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Tom,
Please allow me to suggest a few options.
Divide the device into at least two layers. A top layer (O2 dominated), and a lower layer (H2) dominated.
Although this suggests that the device would tip over, it would not be so, if you used life support equipment and supporting members as ballast.
The primary reason I suggest is that the Layer of Hydrogen below, would push up on the floor, which because of that could be made lighter. Humans walking on it of course should have footwear that would be gentle to the floor, that would be prudent.
I know that now it would seem that I suggest a very scary situation, a H2 compartment with a wall separating from an O2 compartment.
However, I would think it would be wise to provide for a felt like "Wick" material, which would allow any leaking gasses, particularly H2 to drain to atmosphere. The "Felt" being interposed as a layer between the O2 and H2 compartments.
In fact that could be improved, by closing it to atmosphere, and filling that layer with a non combustible gas, such as CO2, or raw atmosphere which is CO2 with a bit of Nitrogen. In emergencies, a purge gas still could be pumped into that "Felt" layer, to vent H2 to the atmosphere. The purge gas would likely be raw atmosphere.
While Hydrogen would tend to leak slowly from the H2 compartment into the "Felt" layer, that content of H2 could be kept well below the Explosive or Flammable limits, I presume by using a centrifuge to remove it and return it to the (Primarily H2 chamber).
As I see it then the upper bubble could support O2 producing Photosynthesis, and the lower could support H2 producing Photosynthesis.
Biological Hydrogen Photosynthesis:
https://en.wikipedia.org/wiki/Biologica … on_(Algae)
I think some work might be required to breed a very successful version of the Algae, but it would be a useful thing if it did work.
As for light in the lower section, it is reasonable that it would be supplemented by reflection from the cloud deck.
So then your "City" would potentially be quite light weight, and would provide solar energy, which could be stored as compressed gasses, in the Hydrogen area, at least for the Hydrogen. (Those tanks serving as some of the ballast).
And of course you would be using fuel cells to generate your electricity.
I leave for dealing with heat, your methods may be good, radiators being ballast to keep the city upright, or it may also be reasonable to consider "Shades" to supplement that.
When setting a short term objective, I would prefer to look at the long term potentials. In the case of the Norse Greenland colony, strangely, even though that group of Norse, would sail the north sea, they would focus on finding sheltered fjords where they could farm.
https://en.wikipedia.org/wiki/Fjord
They liked it that way, and that is how they may have lived in Norway prior to Iceland.
However, if I have the story right, they did not seem to be interested in fishing, or catching sea mammals.
I would defer to more traditional "Greenhouse" methods for sure, as a start of a settlement, particularly if that is something that can be well rehearsed and simulated prior to a mission.
But I will say that most of the thinking I notice about Mars seems to indicate people have a mind set that it is going to be like the South West of the North American continent. It looks like it to a large degree, but in reality it is much more like the dry valleys of Antarctica.
To also rehearse what methods would be well suited to Mars as it really is, is not wrong.
The reality is that Mars at it's best will likely be a poor relative of our higher latitude areas even after terraforming. That is not to say that humans could not have a prosperous existence there, but the price for that will be mostly technical adaptation and the manipulation of large amounts of liquid water.
The lessons of those lands, especially at the highest latitudes are that life prospers more in bodies of water than on the land at the same temperatures.
So indeed the mission(s) have to be focused on what is possible, but if they do not lead to a solution to harmonize with what Mars actually would be willing to give to the human race, they will be a waste of time, except for scientific discovery, I suppose.
Further, I am more optimistic than is typical here.
I see NASA is focused on asteroids, since the inhibitors forbade them from actually doing anything else.
Private concerns are approaching the ability to launch items such as the Bigelow expandable modules into space.
It looks like there could be new propulsion systems started, and improved in the next 5-10 years. For instance perhaps the Vasimr.
So, as a mission to Mars is likely still fairly far off, I do not feel restricted to the present available hardware, or it's directly similar devices alone.
And honestly I would have preferred that you comment on the posts I made, instead of trying to bypass them.
As a supplement to the last post I made, I can point out that any terraforming scheme involving greenhouse gasses would likely first release the CO2 deposits in the polar ice caps. Particularly the one in the South polar cap. According to my reading, that would elevate the average pressure on Mars to 11 mb, and reportedly that would be enough to allow for snowfalls, and melt water, and temporary streams, so it is likely that during any such terraforming scheme, an approximation of Antarctic conditions of the dry valleys would be achieved rather early, and very likely natural forces would begin to build such lakes.
However further human interventions to promote their formation would make a lot of sense at that point I would think. Methods such as ice block coverings, and diversion of temporary streams of melt water into the lakes, before they evaporate.
What you would hope for Tom would be something like this:
http://phys.org/news/2015-09-oxygen-oas … earth.html
They occur in Antarctica.
I am not going to say that there are none on Mars, but I don't think they could exist naturally in the present climate. Primarily, because of a lack of melted make up water. You have suggested ground water, but we don't have strong reason to suppose that exists from what we think the conditions are on Mars.
In Antarctica, for a few weeks in the summer, warmer temperatures, and constant sunlight can melt small rivers/streams. This flow ends up on top of existing lake ice (Often), and the weight of the water relative to the ice causes the ice to crack, and the water flows through the cracks into the water reservoir below the ice. This process must add enough water to replace water evaporated from the ice surface around the year.
The other factor that allows these lakes to exist is the solar pond effect. Salt accumulates in these lakes. However, the layer on top is colder, but less salty. This could be in part because fresh water gets added to it each summer, but also could be a factor of the ice thickening over the long winter, and expelling brine (To sink to the bottom of the lake), in the summer, I would presume that solar heat causes the bottom layer of ice to tend to melt, releasing a less salty water.
The upper less salty layer also supports photosynthesis, which produces oxygen.
The lower anoxic layers are saltier, and warmer, and can for instance be around or above room temperature. This is from solar heat.
I think that a Mars like world might just be able to support a similar lake, without the existence of summer running water.
In that method, a glacier would dump ice directly into the lake, to encounter the salty anoxic warm layer, and that method would add water to replace evaporated water. Just possibly this has occurred on Mars at the Equator, if the planets axis were extreme.
Artificial lakes:
If you are going to create a lake of this kind, it presumes that you will cause water to be added to it as needed. This is a problem because the evaporation rate would be very high.
A mechanical method is needed to protect the otherwise exposed ice surface. Several options are possible.
However I am going to suggest that in the end the lake be covered with "Blocks" of encapsulated ice, over the normal ice layer.
So, however you might start to have a lake, if you wanted to expand it, you would add water to its body, and the water would cause the ice to lift up. Then the edges of the lake would have exposed ice. You would bring a transparent plastic bag out to a bare patch, and place it over the bare patch. Then you would quickly fill it with fresh clear water, through a port. You would wait for the water added to freeze, and then seal the port. A bubble of air would remain in the plastic bag, but the bottom of the bag would be covered on the bottom with a layer of rather transparent ice as thick as desired. You would also put a epidermis layer over this whole assembly. That layer would be to protect from U.V. light, and like your outer skin would be replaced as it deteriorated from "Weathering". This will also tend to shed the heat of the U.V. radiating it away into the atmosphere, keeping the ice blocks below cooler.
The bag(s) would only have to hold a peak pressure of a few mb above local ambient, so during the Martian day, due to that pressure retention, and thermal inertia of the block of ice, I believe that stability would be maintained. In fact, I think that block of ice could be so cold from the nighttime temperatures, that very little pressurization would occur at all in the bag, from vaporization of water.
It would be important to build the encapsulated blocks of ice so that they do not absorb very much light, and so do not heat up from solar energy themselves.
Of course I am talking about a tile surface over the normal surface ice of the lake, a horizontal assembly of multiple blocks. The tiled surface would impose pressure over the lower "Normal" ice layer, and so greatly reduce evaporation from the lake. If necessary, the "Cracks" between the tiles could be caulked with something I suppose, but it may not be necessary. The cold of the ice in the bags would also transfer to the underlayment ice, and so discourage vaporization.
So, if you have this impoundment of water, a reservoir that is exposed to visible light, this might promote the habitation of Mars, even if the only life in the lake were microbes. However, using solar concentrators under the ice, I think it may be possible to grow more advanced plants. Easiest would be fully submerged pond weeds (Domestication will be a problem). By solar concentrators, I indicate that the light getting through the ice may be attenuated more than what is needed for the plants, so you would build a solar concentrator which would be in the water, under the ice, and which would shine concentrated light on your subject plant.
Such devices could be attached to cords, to the warm bottom below. Humans would be in a room temperature environment, and might pull those down temporarily to the bottom to plant and harvest them. Obviously they would want to harness Oxygen in the colder upper layer.
So, then the source of water. Glaciers perhaps, but how about the polar ice caps themselves? In fact it might be reasonable to have very large impoundments from such a large reservoir of water.
Another thing about considering living on the bottom of a lake/sea/ocean on Mars. If your building leaks, it leaks water in, and air bubbles out.
There should often be time to remedy the situation, or evacuate to another building, swimming in warm bottom water with just breathing assistance.
On the surface, at the air pressures currently existing, an equal sized leak would instead quickly lead to death producing conditions, and the chances of remedy or evacuation would be rather small.
Solar energy? Well, some studies indicate that even now there should be significant exposed ice, where sunlight melts small pockets of melt water (Contained by the strength of the surround ice, not a ice/water column). So, it is not that wild an idea.
However, I am going to bet that in about 100 years or less there will be fusion power, and indeed plenty of power to power a Martian colony, and it's waste heat could be dumped into the polar ice caps, to indeed build Lakes, Seas, and perhaps even Oceans, with an Oxygen layer long before the atmosphere will ever have significant Oxygen.
Very good of you to do the work for me.
I see that ice is perhaps not the preferred method, since water is plentiful (If you can reach it) in the Oort Cloud/Kepler Belt.
The ice layer, is a sort of water conservation notion, but since they could indeed build a strong metal shell, why not?
As you have indicated, why not have a more pleasant "Radiator". I might speculate that the surface of the sea could have as much "Land" as you choose to make. (Land just being a large variation on a boat/barge.
Nice.
Is that a Pingo on Ceres?
http://blog.sfgate.com/science/2015/08/ … net-ceres/
They beat me by 4 days.
I would like your thoughts on translating your plan for Amalthea to the object in this article (Kepler belt object 48 km / 30 miles in diameter.
http://www.space.com/30415-new-horizons … arget.html
For my part, I would hope to use your shell method, a very tenuous atmosphere, and an ice shell over a melted ocean, as the end product.
Also, I might hope that a bubble of air could be enclosed at the center of the sea. Inside that bubble of air could be artificial gravity devices. I am both lazy and really not that interested in doing the math, if I can get you to.
What could the bubble size be?
How deep would the sea be?
Obviously this will require a power source such as fusion.
The method if accomplished should be relatively stable, except if your bubble should develop a air leak into the sea, with sea water leaking into the air bubble. But that is a curious matter, would the center of gravity be within the sea? Then it would be a spherical center of gravity. I suppose it would depend how much solid matter was inside the air bubble.
It's hard to wrap my mind around it, which is sort of fun.
So, where are you these days Impaler?
http://phys.org/news/2015-08-artificial … cient.html
Quote:
A critical component that contributes to the efficiency and safety of the new system is the special plastic membrane that separates the gases and prevents the possibility of an explosion, while still allowing the ions to flow seamlessly to complete the electrical circuit in the cell. All of the components are stable under the same conditions and work together to produce a high-performance, fully integrated system. The demonstration system is approximately one square centimeter in area, converts 10 percent of the energy in sunlight into stored energy in the chemical fuel, and can operate for more than 40 hours continuously.
Read more at: http://phys.org/news/2015-08-artificial … t.html#jCp
Quote:
"Our work shows that it is indeed possible to produce fuels from sunlight safely and efficiently in an integrated system with inexpensive components," Lewis adds, "Of course, we still have work to do to extend the lifetime of the system and to develop methods for cost-effectively manufacturing full systems, both of which are in progress."
Read more at: http://phys.org/news/2015-08-artificial … t.html#jCp
So, as far as I am concerned, this could be quite better than trying to grow bulk vegetation in a pressurized greenhouse on Mars.
If it works then the device using cold fresh water might not have to be pressurized very much.
Further two other further out there options would be.
Run it on cold brine. In that case the greenhouse (Transparent Glaze) does not have to be pressurized at all.
Or; if it could run in a pure water vapor atmosphere, then the Transparent Glaze enclosure would not have liquid water in it at all, but a water vapor dominated atmospheric mix.
Therefore from one or more of such variations, a source of fuels, and chemicals to drive Chemosynthesis.
In my opinion greatly reducing the problems of the initial establishment of settlements on Mars.
Nasa seems interested in the VASIMR
http://nasawatch.com/archives/2015/08/n … d-ast.html
For what it is worth;
I know that Bigelow has been waiting for LEO launch vehicles, otherwise they were ready quite some time ago.
Because of this and also because of the potential advances in propulsion that you have brought up,
and because of Musks intentions for Mars,
I do not think NASA's hardware is as non-adapted as it might seem. They were in a crippling situation, but the whole collection of developments might actually get the human race moving to Mars and elsewhere.
A little modification there:
https://en.wikipedia.org/wiki/Colonizat … m#Callisto
Quote:
Callisto[edit]
Main article: Colonization of Callisto
Due to its distance from Jupiter's powerful radiation belt, Callisto is subject to only 0.01 rem a day.[6] When NASA carried out a study called HOPE (Revolutionary Concepts for Human Outer Planet Exploration) regarding the future exploration of the Solar System,[11] the target chosen was Callisto. It could be possible to build a surface base that would produce fuel for further exploration of the Solar System.
For me that is a good thing, because it might be possible to generate power from Callisto's orbital inertia vs Jupiters spinning magnetic field.
It would be a good base to start off with Jupiter anyway. It is possible that the radiation belt will be modified some day, there have been speculations on how to do that. As I recall, it might have come from a Russian. The notion would be to have an orbital device that would eject the molecules from the radiation belt. That's all I have though.
Having habituated Callisto, and having at least one "Shell" world in it's gravitational tow, I would think the inhabitants would always be searching for a method to move inward, perhaps next to Ganymede.
Also, I do agree with you that there is a mysterious method where volatile substances seem to hold where they should not. I do not dispute what you have said, since I don't have any better information.
But I also ask about electrostatic charge. If a (+) or (-) charge were left behind lets say a fraction of an inch or meter, it is not impossible that that would be attractive enough to try to retain evaporated molecules, forming a thin skin of vapor over a dirty, organic, salty, ice.
How this could occur, I do not have enough information, but if the solar forces selectively stripped away a (-) or (+) charge from evaporating gasses, then the remnant would potentially be of an opposing charge to the charge just under the surface of the "Ice".
I did not comment on the mountain, because I don't know how it formed. A wild guess would be cryovolcanism, or perhaps it was a relatively more icy block that floated up in a "Sea" of heavier mud-ice. Then it would have eroded into a cone, sort of. But if that were the case, then it should have shed a bunch of dirt as the ice vaporized it into a cone, and that dirt should deposit at the base of it.
Just on the side,
I think if you did have a Hydrogen balloon, and imposed a minus electrical charge inside of it, and a relative plus electrical charge outside of it, you might be able to encourage wayward Hydrogen atoms trying to escape through the pores to stay inside that balloon envelope.
Obviously you would not want such a charge magnitude that it would burn holes in the balloon.
This device would also serve as a capacitor, for what that is worth. Not a very strong one however.
If it were me, I would consider an envelope containing N2 or HE, and inside of that multiple Hydrogen envelopes.
I am sure that for Venus, every trick in the book will have some use at some time for some purpose, as far as lighter than "Air" methods go.
The story I have read about why Vesta and Ceres are different, is that Vesta formed before Ceres, when the radioactive elements had not decayed as much.
Such as:
http://starplan.dk/news/heterogenous-di … lar-system
Of course I am not an expert.
Anyway it is thought that Vesta would have heated up much more from radioactive decay than Ceres, and so the ices would have vaporized off of it. But that is just a story.
I open myself up to egg on the face again, but I do think that salt could be involved in slowing down evaporation. Some salt will be there no matter what. How much it might help to slow down evaporation I cannot say.
If Ceres were like a comet, then for the spots, I might venture to speculate that actually there vents that entend to the subsurface. What the bright spots are, condensate or residual salts, I cannot say.
I clearly understand you are trying to find a way, even though the Jupiter system, especially the inner Jupiter system, is more or less some of the "Badlands" of the solar system.
I would make another alternative suggestion, that for Calisto itself, it may be possible to shape groves in the ice to be 1/2 concentrating mirrors, think of a long concave mirror, cut it in half, and from the bottom raise a wall almost strait up. Make this of ice, put a reflective foil on the curved surface. Then at the top of the wall, put a collector. As Calisto has a fairly strait up axis, it should be possible to have the concentrated light impinge on the wall, and there to place a greenhouse. Such groves, being as trenches which could encircle the moon, switching to a new one as you move up sufficiently from the equator to a higher latitude.
Anyway, therefore using the little moons gravity for what it is worth, and concentrating it's light without have complex machines of metal with giant bearings.
Of with your method for small moons, deal with a small asteroid with water. Some of the smaller ones have comet tails.
But you knew that easier targets are available. I think that while it is fun to speculate on how to overcome a hard problem, it is likely that there worlds that we should forget about ever habituating, such as Jupiter itself. The Oort cloud will most likely provide a massive alternative to some of these nasty situations long before it becomes realistic to even try to deal with them.
Helium
http://www.ncbi.nlm.nih.gov/pubmed/17831413
Helium is removed at an average rate of 10(6) atoms per square centimeter per second from Venus's atmosphere by the solar wind following ionization above the plasmapause. The surface source of helium-4 on Venus is similar to that on Earth, suggesting comparable abundances of crustal uranium and thorium.
Could you drill wells for it? Harsh environment for that, so I suppose you might extract it from the atmosphere, which would be expensive. I really didn't think that floating habitats were going to rely on Helium anyway, Air gasses, such as N2 more or less? But if you could have helium bubbles inside of your main N2 bubbles, perhaps it could be worth it, and you might be able to recover Helium spills, because they would still be contained in the N2 bubble.
But then again that offers a solution for H2 leaking through it's containers. If H2 bubbles were inside of a main N2 bubble, then I would think a centrifuge might allow you to recover much of the H2 leaking into the N2 bubble, and recycle it back into the H2 bubbles before it leaked through the N2 bubble wall. Plus the barrier between the CO2 atmosphere and H2 bubbles provided by the N2 would be an extra safety margin, even though it is rather hard to ignite a fire of H2 and CO2.
I think you did some very good thinking on the tower thing for Venus, and I agree with the points you have made that I have noticed, with a possible exception of UV protection, but there I might be wrong.
I would say the UV protection might be the best at the poles, but I am not sure that it would be "Great".
But nice work.
Perhaps a literal ping pong ball, but if you can make a floating city float on Venus, then I am sure you can create a sphere of material an fill it with Nitrogen and it will float. It just depends on the mass of the shell vs the displacement volume of the "Ball". Larger I believe will hold more displacement volume per mass of shell, then smaller. And then also it may be that the shell itself can be of lighter construction, but if using a strengthener like Carbon fibers, could be sufficiently strong to have a sufficient working life. I am actually thinking that it should be made of materials mostly from the atmosphere itself.
As I say, if you plan to make a city float with people and their life support, I am sure that you can make "Fiber reinforced" "Plastic Balls" (Or other shapes) float in a CO2 atmosphere.
I used ping pong ball as an illustration, and wanted to convey the notion that if they bumped into each other at reasonable forces, or a floating city or a tower, they should not cause significant damage, with would be an attribute I would think is desired.
If this were to work, and the UV problem were overcome, and also the acid nature of the clouds was within the survival range of some Cyanobacteria/Algae, then the total light impinged area would be enormous (Supposing the clouds were loaded with them around the planet).
The clouds should diffuse the light, so that it scatters, and tends to imping on all surfaces of the balls.
A potentially huge biosphere I think, and the organic result should be usable to build a food chain, and plastics industry. Possibly Carbon extracted by destructive distillation could be stored on the surface, perhaps buried under soil, thus freeing up some additional Oxygen. (Which may or may not form Ozone or CO). In either case it could be a useful alteration of the atmosphere of Venus.
Some additional topics here:
https://en.wikipedia.org/wiki/Space_medicine
A bit more on radiation:
https://en.wikipedia.org/wiki/Space_med … on_effects
For radiation, though, that's about it.
But An ounce of prevention is worth a pound of cure" it is said, so, I think that actually you could call radiation shielding preventative medicine.
Sleep disorders:
https://en.wikipedia.org/wiki/Space_med … _disorders
I am thinking a temperature controlled chamber of a hydrocarbon liquid (Which can also be a fuel). Actually a tank with an opening the body can be inserted into, with a liquid tight sack that might serve like a sleeping bag. A domed hinged lid over the entrance port. A sensory depravation chamber so to speak.
If that doesn't work then; A soothing quiet music, may help to prevent the mind from ruminating which is usually what keeps me up.
And in spite of what the article says, as a last resort; If that doesn't work, then resort to a movie you have seen 20 times, or something like last of the summer wine, which also can put me to sleep.
This thread is doing much more that I thought it would. Yes, since you need water, and eliminate watery fluids, why not use that as shielding also.
For the design Robert, will the information I have referred to below seem to reduce the overall weight needed? NASA appears to be working on some very interesting things according to what I read.
http://www.projectrho.com/public_html/r … iation.php
http://www.nasa.gov/vision/space/travel … lding.html
Polyethylene is a good shielding material because it has high hydrogen content, and hydrogen atoms are good at absorbing and dispersing radiation. In fact, researchers have been studying the use of polyethylene as a shielding material for some time. One of several novel material developments that the team is testing is reinforced polyethylene. Raj Kaul, a scientist in the Marshall Center's Engineering Directorate, previously has worked with this material on protective armor for helicopters.
The combination of heat and pressure causes the chemical reaction that bonds the layers together to form a brick weighing about half as much as a similar piece of aluminum.
So, maybe it is a magic material for building things on Mars, a desired primary technology for Mars.
Traveling in space is not the same as surviving a nuclear war, but perhaps this article has merit for space travel anyway, perhaps especially if people experience high radiation from a solar flare.
http://medicalxpress.com/news/2015-08-d … hours.html
New drug protects against the deadly effects of nuclear radiation 24 hours after exposure
For the problem of UV light on Venus AND MARS, perhaps what is in this article.
http://solstation.com/life/ven-life.htm
In 2004, Schulze-Makuch and his colleagues announced their speculations that such microbes may survive in Venusian clouds with the help of molecular rings of sulphur to shelter from the Sun's ultraviolet (UV) radiation as Venus does not have a protective layer of ozone in its atmosphere. Patterns of absorption in the UV spectra of Venus suggest that its atmosphere may contain lots of "cycloocta-sulphur", molecular rings of eight sulphur atoms. Such compounds double bonds that readily absorb UV light, then re-radiate the energy at relatively harmless visible wavelengths.
Doing that, perhaps some type of Cyanobacteria could be caused to grow on either planet, even in early stages of terraforming, when little or no UV protection was available. Martian soils tend to contain significant Sulfur I believe.
Of course I am thinking of the ping pong balls which might float in and be moistened by the clouds of Venus.
I'm not prepared to vouch for life on Venus (Clouds), but an interesting read.
http://solstation.com/life/ven-life.htm
What I am after is;
(such as hydrogenogens, diverse bacteria and archaea that grow anaerobically utilizing CO as their sole carbon source and water as an electron acceptor to produce carbon dioxide and molecular hydrogen as waste products).
So anaerobic matts where hydrogenogens is present.
http://www.ncbi.nlm.nih.gov/pubmed/22011721
So this is another twist, separate CO and O from CO2 using a process such as in the previous post, and have lower pressure greenhouses with algae matts. Feed the hudrogenogens water and CO, and it produces Hydrogen for you.
Feed the algae matts to fish as well. Use some Oxygen to let them breath.
Supposed better method to split CO2 into CO & O:
http://phys.org/news/2015-08-porous-mat … oxide.html
Organisms that might eat CO and breath O2:
http://www.popularmechanics.com/space/m … -monoxide/
So I have always wondered about the lack of interest in Chemosynthesis for Mars.
https://en.wikipedia.org/wiki/Chemosynthesis
I don't see it as a complete substitute. Greenhouses with Photosynthesis are also desired, and also just gardens to amuse humans.
So, as I see it if you have a power grid, and it is large enough to supply the peak power demands, and perhaps have a bit more in case of damage to the system, during off peak times that energy could be used to split CO2.
This would provide you with potential food, and a feedstock for fuels and plastics.
It would also reduce the amount of transparent "Glass" that you would need. That is always vulnerable and expensive in my opinion, since it generally has to withstand differential pressures of significance, and not leak significantly. It is also a source of thermal variations. Heat loss at night, and overheating during the day (Potentially).
I see both points. I am intruding again.
undormant:
Atmospheric loss is considered a loss, but where does it go?
Does it to the outer solar system and condense onto objects there? Or leave the solar system? Maybe some of each. So comets from whatever location are potential sources of replenishment of atmosphere, but it requires energy and time, and a method to manipulate the objects.
Something has to cause the objects from the outer solar system to "Rain" down on the "Dry" objects in the inner solar system.
In the distant future, if humans or other inhabitants of a solar system, were to know what the secrets of Dark Matter, Dark Energy, and Gravity are, then perhaps they could work to "Water" the inner solar system with outer solar system objects.
But for now, I agree, that worrying beyond even 500 years is more than we should care about just now. Mars will last more than 500 years if partially improved with it's local materials. Venus may be habitable with partial alterations.
Shell worlds being in a gravity tow of a moon (To generate electrical power from an outer planet magnetic field) should be possible. That's quite a lot.
RobertDyck:
https://en.wikipedia.org/wiki/Volcanology_of_Io
https://en.wikipedia.org/wiki/Sulfur_dioxide
SO2 Boiling Point: −10 °C (14 °F; 263 K)
So that's somewhat lower than water. If the moon were covered with water (And a ice layer) the water would be a bit less explosive than SO2
So if you were these way in the future "People" who could manipulate vast numbers of comets to "Water" IO, perhaps you could covert it to a Europa over time (But a Europa with much more energy).
To bleed off heat, perhaps you would target comets, to directly poke into hot spots, and make them explode and dissipate energy, causing an overall temporary loss of the moons heat overall. The you would have to keep the bombardment up, until you had a water layer / ice layer / temporary atmosphere layer thick enough so that explosive volcano's could not eject too much material into space. And the conversion of the moon to a liquid water cycle could take some time.
Really very far from our abilities, or what we might hope would become "our" abilities for thousands of years, I am guessing.
And I have ignored radiation.
I believe that the surface of IO warps about 6 feet? (Dim Memory) with the tides. I would think the water/ice/atmosphere would warp also, and so, if you really did do this an choose to inhabit the moon, your best location would be on the top of the ice shell, but you would have to compensate for that, and you might also have earthquake driven tsunami that would certainly make living on the ice shell "Interesting".
As an alternative, perhaps you would opt for a very deep ocean, no ice shell, and a very thick atmosphere, and live in cities floating in the atmosphere.
I think this makes entertaining material for fiction books, but would much rather deal with Mars, Venus, Luna, Ceres, Calisto, and Titan as far more realistic.
Well that is a choice Tom, if the asteroid is not a rubble pile.
One interesting variation would be to have the asteroid crash into the supercritical part of the surface of Venus. Just possibly this would process some of the asteroid, extracting minerals, and then condensing them elsewhere.
Antius, Yes, I see your method. Saturn might be a good place. Lots of small icy moons, but you would also perhaps want some Metal/Stone asteroids. Use Titan to tow the shell though the magnetic field, and as a source of Plastics & Nitrogen.
Of course if Fusion power ever arrives, then you have a ticket to move all the way out, even to the Oort cloud and beyond.