If you don’t fund my particular hobby right now, life has no meaning for anyone, anywhere!
You wish !
I would suspect that your life has very little meaning ,now ,I know you .
Don’t insult other posters in this forum.
Stranger On A Train, I’m enjoying your posts in this thread a great deal, and wanted to say thanks – just in case you feel you’re shouting into the wind. I’d certainly feel that way.
I’m quite curious about your “ellipsoidal shell constructed of long-fiber reinforced silicate-water ice matrix” habitat, but I’m not sure I have even the vocabulary to ask interesting questions. I’ll try anyway, please bear with me:
- What does “long-fiber reinforced silicate-water ice matrix” mean? Plastic embedded in frozen water?
- Obviously the water is a shield against radiation, correct?
- Is it frozen at the interior surface, where the “islands” lie, or only the exterior?
- If it’s frozen at all, we’re obviously spinning the habitat, or in shade or… something…?
- When damaged by “a 10m bolide (by self-scabing of ice)” would it need exterior repair, or does the ‘scabing’ (not sure what that means - “scabbing” ?) accomplish that?
- How do you see going from “a nitrogen filled balloon a few kilometers” to that habitat?
- I assume ellipsoidal means generally “egg shaped” I’m guessing a spin would be applied around the long axis of that egg for gravity, yes?
- What approximate size is this habitat for 10k people? 50k?
If any of the answers to these question are onerous, please give me some notions for asking more targeted questions. I can see you like writing precisely, and I really appreciate the detail you’ve been willing to go into in this thread. Thanks!
I’m going to take a stab at this, mostly for the practice. I’m sure Stranger will be along to correct me.
*- What does “long-fiber reinforced silicate-water ice matrix” mean? Plastic embedded in frozen water? *
Not plastic - silicate. I think he’s thinking of quartz fibers, though he might mean clay or rock. Think asbestos.
- Obviously the water is a shield against radiation, correct?
Well, it’ll do that too, but mainly it’s there to walk on and hold air in - it’s the main structural component.
- Is it frozen at the interior surface, where the “islands” lie, or only the exterior?
No, he means literal (artificial) islands, on literal liquid water.
- If it’s frozen at all, we’re obviously spinning the habitat, or in shade or… something…?
Definitely spinning (for “gravity”).
- When damaged by “a 10m bolide (by self-scabing of ice)” would it need exterior repair, or does the ‘scabing’ (not sure what that means - “scabbing” ?) accomplish that?
Yes, “scabbing” refers to ice flowing to fill holes.
- How do you see going from “a nitrogen filled balloon a few kilometers” to that habitat?
In layers, I assume.
- I assume ellipsoidal means generally “egg shaped” I’m guessing a spin would be applied around the long axis of that egg for gravity, yes?
More or less, and maybe, respectively. The stable spin for an ellipsoid is around its minor axis, so I at first thought he might be imagining an oblate spheroid, a=b>c, but close to a=b=c. However, this is a horrific waste of volume, so he’s probably thinking “screw it, we’ll use active stabilization,” in which case it would be long and thin, and spinning on the major axis.
- What approximate size is this habitat for 10k people? 50k?
This depends on the design selected above. A 100-meter-deep ocean would utilize a large fraction of the available surface area of an ellipsoid 1 km in diameter, so you could support 10,000 people in such a structure as little as 4-5 km long. Disaster-proofing and less reliance on external supplies and/or hydroponics would require considerable revision upward (factor of 100, perhaps?), but Stranger is more qualified that I (in many respects) to speculate further. To support 50,000 people you’d … just make it 5x longer? That doesn’t seem right, but I’m getting tired.
Thanks for taking a stab at that, Nametag.
Ah, ok, thanks. But it’s embedded in an “ice matrix”. I’m unclear how the ice got frozen or stays that way, unless there’s an great big sun shade over the structure. I guess I’ll wait for Stranger to check in, if he feels like adding something here.
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Which again implies the water (or at least a lot of the outermost water) is frozen (however it got that way), else the egg would just change shape if you spin the long axis – that axis would turn into the short axis when the shape flattened and all the water sought the “sides” of the egg because of the spin. Hmm.
I also forgot to ask Stranger what he meant by “stabilized by a keel system”. Some sort of light pressure sail to orient the spin axis?
Colonizing other planets is the future of the human race if not sooner than definitely later, but we probably won’t get to that point because so many people still don’t believe in Global warning or the fact it could wipe us all out in the next 40 or so years.
As for space colonization, eventually it will be necessary for more resources, if not for earth, as simple ways for providing for excess populace. As for logistics, Nuclear power, Solar power, water can all be recycled (food can be grown in almost greenhouses, I imagine something along the lines of what you see in the movie Sunshine)
Self sustaining colonies are not hard but we can’t even do that on earth soooo
Edit: The asteroid belt is very rich in minerals and private industry will jump on that as soon as technology makes it possible
Nametag answered all of the questions more-or-less correctly, so rather than just repeat his answers I’ll elaborate a bit on what features should be considered in constucting a habitat, how this structure is constructed and why I think it is a better type of habitat structure to start construction than O’Neill cylinders, Bernal spheres, Stanford toruses, and so forth.
One of the things that are lacking in most concepts for habitats is how easily they can be assembled and where the materials will come from. Most assume a metal and large (presumably glass) windows as the substrate, but the energy required to manufacture finished construction materials and the effort required to assemble even modest sized structures is enormous, as we’ve learned from the ISS. A viable habitat really needs to be constructed from minimally processed available raw materials (water ice, silicates) and able to be assembled starting from a relatively small structure that can be grown outward rather than assembled from individual pieces. It also needs to have sufficient mass to block radiation, be robust against micrometeorite (and hopefully larger) impacts, and be thermodynamically self-regulating or at least have enough thermal inertia that runaway heating or cooling can be observed and fixed.
The basic method of construction is to start with a large “balloon” of fiber-reinforced fabric a few hundred meters in diameter. (I’ve assumed fibers–both long and short–are s-glass fibers as they should be simple to manufacture, but other types of silicate and carbon fibers could be used) which is inflated using nitrogen at around 2 kPa. (Nitrogen is used because it is relatively inert, but any other non-oxidizing gas such as argon could be used as well. Since we are pressurizing at low pressure, the porosity of the fabric doesn’t matter too much since flow rates are low.) Once inflated, it is started rotating slowly about the axis as a slurry of water ice and silicates is sprayed evenly on the surface. Once a relatively rigid shell is formed, it is overwrapped with long fibers laid in a helical pattern, similar to the way composite overwrapped pressure vessels are formed. Once the structure has sufficient thickness and hoop strength, the rate of rotation can be increased to an equivalent radial surface acceleration of ~1 m/s[SUP]2[/SUP] and cuts selectively made in the outer shell and reinforcing fiber while material is added to the inside. The resulting hoop tension will cause the shell to grow in diameter, and additional fiber is overwrapped in a flaked pattern to control the expansion, as well as being covered with an outer reflective quilt to limit sublimation due to solar radiation.
Once grown to the desired size (depending on size this may take between a few weeks to several months) additional reinforcement is applied and the structure can be spun up to the desired final rotation rate (presumably providing ~10 m/s[SUP]2[/SUP] of radial acceleration). Pressure is increased and oxygen may be added to form a breathable atmosphere while a fiber optic light tube attached to a large array of parabolic light collectors is inserted in the middle to provide illumination and heat. (The outer surface of the light tube can be selectively mirrored or covered to control incident light and provide light cycles.) Now liquid water can be added to form an interior sea over the inner surface (along with more silicates and rocks to form a seabed which will both insulate and provide a place for coral and plants to grow), and floating “islands” (bedded with a lightweight pumice on top of icebergs) developed and anchored to the seabed. Once you have that, you then have to develop the islands as arable land, transportation systems, et cetera, all of which I leave as an exercise for future work.
The advantages of this over other manufactured structures with a relatively thin metal substrate are manyfold: in addition to blocking radiation, the mass of the water and silicate shell also forms a protective layer that can block small meteorites, and if punctured, the lower layer of the seabed, forced out by hydraulic pressure of the ocean, will fill and patch the hole (later to be reinforced, but does not require complete repair the way a punctured or buckled metallic structure would). The sea itself provides not only an enormous water reservoir (blocking even more radiation, to the point that background radiation levels would probably be significantly lower than Earth’s surface) but also will contain a substantial amount of dissolved oxygen and can be used to mediate oxygen and carbon dioxide concentrations in the atmosphere. It also makes for a great thermal mass which readily receives heat from its surface and returns it to the atmosphere via evaporation, which would allow the structure to remain at habitable temperatures for weeks or months even if the solar collector is lost or damaged. This also provides clean water without processing and maintains a hydrologic cycle suitable for growing crops. In an emergency such as a large incoming bolide, a few kPa of interior pressure can be vented through ducted nozzles to allow the structure some degree of propulsion independent of any external systems.
There are limits to the size this structure can get before the tensile loads become large enough that the fiber reinforcement cannot prevent the ice from continually flowing, but it should be feasible to get a structure at least 4 km in diameter and up to 12 km long, giving a usable surface area of somewhere around 125 square kilometers. Assuming that the islands provide habitable space of 1/4 of that, you have space for around 10,000 people at densities comparable to developed urban centers, while still having plenty of space for agriculture and aquaculture. (The structure can potentially be larger if you can stabilize the ice flow, but it is probably wise to limit the length to diameter ratio to prevent low frequency torsional and bending modes which make become destructive–another problem not addressed with Stanford toruses and the like.) It would certainly be possible to string a number of these together like beads, all feeding from a single large solar array, and with a “keel” made of a large bulk mass (extra material or processing waste) at the end of a long tether which maintains tension and keeps the array and habitats aligned by tidal forces. (This also allows for a quick means of changing the orbital parameters to avoid an incoming threat; cut the tether, and the released energy causes the habitat to fall sunward while the keel goes outward.)
Note that while this would not be cheap to do, it doesn’t require any exotic materials or large space manufacturing infrastructure; it mostly requires the ability to move moderate sized masses, provide logistics for the necessary manufactured materials to space (e.g. the solar array, fiber), and manage large scale projects. Most of the actual work can and would be automated as it is handling bulk materials rather than assembling discrete components. Any estimate of cost is necessarily speculative, but a first order evaluation of the necessary technology and effort comes in at less than US$500B, making it cheaper than a realistic crewed planetary mission and providing a resulting system which may then be used to support other space developments as well as a genuinely self-contained, sustainable habitat. The timeline on which this could be feasibly accomplished is 30-50 years (possibly faster with advances in propulsion technology, which is really the biggest limiting factor and technology hurdle), and can be developed and validated by proof-of-concept efforts on a significantly more modest scale; that is, we could use the same methods to construct a 100 m diameter structure in libration or Lunar orbit using materials from a small near Earth asteroid.
Such a structure would not only provide habitation, but probably makes more sense as a spacecraft for crewed extended duration exploration, especially in high radiation environments such as Jupiter (although that would require either a gigantic solar collector or some artificial power source) and provide the basis for outposts around the Solar system without the hazard and effort of landing and lifting people and materials from planetary bodies.
Stranger
Wow, Stranger that’s awesome, and much appreciated. I’m going to have to reread that a few times before I can ask (semi)intelligent questions.
ETA: OK, one question off the top of my head: what keeps the ice frozen? If sunlight warms the structure, the heat has nowhere to go doesn’t it? I’m thinking of your discussion of this problem in the generation-ship thread, and it was characterized as a real problem. Why is it different here, or is it? Wouldn’t the structure slowly warm up, all the ice melts, and the structure is no longer rigid, which sounds really problematic.
An excellent plan for a rotating habitat made with available materials, Stranger On A Train.
One possible improvement might be to reduce the rotation rate to the minimum safe level; it may not be necssary to maintain one Earth gravity inside these strucures, and any reduction in rotation rate would enable the structure to be correspondingly larger.
Humans would almost certainly be perfectly healthy at 0.9 gravities - the optimum level might be as low as 0.7 or 0.5 gees, or even lower. Earth has the highest gravity of any object that a human can actually stand on in the Solar System; if we are serious about colonising, humans will need to adapt to lower gravity regimes.
As a longer-term project, one might like to consider the colonisation of the most Earth-like environment in the Solar System; the 50km altitude level in Venus’s atmosphere.
Here’s a paper by Geoff Landis that decribes how to do it, (but not how to fund it)
Basically you build floating habitats supported by breathable air (or by nitogen balloons and a smaller amount of breathable air). Air and nitrogen balloons float in the CO2 atmosphere of Venus of course, and the temperature and pressure at 50km is comparable to that on Earth.
Problems include the superrotating atmosphere, and the dearth of water in this location.
There are other ways to exploit Venus, as well; solar powered skimmers could extract CO2 from the top of the atmosphere, exporting usable carbon and oxygen (plus nitrogen, a useful resource in itself).
Stranger,
Are there any tasks at which astronauts would be significantly better than robots?
What would it require for a ship to be able to supply food, water and oxygen to a small crew for several years?
Normally I’d send a link via PM but as this isn’t possible, I was wondering if you’d like the game Kerbal Space Program. If you’d give it a try, I’m sure many people would love to see your designs:
The outside of the structure would be covered with reflective foil, and because the system faces the solar collector toward the Sun the structure is generally in permanent shadow. Unlike an interstellar craft, the power source is external (i.e. the Sun) which can be moderated to provide only the necessary heating and there is no propulsion system generating waste heat. As much of the structural mass is at or below the freezing temperature of ice there is considerable latent internal (negative) energy to keep the shell frozen in addition, and most of the active energy in the system is “stored” in dynamic processes (the hydrological cycle, plant life, et cetera) preventing it from being released as heat quickly as it would be with a nuclear reactor or heat engine.
I wouldn’t assume this is a true closed cycle, either; obviously, additional materials such as metals would be mined from asteroids and delivered for processing and manufacturing, so additional compounds (water, nitrogen, hydrocarbons) could be used to cool the structure via evaporation if the radiative surface is insufficient to maintain thermodynamic equilibrium. I’ve run some basic 1D heat transfer models which indicate that it it should be easy to maintain equilibrium conditions that keep the seabed near 0 °C. I’d like to run more detailed simulations which include a basic internal climate and ocean model, but I’m still trying to develop the necessary skills to construct a 3D radiation and convection model (and using this as an excuse to learn an open source CFD/PDE solver and libraries as well as learning more about climate modeling).
As we have essentially no data on the long term effects of a lower gravitational field on people or animals I’ve assumed a 1 G field is desirable, but yes, reducing the required gravity reduces the spin rate and the hoop tension, allowing larger habitats at the same material strength. Part of the development and proof-of-concept process would be determining the level of simulated gravity required.
The pressures and temperatures are roughly Earth-like, but other conditions are not. Although the concept is certainly plausible, it would require significantly more technology, specifically resisting the highly corrosive atmosphere, power (even at 50 km the amount of solar energy penetrating the atmosphere is significantly attenuated), and the basic stability of such platforms. Given that the resources available in the Venus atmosphere are also available elsewhere (in comets and icy asteroids) I don’t see a pressing reason to do this at this point.
Astronauts are obviously smarter and generally more adaptable than robotic probes (at least at the current state of the art) but all of the protective systems required to keep an astronaut alive and healthy place a lot of restrictions on what he or she can actually do; witness . In addition, instruments and tools have to have human-usable interfaces (consoles, display screens, handles, et cetera) which increase size and failure points whereas tools integrated into probes tend to be very compact and robust.
However, robots are not good at performing very generalized tasks such as repairing machines, analyzing data, setting up and observing open-ended experiments, et cetera. Anything that requires abstraction or judgment beyond what can be built into an algorithm is and will probably remain beyond the domain of automated machines for the foreseeable future, and there are many task for which remote operation is awkward or insufficient. However, most of these tasks do not require that a person be send into and protected from hazardous environments.
In simple terms, just stowage space and power. The cost isn’t really sending these supplies with a crew on an interplanetary voyage, but just getting sufficient supplies up into orbit, along with a vessel to transport them. The greater hazards are radiation, hygiene (a freefall environment is one of the most unhygienic environments imaginable by virtue that all contaminants, wastes, and ejecta float around rather than fall onto an easily cleanable surface), social isolation, and reliability of life support systems that are absolutely required to function for the entire mission duration.
Stranger
Aha, that makes much more sense to me, thank you. I wasn’t visualizing that the collector shaded the structure. And I get the difference between those two discussions now that you point them out: your issue about dumping heat from the generation ship was related to drive attached to it, which isn’t the same situation here. Got it.
I’m still a little vague on the overall shape of the structure. You start with a sphere, and end up with something egg shaped. In one of your examples above, you said, “4 km in diameter and up to 12 km long”. I’m assuming “in diameter” means perpendicular to the spin axis, and “long” means the length of that axis, correct? So we’ve got (so to speak) an egg standing upright, spinning like a top, with a pie plate (the collector) attached to its’ top surface, and the sun directly above, so the pie plate keeps the egg in shadow. Is that about right? I’ll have further questions about the shape, but I wanted to make sure I had that much right.
ETA: obviously my egg + pie plate has the scales between the two mismatched. Imagine a pie plate the diameter of the short dimension of an egg. Or an egg so big that it’s short dimension is the diameter of that pie plate.
Correct, the structure rotates about the long axis so that it is symmetric. The shape of the structure can be controlled by the way it is reinforced and expanded; a spherical shape for the initial structure is selected for simplicity, but an ellipsoid for the final structure is assumed for stability and strength.
Stranger
One thing that strikes me; if this habitat is in tension due to tidal forces on the counterweight, it will face the planet it is orbiting rather than the Sun. Unless the habitat is orbiting the Sun directly, you’d need some other arrangment to keet the solar collector pointed at the Sun.
I would expect a large habitat to be solar orbiting (or essentially in solar orbit at a libration point) but if it were orbiting Earth or another planet, you are correct; the solar array would have to be actively oriented toward the Sun and the long axis of the habitat redirected parallel to the orbital axis.
Stranger
Hmm; this is interesting. If the cylinder is oriented because of tension from a tether, there will be another force acting on the inhabitants (and the lakes) inside the cylinder in the opposite direction, so that water will tend to flow towards the sunward cap.
Since the cylinder is actually eggshaped rather than cylindrical, the water will form a slight cone inside the habitat; a very intriguing environment to live in, I think.
I bet you can see where I’m going with this: how does the egg get egg-shaped along the spin axis? You describe a sphere, slowly spinning, that gets material added, is reinforced, then is spun faster, which causes it to grow and more material/reinforcement is added as it does. I’d think you’d end up with a oblate spheroid spinning around its short axis – what encourages it to get “taller” rather than squatter as it gets bigger? Obviously you have a mechanism in mind, but I don’t grasp it from your description.