Optimal size for domes and other structures

[tater]

There was talk of waterless "concrete" using sulfur as well, I recall.

[Nuke]

lunacrete has made its rounds before. i mean you can do wonders with shotcrete and rebar. assuming you can make rebar. and shotcrete, and have one of those big concrete pump rigs. i suppose you could do it with forms and a shovel though. having done that kind of work before, idk if id want to do it while also wearing a space suit.

Edited January 4 by Nuke

[darthgently]

20 minutes ago, Nuke said:

lunacrete has made its rounds before. i mean you can do wonders with shotcrete and rebar. assuming you can make rebar. and shotcrete, and have one of those big concrete pump rigs. i suppose you could do it with forms and a shovel though. having done that kind of work before, idk if id want to do it while also wearing a space suit.

That is where your space suit has the crew chief patches and the robots have the deck hand insignia.

Remember to always lift properly!  Lift with your deck hands!

[StrandedonEarth]

2 hours ago, StrandedonEarth said:

What if they used butyl rubber, which is used for the airtight liner in tires?

This is what I get for posting while waking up. Rubber needs to be cured with temperature and pressure.  Although the silly concept of a “bomb cure” occurs to me: spray the butyl liner, close the doors,  pump in a calculated and measured explosive mix of gasses, and detonate, filling the chamber with hot, high-pressure gas. As a bonus, this will test the structural integrity of the chamber. 
 

Yeah, I know, crazy idea…

Spoiler

 

Edited January 4 by StrandedonEarth

[tater]

Hear me out:

Project Gnome, SE NM (3.5 kT device, underground)

[Nuke]

yet another problem that can be solved with nuclear weapons.

[Pthigrivi]

14 hours ago, tater said:

BTW, @Pthigrivi, these designs (and underlying observations about concerns/requirements/etc) are extremely interesting stuff.

Thanks, dude  Its been a fun little after-dinner thought experiment. I might move into 3d after Im more confident I’ve got base assumptions right. 
 

My new problem is Ive been WAY underestimating air pressure. You can’t have workers decompressing and recompressing all the time so basically every habitable space needs to be at 14.3psi. Thats actually plenty to carry 3m of regolith. Id been thinking it wasn’t safe to have the internal pressure do the structural lifting but if you have a catastrophic pressure failure you’ve got worse problems than the roof caving in. The new plan is to make tubular aluminum pressure vessels, (always need 2 means of emergency egress) pressurize them, then bury them in regolith. 

You can start by shipping something like this from earth, inflating it, burying it, and using it as a workspace for building hab vessels nearly as big inside. 

 

Edited January 4 by Pthigrivi

[AckSed]

I have to say thank you as well, it's been fascinating to see an architect go at habitat design.

I might not always agree with it, but it's exploring the problem-space in a new way.

[StrandedonEarth]

19 minutes ago, Pthigrivi said:

My new problem is Ive been WAY underestimating air pressure. You can’t have workers decompressing and recompressing all the time so basically every habitable space needs to be at 14.3psi. Thats actually plenty to carry 3m of regolith. Id been thinking it wasn’t safe to have the internal pressure do the structural lifting but if you have a catastrophic pressure failure you’ve got worse problems than the roof caving in.

Hmmm. The neat thing about supporting the ‘lith cover with air pressure is that if there is a leak, or the airlocks need to be cycled rapidly, the pressure would remain nearly constant as the roof sags. The downside is that leaks wouldn’t naturally slow due to lessening of the pressure differential. 

[Entropian]

8 hours ago, StrandedonEarth said:

What if they used butyl rubber, which is used for the airtight liner in tires?

I believe butyl is used in KF joints as an O-ring polymer, so it'll be a damn sight better than vinyl.  Aside from something like Viton, butyl should be in the upper tier of polymers you'd want to use.

7 hours ago, farmerben said:

I'm afraid you will require a small maintenance replacement air program no matter what.  If you lose half your air to airlocks and active operations, and half your air to painted rocks that enclose a huge amount of space it would be worth it.  The air flow rate through solid basalt is not very great to begin with.

An air maintenance program is a necessity, but that doesn't mean you can just wave away any air loss mechanism with it.  Vinyl in particular is a serious offender when it comes to outgassing, and you'd want to avoid it at nearly all costs.  Sure, it's pretty easy to apply, but I'm sure the smart dudes at NASA or some other group would be able to come up with a method for a lower-outgassing polymer.  The paint-based idea is much closer to what I had in mind.  One can just spray a substrate on the walls, then cover it with a stronger sealant, like some kind of epoxy perhaps.  In my experience, epoxy cured under vacuum has pretty low outgassing at least.

Edited January 4 by Entropian

[Pthigrivi]

3 hours ago, StrandedonEarth said:

Hmmm. The neat thing about supporting the ‘lith cover with air pressure is that if there is a leak, or the airlocks need to be cycled rapidly, the pressure would remain nearly constant as the roof sags. The downside is that leaks wouldn’t naturally slow due to lessening of the pressure differential. 

This is where Im a bit back and forth. A small leak isn’t going to cause huge problems and should be detectable and easily compensated for until it could be repaired. Fire is a bigger risk.  You’d need more robust protections in industrial environments but even in regular habs youre going to have occasional cooking, electrical, and battery fires. Thats why egress is so important, and you’d definitely also want redundant sprinkler systems. With proper safety protocols the only thing I can think of that would be a real threat is someone deliberately blowing a meters wide hole in the envelope. I mean with thousands or millions of people you’re gonna get some nuts. That would be incredibly dangerous but my previous designs are also vulnerable to bombings. Best you can do is very tightly control access to explosives (for industrial blasting for instance) and compartmentalize each hab so a compromised module could be evacuated (if possible) and then sealed off. 

Edited January 4 by Pthigrivi

[farmerben]

4 hours ago, Pthigrivi said:

 

My new problem is Ive been WAY underestimating air pressure. You can’t have workers decompressing and recompressing all the time so basically every habitable space needs to be at 14.3psi. 

 

 

Hmmm.  They might decide to keep their habitats at 1/2 an atm.  That would be like living in Machu Pichu, humans can adapt to it.

[Pthigrivi]

1 hour ago, farmerben said:

Hmmm.  They might decide to keep their habitats at 1/2 an atm.  That would be like living in Machu Pichu, humans can adapt to it.

I was thinking about this earlier. Ive been to Cuzco and Badrinath India and its a doozy but you can adjust. Maybe even tweak the oxygen mix to make things easier. Since Im no longer relying on a concrete structure basically all of my radiation mass is coming from regolith.  3m translates to about 600 g/cm^2. Air pressure in Cuzco is about 10psi or 700 g/cm^2. It works, it makes a lot of other things easier, but since Im doing this crazy thing using pressure to reinforce structure I just hedged by keeping things at 14.3psi (1000 g/cm^2) for safety margin. But maybe Im fine because gravity is 38%? 
 

I love this because it strains my intuitions and mathing capacity. I mean we used to drop our tire pressure down to 15psi to dive on the beach because it made them spongy and get more traction. But now Im holding up 10ft of soil with that? If I poke a 1m hole in a tube thats 16m in diameter and 100m long how quickly  will the air rush out? What about 3m hole? Ive already got my HVAC mains sized to 2m. Maybe after a rapid pressure loss you could drive all of that into the compromised compartment until it could be evacuated?

Edited January 5 by Pthigrivi

[darthgently]

In case of breach we’d need as a backup inflatable body bags with attached PLSS that ppl could zip up in quick (bots could do this if unconscious or injured) and robots could carry them to safety in some still  pressurized area.

A little macabre looking, but you’ll live!

[Pthigrivi]

20 minutes ago, darthgently said:

In case of breach we’d need as a backup inflatable body bags with attached PLSS that ppl could zip up in quick (bots could do this if unconscious or injured) and robots could carry them to safety in some still  pressurized area.

A little macabre looking, but you’ll live!

Look probably (hopefully?) the risk of terrorism is low but yknow you may or may not have signed a bunch of papers hoping for adventure and a new life only to have your passport confiscated and find yourself on another planet condemned to live in an oppressive company town where you’re working 16h days terminally in debt with no constitutional rights and you cant even go outside because its -100f with no breathable atmosphere. Maybe not everyone loses it but like fast-react safe rooms aren’t necessarily a bad idea. 

[darthgently]

11 minutes ago, Pthigrivi said:

Look probably (hopefully?) the risk of terrorism is low but yknow you may or may not have signed a bunch of papers hoping for adventure and a new life only to have your passport confiscated and find yourself on another planet condemned to live in an oppressive company town where you’re working 16h days terminally in debt with no constitutional rights and you cant even go outside because its -100f with no breathable atmosphere. Maybe not everyone loses it but like fast-react safe rooms aren’t necessarily a bad idea. 

I was thinking meteor or simply an engineering miscalc leading to a pressure breach, but sure, could be an Expanse Belter scenario or Space Extinctionists trying to suicide the base I suppose.

[Pthigrivi]

I think these are getting better and better each pass. The enclosure now is 3m of regolith, aluminum pressure vessel, 50cm of rockwool insulation, and an electric radiant inner wall panel w/ vapor barrier. The interior structure can all be steel with replaceable enamel panels and rockwool sound deadening. Given the intensely enclosed space I'd like to reduce VOCs as much as possible. At 3 stories deep Im looking at a population density of about 150 people/acre including hydroponics. Thats about 10.5 square miles for a million people. I haven't gotten back to major public spaces but Im liking the idea of mall-like multistory canyons with shops + restaurants opening onto each level, reflected light coming in through the ceiling and views of the horizon from the upper boulevards. 



Edit: Something like this? Bigger? I should go  bigger.


 

Edited January 7 by Pthigrivi

[tater]

2 hours ago, Pthigrivi said:

Edit: Something like this? Bigger? I should go  bigger.

ASCE has conferences where this sort of work can be presented... noodle around in this thread long enough, get a paper out of it

 

[darthgently]

Some pondering this morning.  The liquid water reservoirs on Mars discovered from seismic data range from 11.5 to 20km from the surface.  The temperatures in this range could be from 0C to 30C with depth.

If a tunnel boring machine were to bore on an initial 3 degree slope downward from a 365km distance from a 20km deep reservoir all the way to that reservoir it would provide access to water, areothermal heat, and side tunnels and chambers along its length could provide vast amounts of pressurized space.

Conservative estimates of Prufrock 4 boring speed is 1 mile, or 1.6 km, per week.  So this main tunnel could be bored in under 4-1/2 earth years.

A drop in the bucket on the scales we usually talk about.  About 2 transfer windows.

If one doesn’t mind a steeper grade in the main tunnel it could be significantly less time.  But I think keeping it under say 10 degree slope at entrance would be more livable and less dangerous.  It should be safely navigable in less than ideal conditions and conducive to TBM operation.

At a 10 degree entrance slope a straight tunnel to a 20km depth would take 1.5 earth years to cut.

Interestingly, the 3 degree entrance slope in a straight tunnel on Mars becomes zero slope at 20km below the surface as this tunnel would be the midpoint of a chord connecting two surface points.  So the tunnel would be level in the liquid water, summer day temperature zone.  Yes, I worked backward from there to get the 3 degree slope entrance.

 I’m thinking run the tunnel adjacent just above and off to the side of the reservoir then slant drill on another gentle slope down to the water.