July 29, 2011

Could 100 Kilometer high towers usher in the next space age?


Patrick Vankeirsbilck
Question: How did the concept of the Spaceshaft originate?

Question: And this shaft is a single structure?
Yes, but to reach Space there would be a need of multiple shafts arranged inside one another and so combined into a telescopic system. The specs of each shaft would depend upon their intended operational purpose, functional requirements, the materials that will be used, etc. …. For example; shafts intended to operate within dense atmospheric regions have requirements that are different to those that will extend into thin density regions, and these have also different material requirements that the shafts that are intended to reach into space. Preliminary calculations which I have done indicate that with current materials we could reach heights of 100 kilometers. Ultimately we believe that structures as high as 300 kilometers are achievable.
Question: Would the shaft be made from Kevlar?
We are looking at kevlar or any other aramid-based fiber. We are examining composite materials made from Mylar. The SpaceShaft won't require any fundamentally new materials, such as carbon nanotubes. Composites currently used in aircraft can withstand extreme compression, so we are looking for partners who can provide the necessary computing resources and expertise to do the necessary testing. The computer modeling should give us the confidence to know that the materials can withstand the stresses.
Question: How would the SpaceShaft be constructed?
The basic concept involves using "lighter-than-air building blocks", which are partially inflated with Helium. The building blocks are basically converted science balloons that instead of having a payload gondola they have a skeleton with the equivalent mass. The skeleton is used to provide the geometry and mechanical functionality we ultimately need (as for the assembly process or to resist the compressive conditions the structure undergoes at altitudes where there is no longer buoyancy but pure weight). Prior to the fabrication and deployment processes we calculate the needed volume of the vessel as to keep the structure floating at a target altitude in which buoyancy is cancelled by the weight. The typical altitudes will range between 30 to 50 km.
Once the diameter of the sectional ring has been decided, we start building up, from the surface of our planet, letting each building section levitate enough (and under permanent control,) as to insert new building blocks right underneath. Once tightly secured to each other; both sets are made to repeat the described procedure. And so, with each new inserted module, even more buoyancy is achieved, pushing up the entire structure above and piercing through the weight barrier. The resulting artifact is not a tower, (because is not standing on a surface, or has foundations,) but it could be compared to a floating scaffolding structure. The beauty of this system is that we do not have to do any construction work at high altitudes; it will all be done at ground level-upwards, completely removing the imperative need of transporting building components using flying vehicles or rockets.
Once a stack of these sectional rings have an altitude that equals that of our original calculation for altitude, we know that the vessel at the top no longer has the desired buoyancy. But because there is an accumulation of buoyancy from underneath, the vessel will be jacked-up to a higher level and so this effect is repeated for a known number of times, up to a chosen targeted altitude, such that of the Karman line which is the official borderline that delimits the aerodynamic atmosphere from space.
Question: Wouldn't helium be too costly to float this structure?
Using Helium exclusively is clearly not feasible; besides its cost, we would need to consume up to 35% of the world's annual Helium extraction just to deploy a one time SpaceShaft. Hydrogen gas is not an option, due to flammability issues. And there is even another problem; some gas will leak out, although we don't expect this to be a major problem if neglected. To resolve these issues we are developing a mechanism by which the need of Helium can be reduced by up to 50% of the total need and keeps the gas from escaping out to the atmosphere due to desorption through permeation, (a process in which the small molecular size of the He. atom finds a way out of the pressure vessel through the porosity of the containing membrane).
Question: How well will the system handle the failure of an individual module?
The system will be designed to tolerate the failure of individual and multiple modules.
Moreover, the SpaceShaft has the added benefit of being mainly buoyant at low altitudes, (this is due to the inherent buoyancy of the HyperCubes,) and so making it more unlikely to collapse. Which is a behavior opposite to that of a compression structure, (that would first bend followed by collapse,) when a significant number of modular failures are achieved. Furthermore, we also envision the implementation of secondary systems to perform the necessary maintenance on damaged modules, so that the entire system should be quite safe to operate.
Question: How would you send people up the shaft?
Although there are windowed elevators on the outside of a SpaceShaft, (that could provide for some form of entertainment, certainly the view alone would be breathtaking,) these are mainly meant for localized maintenance and would only climb through atmospheric altitudes located between sea-level and mid height elevations. Actual transport to the edge of space will happen by the service of a shuttle travelling within the conduit of the central shaft. For sure both sets of elevators, external and internal, would allow tourists to stop at the amenities on platforms built on the mooring hubs.
Question: What diameter would the SpaceShaft need to be?
The larger the diameter of the shaft, the stiffer it will be, and the less effort that will be needed to keep it stable against side winds. To get a better sense of the dimensions we are talking about, at sea level; the diameter of the shaft will be about one kilometer, while at the top about 100 m, pretty much like a gigantic tapered mast. It is important to underline that the system is tapered because is telescopic in nature, (that the external tubular shafts allow for the innermost ones to move vertically,) and that guy lines are also used to force it to a vertical orientation.
Question: Couldn't you use the elevator as a pulley, to bring cargo to the top with minimum energy?
Yes, but this configuration is so inefficient that it is a completely undesirable mechanism. Whereas our system is designed to be a much more efficient elevator system, in which a pair of active mechanisms are simultaneously employed. The main mechanism, being that of the deployment process itself, whereby payload is placed inside containing spaces of selected HyperCubes that make up the sectional rings and are elevated together with the whole structure while this is being jacked-up. Such a method follows a "first-in to first-out" logic sequence (FI-FO). Although this is a relatively slow uni-directional mechanism, it has extremely powerful lifting capacity, is inexpensive, clean and is reusable. This method would allow for a CONSTANT FLOW of sectional rings, (with their contained cargo,) to be dispatched at the top. By doing so, we should be able to transport, in a continuous flow, thousands of tons of cargo, (or rockets,) just by using this method. The other system consists of a fast, bi-directionally travelling, hybridly powered shuttle. However, with a significantly lesser carrying capacity, but still comparable to current rocket systems and would also allow for passengers transport.
Question: How difficult will it be to fabricate these rings?
We have been in discussion with companies and some Universities here in Belgium as to how to construct these rings. This concept doesn't appear to be present any intractable engineering problems; the biggest obstacle at this point is a lack of funds.
Question: Assuming sufficient funding, how long would it take to construct the first SpaceShaft?
Once the infrastructures to fabricate the building blocks and that for the deployment of the rings are in place, I estimate that we could construct a 100 kilometer shaft within a year. Every hour or so, a ring could be placed underneath the stack. We could have the necessary infrastructure within five years. Material costs for a 100 km shaft would be about 40 million Euros, so the entire 100 km structure would cost perhaps 40 million Euros to build. That doesn't include, however, the costs of building the factory to fabricate the building blocks. Such a factory could easily cost 60 million Euros or more. So a very rough estimate is that we could create a 100 km SpaceShaft for 100 million Euros.
Question: What is your assessment of the space elevator?
We have studied the concept of the space elevator, and we hope that the idea eventually comes to fruition. But there are a number of daunting and unresolved technical challenges to creating such a space elevator. First, for the tether, one has to fabricate huge quantities of carbon nanotube filaments. Then, as to provide the counterbalance to stretch the tether, one has to have a substantial counterweight at the top end-point of the system at a far away distance nearing 140000 km. Then avoiding collisions with satellites would be problematic. By contrast, the SpaceShaft paradigm is doable, now, with current technology and compatible with "NASA's Proposal for a Balloon Assisted Launch System” [[1]].
Question: What would the primary benefit of a 100 km SpaceShaft be?
The primary benefit would be to have a permanent and inexpensive means of getting payloads, (and space vehicles,) up-to and from the edge of space. At 100 km, getting into orbit is much easier than from the ground. Space vehicles, such as SpaceShipTwo or Pegasus XL, could then takeoff from the fly deck on a tangential direction, (relative to orbital paths,) and so benefitting from the gained free-ride velocity attained during the ascent. So the cost of getting payloads into orbit using a SpaceShaft would perhaps be about 1% of the cost of using conventional rockets.
Tourism is another market; since each SpaceShaft could easily accommodate hundreds of tons of cargo on their fly-decks, and a craft operating above the atmosphere wouldn't need landing gear, wings, or aerodynamic surfaces. Space vehicles such as those previously mentioned could then takeoff and travel from one SpaceShaft to the other in just a couple of hours. And so we could provide intercontinental transportation without polluting the atmosphere.
And we are even looking into the possibility of using high altitude structures to change the planet's climate.
Question: How would the risk of collisions with planes and satellites be addressed?
Obviously this structure would need to have warning lights, but also have a surrounding no-fly zone, to keep away unauthorized visitors. Furthermore, an Air Traffic Control service will be necessary.
Because your question involves two different flying environments, it also deserves two answers; one regarding a dense region of the atmosphere and one for a region that is of very thin density.
At dense atmospheric regions!
Since most parts of the system are buoyant, the structure could survive a collision with a large object and falling debris are of concern at ground level. If severed the top structure would go down slowly and special procedures will be followed as to re-unite the sections. If there are multiple severed sections; these would eventually become floating objects, laying on a resting horizontal position, at altitudes anywhere between 25 and 50 km, from where they could then be salvaged.
At thinly dense atmospheric regions!
Two severed section: Lower section remains standing. Upper section, (found at heights outside the dense region of the atmosphere,) should quickly fall down, loosing momentum and speed; this would eventually become a floating object, finally laying on a resting horizontal position, (this final condition would happen at altitudes anywhere between 25 and 50 km,) from where the section could then be salvaged.
Question: Could a 100 kilometer SpaceShaft be fully operational within a decade?
Assuming sufficient funding; we could even have a pair, or more, of operational SpaceShafts within ten years. Even just having a pair of these could allow us to have combined operations between both SpaceShafts; like having a ferry transportation service occurring at LEO from one fly-deck to the next.
It is important to recognize that since the beginning of written history we have evidence of how skilled humans are in building increasingly sophisticated and taller structures. Mostly these improvements have had major steps forward thanks to the discovery on how to use the existing materials at hand and with the very particular properties needed and the development of the necessary newer techniques for their employment, and as a result achieving incredibly new heights. So it is pretty much a matter of accepting the engineering challenge in learning how to use the materials and developing the construction skills.

[1] www page; “Proposal for a Balloon Assisted Launch System” at http://space-academy.grc.nasa.gov/y2008/group-project/proposal-for-a-balloon-assisted-launch-system/


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