the tether by NanoFoam matrix.
Eventually the Bifrost Tether may evolve –well into Asgard and beyond– to a structure comprising dozens of channels each up to 6 meters or more across and hosting elevator vehicles up to 15 meters long –possibly in ‘trains’. The upper terminus of the tether may host a large station in partial gravity built right inside some of its channels and using the end of the tether as a launch tube for elevator cars adapted into complete spacecraft. With other such launch tubes branching off of outer channels, the SE may become not just a means to access GEO but a gateway to the near-Earth system and other settlements in it. The Downstation may become the largest of all individual Aquarian marine settlements, linking the SE to the world through its connection to the Circum-Equatorial Transit Network. Meanwhile, the GEO Upstation may become a node on a second orbital tether that may one day run completely around the Earth with multiple SE tethers linking it like spokes on a wheel. Serving as the core structure of innumerable settlements and facilities, it may become Earth’s largest single inhabited structure.
But perhaps long before this, the Bifrost Space Elevator, in even its earliest forms, may achieve a psychological connection to space for human culture like no spacecraft has ever managed. No longer will space be merely an ‘un-place’, an abstraction. It will become a realm physically, tangibly, connected to the Earth, the space elevator an umbilical cord for a nascent extension of civilization emerging there.
- Mountain Waverider
- UltraLight SSTO
- Marine Mass Launcher - MML
- Bifrost Support Systems