Okay, but how are you going to get all that sand and rock to stick to your dome without having to move a mountain of material?
Regarding the sand and rock reducing the weight of the gas envelope, I'd think that the added weight of the sand and rock would be yet another load that your envelope would have to be strengthened against.
I understand that sand and rock can shield you against radiation, but how thick a layer would you need to cover up with in order to guard against a meteor strike, especially if it's loose sand and rock?
It just sounds like this structure would not be a rigid shell. In which case, why not minimize the mechanical loads on it, and just use it for simple greenhouse purposes?
Why would you protect from meteorites?
The Mars atmosphere will adequately shield from micrometeorites. And you don't shield from meteorites on earth. It's just one of those risks.
A dome might be built like the ancient builders of cathedrals did. Form a dome of sand and lay formed blocks of stone or concrete over it. The completed dome will be strong enough for a big load even if unpressurized. Then roemove the sand from inside and pile enough dirt over it to withstand the airpressure when the structure is pressurized. That's probably 10m or more as even a cast iron dome would need to be several meters thick or it is lifted from its foundation by air pressure.
I think that's a bit like arguing that sticking an inner tube inside a tire will result in the need for a heavier inner tube to resist the pressure exerted on it by the tire.
QuoteIt just sounds like this structure would not be a rigid shell. In which case, why not minimize the mechanical loads on it, and just use it for simple greenhouse purposes?See title of thread.
Quote from: guckyfan on 07/13/2013 03:16 amWhy would you protect from meteorites?Because they could puncture your dome, which could be fatal to the inhabitants.QuoteThe Mars atmosphere will adequately shield from micrometeorites. And you don't shield from meteorites on earth. It's just one of those risks.But on Earth there's no real risk of asphyxiating if a meteor punches a whole in your roof.
But how airtight would this solution likely be?
By the same token you could inflate a dome or form, and pour cement directly over it to make a shell that way.Anyway, consider that an unshielded dome could be a quick way to do large-scale crop cultivation, to scale up food output on Mars. It would require less work to erect and would be less safe, but crops don't warrant the same safeguards that people do. You could also have livestock in there, to supply meat and dairy.
Quote from: Andrew_W on 07/13/2013 03:32 amI think that's a bit like arguing that sticking an inner tube inside a tire will result in the need for a heavier inner tube to resist the pressure exerted on it by the tire.Not sure I agree - the inner tube is meant to oppose the compressive load of the vehicle, relative to which the tire's compressive load is minimal.A Mars dome would be experiencing a decompression load from the atmosphere within. If you put your rocks on top to oppose this then you have a compressive load from above, but this load won't be homogenous and symmetric like a fluid. There's going to be unevenness that puts a further strain on your envelope, instead of perfectly balancing the air pressure.QuoteQuoteIt just sounds like this structure would not be a rigid shell. In which case, why not minimize the mechanical loads on it, and just use it for simple greenhouse purposes?See title of thread.Well, greenhouses or crop fields are living spaces too - just not for people primarily - and they can provide a valuable resource buffer to a colony, by scaling up food cultivation. Could be a lot cheaper on scalability than growing everything hydroponically.
How's this for an alternative:1. Find a suitable crater in a suitable location - easier than locating a suitable cave in a suitable location.2. Inflate, to low pressure, a gas proof liner in the bottom of it.3. Throw fine sand (screened to remove larger rocks) over the liner.4. once the liner is adequately protected by sand you can start chucking in larger rocks.5. Slowly increase the pressure to match the increasing weight on the liner.6. move in furniture.
I'm not fond of non rigid structures balancing air pressure within and weight of soil above. One effect you'll get is a runaway instability where a small deficit in mass over one spot will cause that part of the liner to rise, as it does the soil above gradually displaces, and you basically get a bubble blow out.
Oh and btw, regarding rigid natural structures or man made cavities. You don't have to apply rigid gas tight membranes or pre-make them to form. A better way is to spray on a material. Given you only need a thin membrane there's an argument for importing the material. A suitable material would be ordinary polyethylene. Just heat and spray.
I really do not understand how the idea to use water in building on Mars. I don't see using a material that is liquid in the temperaturerange suitable for humans for building human habitats.YMMV though.
Or the answer to the "Fastest Way to Expand Living Space on Mars" could be terraforming Mars. If you thought a project of global terraforming was workable- which I don't. I think we will terraform Mars in sense that human have been terraforming earth for thousands of years or perhaps more significantly within the last century or two. Or life [rather than human] has been terraforming Earth for billions of years.