Quote from: uhuznaa on 10/14/2016 10:37 amAlso a few feet of regolith on top won't help much against an atmospheric pressure of 10 tons per square meter trying to push things apart from the inside. You'd need to pile 10 tons of regolith per square meter on top of your building to counter the atmospheric pressure inside. Regolith has a density of about 1.5 g/cm^3, so in Mars' gravity this would be a layer of 20 meters (about 65 feet) thick. Only if you would add even more on top your structure will start to come into compression and you'll start to need arches, columns etc. Until then it is under tension and will try hard to explode from the inside.1.5g/cm^3 means 1.5t/m^3. So more like 6.67m thick for 10t. Mars gravity is only 0.38g, so more like 17.54m. Maybe it would make sense to reduce the pressure in the hab.For a bigger habitat the excavated regolith for the cover will be smaller relative to the total excavated regolith. So I think bigger (or better deeper) is better. In theory.Edit: Ups, corrected.
Also a few feet of regolith on top won't help much against an atmospheric pressure of 10 tons per square meter trying to push things apart from the inside. You'd need to pile 10 tons of regolith per square meter on top of your building to counter the atmospheric pressure inside. Regolith has a density of about 1.5 g/cm^3, so in Mars' gravity this would be a layer of 20 meters (about 65 feet) thick. Only if you would add even more on top your structure will start to come into compression and you'll start to need arches, columns etc. Until then it is under tension and will try hard to explode from the inside.
On one side is a rock wall sculpted with broad terraces and balconies connected to habitations extending a thousand feet up to the distant roof. It looks out into a space extending kilometers that is so vast it seems like an outdoor landscape. The floor is parkland that includes forrests and lakes. Towers as tall as 100 stories with broad balconies that offer landings for flying cars rise in the foreground. Some structures hover in mid air suspended from the roof. Architecture is fanciful and creative, liberated from earthly constraints of weather, geological instability and high gravity. Flying cars, safe because they're autonomous, are much more efficient than on earth. In the distance at night is a panorama of lights embedded in the ice face as an art project, seeming like an arc of starry night sky.Unlike an O'Neill space colony, it grows organically in place, inhabited the entire time. It didn't have to be planned in every detail and completed before it was habitable. It's a more ordinary city in that respect.
You can reduce hab-pressure slightly, but not by much. Or you will have to go up with the oxygen ratio, which comes with its own problems. There are good reasons for staying at Earth-like atmospheric pressure (like on the ISS).
If you are trying to melt ice for its water, (and to make a habitat bigger) one advantage of an ice habitat is that any waste heat can be used for that very thing, melting ice in new areas. You just have to find a very efficient way of moving the heat to where you need it.I'm not sold on this idea but I did want to point that out.
3/4 atm is also very good. Basically what planes pressurize to. Also almost nobody can feel the difference at the equivalent 7000-8000 foot altitude. (if I got my numbers right)
Quote from: rsdavis9 on 10/14/2016 04:18 pm3/4 atm is also very good. Basically what planes pressurize to. Also almost nobody can feel the difference at the equivalent 7000-8000 foot altitude. (if I got my numbers right)If I got my info from diving right it would be slightly too high for getting into spacesuits without pressure adaption. Otherwise right, really no need to have full sea level pressure, every reduction helps. On the ISS full pressure has advantages in transfer from and to earth. Not an issue for Mars.
Keeping O2 partial pressure equivalent to sea level at 1/2 atmosphere would be at 40% O2. Dropping O2 partial pressure to about 8000 foot (2400 meter) equivalent at 1/2 atmosphere would be 30% O2. That should work just fine for spacecraft or a Mars colony.
Best keep pressure at sea level. There are enough unknowns with the low gravity and high radiation.
I agree 4000m is a little extreme.OTOH 3000m is much more doable. 10000 feet.The grand canyon rim is about 9000 feet. Probably a little less.EDIT:I was way off 6800 feet for grand canyon.
Quote from: Impaler on 10/14/2016 04:13 am90 percent of the glacier-cave talk here sounds like it's been lifted strait from the Zygote settlement of the Mars Trilogy. The notion that a cave itself can be a pressure vessel is deeply flawed, the rock that a glacier sits on can easily be fractured and allow air to escape, as the habitat air is warm it can cause sub-surface melting, likewise the interior air in the cave would have to be kept away from the ice roof to prevent all the issues I described earlier. The net effect is that your going to need to have a full top and bottom pressure envelope inside the cave, it can be thin because it dose not need protection from micrometeorites as it would exposed on the surface but the cave is really not doing anything that a architectural dome and a few meters of regolith couldn't do, and it has disadvantages too, susceptibility to creep over time, difficulty in dumping waste heat as have been mentioned, inability to use skylights or any other top-down access to the habitat area. Probably most important is that it requires that you not perform simple surface mining of the same glacier body that your living in so as to avoid damaging your own habitat.Construction on the surface with arches, vaults, columns and other compression load bearing structures can provide the necessary radiation protection without any of these issues. The same thin membrane pressure vessels inflated inside these protected spaces will be necessary but this is unavoidable and a wash. Also note that some posters have erroneously claimed that a single massive pressure vessels is more efficient then many small ones, this is a common error in thinking that the pressure vessel mass scales only with surface area, in actuality it scales with volume due to a large vessel needing a thicker wall. Given the inherent danger, I would say death-trap-ishness, in a single pressure vessel the interconnecting of many individual pressure vessels is certainly the way to go.Note that a livable habitat is going to consist of a LOT more mass in equipment, life-support and otherwise beyond the pressure vessel, even a pressure vessel made 100 percent from local materials will need nearly the same amount of vital equipment to shipped in. This is the flaw in most space-cadet style housing solutions, they pretend that they are making log cabins in which just walls and roof are all that's needed and that they are saving 90 percent of the shipment mass from Earth.I think you're confusing pressure vessels with making things gas-tight. "Arches, vaults, columns and other compression load bearing structures" won't help at all because your building will not be under compression at all. It will be under tension. The atmospheric pressure inside will try to push things apart form the inside.Also a few feet of regolith on top won't help much against an atmospheric pressure of 10 tons per square meter trying to push things apart from the inside. You'd need to pile 10 tons of regolith per square meter on top of your building to counter the atmospheric pressure inside. Regolith has a density of about 1.5 g/cm^3, so in Mars' gravity this would be a layer of 20 meters (about 65 feet) thick. Only if you would add even more on top your structure will start to come into compression and you'll start to need arches, columns etc. Until then it is under tension and will try hard to explode from the inside.Cracks in rock in a cave or tunnel aren't a problem, a thin membrane to prevent gas from escaping is easy, but there is no such thing like a "thin membrane pressure vessel". In a cave the pressure would be countered by the weight of the rock above and around it. If you don't have that weight you have to counter the pressure by tension in your pressure vessel and this not going to be a thin membrane then or bricks, or anything short of steel or aluminum, or massive reinforced concrete. And yes, you need more than just pressure vessels to live in, but they're the biggest things you need and if they fail you won't have any time to fix things, because you will be dead immediately. They are the first and most crucial thing you need. And if you want to live and grow food in them, they need to be big and you need many of them and they need to be safe.
90 percent of the glacier-cave talk here sounds like it's been lifted strait from the Zygote settlement of the Mars Trilogy. The notion that a cave itself can be a pressure vessel is deeply flawed, the rock that a glacier sits on can easily be fractured and allow air to escape, as the habitat air is warm it can cause sub-surface melting, likewise the interior air in the cave would have to be kept away from the ice roof to prevent all the issues I described earlier. The net effect is that your going to need to have a full top and bottom pressure envelope inside the cave, it can be thin because it dose not need protection from micrometeorites as it would exposed on the surface but the cave is really not doing anything that a architectural dome and a few meters of regolith couldn't do, and it has disadvantages too, susceptibility to creep over time, difficulty in dumping waste heat as have been mentioned, inability to use skylights or any other top-down access to the habitat area. Probably most important is that it requires that you not perform simple surface mining of the same glacier body that your living in so as to avoid damaging your own habitat.Construction on the surface with arches, vaults, columns and other compression load bearing structures can provide the necessary radiation protection without any of these issues. The same thin membrane pressure vessels inflated inside these protected spaces will be necessary but this is unavoidable and a wash. Also note that some posters have erroneously claimed that a single massive pressure vessels is more efficient then many small ones, this is a common error in thinking that the pressure vessel mass scales only with surface area, in actuality it scales with volume due to a large vessel needing a thicker wall. Given the inherent danger, I would say death-trap-ishness, in a single pressure vessel the interconnecting of many individual pressure vessels is certainly the way to go.Note that a livable habitat is going to consist of a LOT more mass in equipment, life-support and otherwise beyond the pressure vessel, even a pressure vessel made 100 percent from local materials will need nearly the same amount of vital equipment to shipped in. This is the flaw in most space-cadet style housing solutions, they pretend that they are making log cabins in which just walls and roof are all that's needed and that they are saving 90 percent of the shipment mass from Earth.
A pressure envelope can be made of a thin membrane so long as it's a high tensile strength material ...
In my scenario the arcade structure provides all [the abrasion resistance and ballistic protection] allowing the actual pressure vessel to be much lighter, it is taken into the arcade and simply inflated and interconnected with other similar pressure vessels, the volume can be very large on the order of an apartment buildings each.