Pyramid Greenhouse

kbd512 · 2016-11-03 10:22:09

Josh,

Look at how much material has to be overhead to contain .5 atm on Mars. 6.8m is more than 22 feet of material that has to be overhead. Humans function best at 1 atm and that's why ISS is pressurized to 1 atm, not .5 atm. However, people can and certainly do acclimate to lower pressures over time.

Let's say the brick habitat is just a 5m square box. That means 170m^3 of material is required on all sides but the bottom to contain that pressure and uniform regolith density and regolith placement is required. In other words, the ATV has to move 850m^3 (2,788ft^3) worth of regolith. That's 6.8m x 5m x 5m (27.9ft x 16.4ft x 16.4ft).

How much power would a dozer that could move that amount of material require? Obviously it could be moved one cubic foot at a time, but how much time are you willing to spend on one 5m x 5m x 5m pressure box? How are you going to move 22ft of material up and over the top of the habitat? If you use a regolith ramp, calculate how much more regolith has to be moved. Take into account the slope or grade of the regolith ramp that a small electrical vehicle could reasonably push itself and its load of regolith up.

Here on Earth, a Bobcat can move roughly .3 cubic yards with a full load. Let's say it takes just 3 minutes to do that. 850m^3 is 1,112y^3, so that's 3707 trips and 11,121 minutes or 185 hours or 7.7 days. The Bobcat has a 50hp or 37.2kW gas engine. Here on Earth, the Bobcat weighs 2,945kg (6,480lbs). 1,200kg (456kg on Mars) is linearly scaled assumption for the weight of the machine. We do need some weight to help us drive the bucket into the regolith for collection and to keep the machine upright when carrying or pushing its load.

The tunnel boring machine I proposed for digging vertical shafts for emplacement of 5m x 10m inflatable modules only had to remove 196m^3 worth of material and it had a 400kWe fission reactor driving a 500hp electric motor to do that. It was heavy as hell, but it had a much less demanding task to accomplish with substantially more power.

Perhaps a dozen smaller robots could do what Dook wanted to do in a reasonable amount of time. There are multiple ways to solve the problem. All I know is, time is money and in the case of Mars there's a LOT of money involved.

That 7.7 days was to build a 5m x 5m x 5m box. Essentially, we built a jail cell. Now let's scale up to 10m x 10m x 5m. We're not moving 850m^3, it's now 3,400m^3.

3,400m^3 = 4,447y^3

4,447y^3 / .3y^3 = 14,823 trips

3m per trip * 14,823 = 44,470 minutes = 741hrs = 31 days

You need five machines that weigh 1,200kg each, or 6,000kg worth of machines, to complete construction within a week. For the habitat to be livable, someone has to plumb and wire each habitat created.

Can you see how this type of construction process could become prohibitively lengthy really, really fast?

It might be worth a try, just to see if quasi-Earth-like studio apartments could be built on Mars in a reasonable time frame, but here on Earth we typically use reinforced structures to provide housing using materials unavailable on Mars. The construction process also typically takes at least a week with substantial manpower and lots of liquid hydrocarbon powered machinery that we can't easily use on Mars in any practical sense.

Like I said, it's a cool concept, but do a little bit of homework to figure out what's required to go from ideation to instantiation.

Last edited by kbd512 (2016-11-03 10:25:08)

Dook · 2016-11-03 10:37:22

kbd512 wrote:

Dook wrote:
Your regolith bags are to shield the hab from radiation? Then why did you compare them to the lego wall habitat building blocks and ask why I would want to fill my launcher with them when I could just use the fabric regolith bags?
I didn't fully understand what you intended to do because I didn't fully understand what magic having 8 feet of regolith atop the habitat provided, apart from substantial radiation protection. The weight of the Martian regolith over the top of the habitat didn't correspond to anything that would provide enough counter-force to hold any breathable partial pressure atmosphere, so that was my best guess. My best guess didn't correspond with what you proposed. Mea culpa.

I didn't say putting 8 feet of regolith on top of the hab was magic. Everything the settlers do won't be "magical". It's going to take hard work. Someone already posted that the mass of the regolith on top would counteract the pressure inside a pressurized habitat. Take it up with them.

A square pressure vessel is more likely to rupture than a cylindrical one? You could build a steel box with welded seams and it will take a whole lot more pressure before it ruptures than a inflated cylindrical plastic bag.

There will likely be uneven deformation from the non-uniform regolith on top? Hehe. No, there won't. It works fine from an engineering perspective. You're rambling on and making no sense.

The Bigelow Hab is a test chamber? It is, you first.

How long do you think you're inflatable will last on Mars before it has to be replaced?

How would you obtain an even load over the top of a structure by piling up regolith using a dozer? Hehe, oh man, you're really reaching. You go by the height of the regolith, if it's higher in one section then you smooth in out. If it's lower in one area you put regolith there. I know you're going to try and argue this to death but you've obviously never seen construction before. They kind of do it all the time. It's known, just not by you.

You haven't seen too many perfectly square dirt mounds? You need to drive by a new home construction site then.

Typical housing foundations are made from concrete and foundations settle over time? Typical Earth homes are not built under ground either. On the Earth, you need to compact the soil, which means to add water and work the soil to get the air out, before building a foundation. On Mars, it would be nice to compact the regolith but that would use up all of the water but since there is no rain on Mars the regolith isn't going to go through uneven natural compaction anyway. The only changes will be temperature. The foundation will be fine.

Regolith is not the best building material but it's all over Mars? So you want a first inflatable habitat and then have the crew build other habitats made of fabric bags full of regolith?

Good luck sealing all sides of all the blocks with silicone? Heheh... I can tell you've never constructed anything before. It's actually kind of easy, you just pull the handle and the silicone comes out as you pull, hehe... There is sealant in/on your house already, sealing the window frames, under your exterior door frames, all the roof vents, high temp stuff for the heater and water heater vents.

If I can get a shoebox sized lego structure to hold 1 atmosphere I should let everyone know? Well, if I built it at sea level it would already be one atmosphere. You think that would be difficult? I wouldn't even have to seal the blocks, hehe...

Fabric and aluminum pressure vessels tend to leak in predictable places? How do you predict a tiny hole in the fabric? Aluminum? So now you want an inflated habitat and an aluminum one? You know that aluminum changes temperature quickly, right?

In a large lego structure with thousands of blocks, how would you know where to start looking? Most of the walls are pre-assembled on the earth, probably by the actual crew that is going to finish it on Mars so they can get some supervised training. But, to your point, where do they start looking for a leak? They could paint the inside of the wall with thick sealant paint like they use on the roofs of mobile homes. That's probably something they should do anyway. I'll add it to the weight list. Done.

If we can't get it to work on the Earth why use it on Mars? Uhh, did lego's just suddenly stop working on the Earth? I went to a kids birthday party not long ago and one of his toys was a lego dragon that the father put together. I think lego's are still working but if you have some kind of update that the physics of lego's has suddenly stopped working then let us know.

A cylindrical pressure vessel is better than a square pressure vessel for holding substantial pressure? To you it is, to physics it's not. The pressure will be even. Pressurized gasses don't find places to huddle together.
Kevlar is strong? Yep, it is. You can keep your idea and I can keep mine.

Dook · 2016-11-03 10:57:16

kbd512 wrote:

Dook,
Maybe it's just mis-communication, or perception on my part, but from your responses I feel as though you take some of this as some sort of personal attack. If I'm coming across that way, I apologize, as that was not the intent.
Some of the ideas you've come up with have been pretty good concepts. Going from ideation to instantiation runs smack into physics and mathematics. At that point, you have to do a bit of homework to determine just how feasible any particular idea is.
My responses to you are intended to illicit responses directed towards the feasibility of your concepts and either offer alternatives that might work or figure out how you intend to go about doing something. A lot of this is just looking up masses, dimensions, material mechanical properties, etc.
1 atm = ~14.7psi (pounds per square inch)

Is it a personalized attack? Here's what it is, you're trying to play the "I'm smarter than you are" game. People want to win. Smart people really want to win. Everyone here is smart or they wouldn't know enough about this stuff to even begin to discuss it but we all have different experiences. You guys are great with the math. I can't do it other than pretty basic stuff, but I have a lot of practical experience that you book smart guys don't have. Also, I am exceptional at efficiency while most people can't think efficiently and don't even know it.

I could never build the Athlete. I would never even begin to waste my time and money on it but NASA built it anyway. They should have known from just hearing the idea that it's never going to be used for anything.

As for the regolith vs interior pressure, I'll leave that to you and Josh. My Buried Habitat will hold the regolith on top with no interior pressure. If it didn't you couldn't even build it because the ceiling would fail as you were putting the regolith on top of it.

Dook · 2016-11-03 11:24:43

kbd512 wrote:

Josh,
Look at how much material has to be overhead to contain .5 atm on Mars. 6.8m is more than 22 feet of material that has to be overhead. Humans function best at 1 atm and that's why ISS is pressurized to 1 atm, not .5 atm. However, people can and certainly do acclimate to lower pressures over time.

The Buried Habitat is 20'x20' and 17.5' tall, and it's buried under 8 feet of regolith. Also, the pit won't be perfectly square, you have to gently slope the sides or it will cave in, and you need a long ramp to drive on. So the regolith that the two ATV's have to move would be more than you noted.

How much power would a dozer need to move all that material? There would be two ATV dozers operating at the same time. Yes, I know it's going to take some time, maybe even a month if there is permafrost that has to be constantly melted with mirrors but then if it's got ice in it then we've hit a water source.

You don't move material up and over the habitat. You make it level so you can then build a Pyramid Greenhouse over the top of it.
On the Earth, bobcats have to move wet dirt, which is heavier. On Mars, it's probably going to be as dry as dry can be and with Mars lower gravity, it's even easier.

Robots could do the work? The ATV dozers could be remotely operated from the Mars Hab. I like having an operator on board so you can get the feel of it.

A dozen robots doing it on their own? Maybe in another 100 years.

The dozer has to weigh 1,200 kg each? No, it doesn't. I have a 400 lb ATV at home with a pull behind blade on it that moves Earth dirt just fine.

You have to plumb it? You know that is just four posts and string, right?

Someone has to wire the inside? That would all be already in conduit and have a main breaker box so all the crew has to do is bolt the conduit to the walls and plug things in to the main breaker box.

Studio apartments? What?

kbd512 · 2016-11-03 13:42:53

Dook,

I guess I've never really thought about things in the context that you do. I don't post here to prove how intelligent, unintelligent, or otherwise I may be to other people I've never met and probably never will meet. I find the subject of Mars exploration fascinating and like to exchange ideas with like-minded people. Apart from whatever is going on in your head, this is not any sort of game to me, no matter what you believe about that.

I took your idea using the numbers you provided, ran with it, performed a simple sanity check, and determined that it won't work exactly the way you envisioned it. It doesn't mean that your idea can't possibly work, it just means that your idea needs to be refined into something that is workable. At the very least, that's why I thought people posted here. I also bounce ideas off of other people, see what they think, and if their thinking doesn't align with my own I ask them to indicate why so I actually learn something.

I'm human and make plenty of mistakes, too. That said, the numbers I provided are reasonably accurate rough estimates regarding the masses, dimensions, and forces involved in trying to do what you want to do.

I also outlined a very simple and inexpensive experiment that you can try yourself. If you think what you're proposing is as simple as what you imagine it to be, then make a lego box the size of a shoebox, reinforce the inside and outside with whatever types and quantities of materials you think are required to contain 14.7psi over the atmospheric pressure wherever you happen to live, and record the results. Start with a lower pressure increment, maybe 1.47psi over atmospheric, and work up from there.

The bottom line is that I said you had a good idea, I offered tweaks and alternatives that were closer to being workable and in keeping with the spirit of what I thought you intended to do (surface habitation with radiation protection, but apparently surface habitation using bricks and locally sourced materials), and apparently you thought that that was some sort of attack. If you want me to stop posting responses to you, just let me know and I'll stop responding.

kbd512 · 2016-11-03 14:12:11

Dook wrote:

The Buried Habitat is 20'x20' and 17.5' tall, and it's buried under 8 feet of regolith. Also, the pit won't be perfectly square, you have to gently slope the sides or it will cave in, and you need a long ramp to drive on. So the regolith that the two ATV's have to move would be more than you noted.

We went from burying fiberglass bricks with regolith to fabricating a steel pressure vessel on Mars, presumably welded in place which means support structure and equipment to lift the steel, and presumably the fiberglass bricks placed around the outside perimeter to add rigidity.

How much will the steel weigh (please provide the alloy you want to use and the thickness of the plates)?

How much additional volume in the lander?

Dook wrote:

How much power would a dozer need to move all that material? There would be two ATV dozers operating at the same time. Yes, I know it's going to take some time, maybe even a month if there is permafrost that has to be constantly melted with mirrors but then if it's got ice in it then we've hit a water source.

Power required would be a function of the weight of the dozer, rolling resistance, weight of the regolith to be moved (we'll simplify by using volume and bulk density), and the distance and time we're willing to devote to the task. The potentially "hard" permafrost (regolith mixed with ice) is the reason for that 1,200kg.

Dook wrote:

You don't move material up and over the habitat. You make it level so you can then build a Pyramid Greenhouse over the top of it.
On the Earth, bobcats have to move wet dirt, which is heavier. On Mars, it's probably going to be as dry as dry can be and with Mars lower gravity, it's even easier.

Ok.

Dook wrote:

Robots could do the work? The ATV dozers could be remotely operated from the Mars Hab. I like having an operator on board so you can get the feel of it.

So, optionally manned/unmanned dozer or manned dozer?

Dook wrote:

A dozen robots doing it on their own? Maybe in another 100 years.

You'd be surprised at what universities and defense contractors are up to these days, with respect to networked robotics.

Dook wrote:

The dozer has to weigh 1,200 kg each? No, it doesn't. I have a 400 lb ATV at home with a pull behind blade on it that moves Earth dirt just fine.

The mass was an estimate of a linearly scaled Bobcat. How long does it take to move a cubic meter of compact Earth with your ATV? How many hp does your ATV have? How much fuel does it use to remove a cubic meter of compacted Earth (dry and frozen)?

Dook wrote:

You have to plumb it? You know that is just four posts and string, right?

Water, Dook.

Dook wrote:

Someone has to wire the inside? That would all be already in conduit and have a main breaker box so all the crew has to do is bolt the conduit to the walls and plug things in to the main breaker box.

How much mass and volume? If a plug or something is broken or damaged, will they have spares and tools to fix it?

Dook wrote:

Studio apartments? What?

5m x 5m x 5m

Last edited by kbd512 (2016-11-03 14:12:57)

Dook · 2016-11-03 16:02:39

We went from burying fabric bricks to fabricating a steel pressure vessel on Mars? No, we didn't. You did. I never considered either an option on Mars.

Power required for the dozer is a function of blah, blah, blah? You forgot wind resistance on Tuesdays, uneven thermal expansion of the tire treads, gremlins, and a bunch of other things that only contribute to arguing for the sake of arguing.

If I have the option of a manned or unmanned dozer? I would say unmanned if they perform well enough and your dig site is within view of your Mars Hab, or the dozer has a camera system that enables you to see front and rear.

I would be surprised at what robots can do? I'm sure I would. So which one of Elon Musks missions is this robot going to be on? Which one of NASA's missions is this robot going to be on again?

How long does it take for my ATV to move a cubic meter of compact Earth? Don't know. Only designed a simple push blade for it so far, didn't design a scoop bucket. Just a quick guess, it would be 2.5' wide and have a lower lip that projects outward about 1.5' but with Mars gravity it could probably be bigger. Depending on how hard the ground is, one ATV could scrape with a blade and the other ATV would use a bucket to move it. If it's easy to move, both use buckets.

How much horsepower does the ATV have? The DC motors are 8 hp each. I have two ideas about the ATV motors, either: the ATV has two motors, one operates both front wheels, the other operates both rear wheels, or, the ATV has three motors, one for each rear wheel and one that operates both front wheels. There would be switches to use 1, 2, or 3 motors. If you had to go somewhere far you could use 1 wheel drive and just go but 2 wheel drive, and maybe four wheel drive, will be needed for moving regolith.

Someone has to plumb the hab with water? No, they don't. The bathroom has a plastic shower that has a DC pump that pumps recylced/filtered water over and over. The toilet is for catching solid waste into mylar bags that have tiny vent holes so you can microwave the water out. The urine in the urinal is filtered and used in the shower. The water tank supplying the shower would need to be emptied at times so you would take water out in a recycled water bucket and use it to water the plants. The bedrooms don't have their own water. The kitchen would have a clear plastic jug on the countertop that you walk over to and push the botton to get water.

What's the mass and volume of the wiring for the habitat? Don't know, not much. The only thing you have to wire is the LED lights and the shower DC pump. Other things can be next to the breaker panel like the heating fan, the CO2 scrubber, and the oxygen sensing system.

Will they have spares? If a plug is broken then you wire it directly to the outlet. How come academics don't know how to solve even the simplest problems without trying to make it a thousand times more complicated than it really is?

kbd512 · 2016-11-03 17:18:42

Dook wrote:

We went from burying fabric bricks to fabricating a steel pressure vessel on Mars? No, we didn't. You did. I never considered either an option on Mars.

You didn't?

Dook wrote:

A square pressure vessel is more likely to rupture than a cylindrical one? You could build a steel box with welded seams and it will take a whole lot more pressure before it ruptures than a inflated cylindrical plastic bag.

What's that?

What could all those engineers who designed cylindrical modules for the space station possibly be thinking?

We need square rockets, too. We'll just weld the seams of conex boxes together, put some dynamite in the back, and show them fellers at NASA how it's done.

Dook wrote:

Power required for the dozer is a function of blah, blah, blah?

Power - blah
Weight - blah
Volume - blah

We're having a crackin good "blah" here, or an argument, as you call it.

After our first few exchanges, and the exchanges I've read between you and other members here, it's pretty clear that we came here for different reasons. Over here, when you post something, someone might actually expect that there is some small chance that whatever you proposed might actually work. They may even ask you questions about your proposal or submit counter-proposals. Your ego seems a bit too invested into your ideas to consider alternatives and you're a little short on rational explanations or simple math backing your assertions.

I've heard enough of the same thing. I'll post elsewhere. Enjoy your echo chamber.

JoshNH4H · 2016-11-04 22:35:49

I don't want to jump into the fray here except to give a couple numbers. I don't believe it's a good idea to use loose regolith as a structural element for horizontal forces because then you're depending on its structural integrity, which you already know to be lacking.

I believe that you still need to contain pressure along two axes and therefore need a rounded exterior (although if you do the buildings the way I want to do them, they will be rounded top to bottom rather than around which would enable square buildings!).

Dook, a cube is the wrong shape to use to hold in pressure. The reason why is that the force acts in such a way as to generate a torque around the points where it's bonded to other material. It bows out, bends, deforms, or breaks. There is a mathematically correct shape to hold in pressure, and that's a sphere. In general, the closer a shape is to a sphere the better suited it is to holding in pressure. In spherical and rounded shapes, the material is entirely in tension, which spreads the load as evenly as possible around the surface.

Lego bricks are also a poor choice for wall construction, and here's why: Bricks as you've described them by the nature of their shape are not good at conducting force. What I mean by that is that your brick wall is going to have to hold in a lot of force. Because it has to be round it will be in tension. Because force is transmitted at the numbs (Shall we call them the "male end"?) of the lego, all of the force is concentrated in the cross sections of those male ends. Instead of transmitting forces through the entire brick, then, there's a small section of it that needs to carry the force. (This force is called a "shear" force, which is the complement to tensile and compressive forces. Most materials are approximately 30% weaker in shear than they are in tension or compression).

There's a certain extent to which you're right about inflatables, insofar as they can get holes poked in them. But it's pretty easy to design around them. When someone says "inflatable space habitat", you shouldn't think of a balloon or a plastic bag. You probably shouldn't even think of an air mattress. You should be thinking more like heavy fabrics with sealants, multilayered and thick. You're not the first to think about the possibility of an inflatable popping, but it is a problem they're very aware of and plan to prevent.

I believe that we have every reason to believe that a 50 kPa (0.5 atm) hab environment would be entirely breathable, comfortable, and healthy.

I believe we can easily do experiments with this now (and develop better life support in the process?) and figure this out approximately now.

Anyway, 0.5 atm at 2 kg/L on Mars is 6.8 m, or 22 feet. It's a mass of 13.5 tonnes per square meter. For a 25 square meter hab, it's a volume of 170 cubic meters. But you can get twice the space with two floors.

Technically, you don't need to be able to support the entire weight of the roof. If you pressurize a bit and then put fill on the roof a bit, you can do it in stages, but it's a lot more risky.

SpaceNut · 2016-11-05 08:25:05

Counter pressure to internal pressure for a Equilibrium valure of a net zero on the wall in wich the forces are not just vertical.

ya its a star but its the same principle
http://www.astronomy.ohio-state.edu/~po … cture.html

Hydrostatic Equilibrium
Two opposing forces are at work within a star:
Gravity pulling inward wants to make the star contract.
Pressure pushing outwards wants to make star star expand.
Pressure & Gravity work on each other:
Gravity confines the gas in the star against Pressure expansion.
Pressure supports the star against Gravitational collapse.

So we are talking about Stability Of Structures: Basic Concepts

With a tank we are calling it a pressure vessel where the structural wall thickness and strength hold the gas in from escape. https://en.wikipedia.org/wiki/Internal_pressure

Thin Walled Pressure Vessels

Dook · 2016-11-05 11:47:59

JoshNH4H wrote:

I don't want to jump into the fray here except to give a couple numbers. I don't believe it's a good idea to use loose regolith as a structural element for horizontal forces because then you're depending on its structural integrity, which you already know to be lacking.
I believe that you still need to contain pressure along two axes and therefore need a rounded exterior (although if you do the buildings the way I want to do them, they will be rounded top to bottom rather than around which would enable square buildings!).
Dook, a cube is the wrong shape to use to hold in pressure. The reason why is that the force acts in such a way as to generate a torque around the points where it's bonded to other material. It bows out, bends, deforms, or breaks. There is a mathematically correct shape to hold in pressure, and that's a sphere. In general, the closer a shape is to a sphere the better suited it is to holding in pressure. In spherical and rounded shapes, the material is entirely in tension, which spreads the load as evenly as possible around the surface.
Lego bricks are also a poor choice for wall construction, and here's why: Bricks as you've described them by the nature of their shape are not good at conducting force. What I mean by that is that your brick wall is going to have to hold in a lot of force. Because it has to be round it will be in tension. Because force is transmitted at the numbs (Shall we call them the "male end"?) of the lego, all of the force is concentrated in the cross sections of those male ends. Instead of transmitting forces through the entire brick, then, there's a small section of it that needs to carry the force. (This force is called a "shear" force, which is the complement to tensile and compressive forces. Most materials are approximately 30% weaker in shear than they are in tension or compression).
There's a certain extent to which you're right about inflatables, insofar as they can get holes poked in them. But it's pretty easy to design around them. When someone says "inflatable space habitat", you shouldn't think of a balloon or a plastic bag. You probably shouldn't even think of an air mattress. You should be thinking more like heavy fabrics with sealants, multilayered and thick. You're not the first to think about the possibility of an inflatable popping, but it is a problem they're very aware of and plan to prevent.
I believe that we have every reason to believe that a 50 kPa (0.5 atm) hab environment would be entirely breathable, comfortable, and healthy.
I believe we can easily do experiments with this now (and develop better life support in the process?) and figure this out approximately now.
Anyway, 0.5 atm at 2 kg/L on Mars is 6.8 m, or 22 feet. It's a mass of 13.5 tonnes per square meter. For a 25 square meter hab, it's a volume of 170 cubic meters. But you can get twice the space with two floors.
Technically, you don't need to be able to support the entire weight of the roof. If you pressurize a bit and then put fill on the roof a bit, you can do it in stages, but it's a lot more risky.

A cube is a more normal living space for humans. I didn't really think of it but we could build a cylindrical space with the walls being made of the same lego blocks, each wall block would just be curved slightly and the floor and ceiling panels would be circles.

Internal pressure works equally on all sides of a pressurized container. The pressure doesn't know where the container is weakest. The square container would only deform if it wasn't strong enough to contain the pressure and the walls will have regolith on their outside and the ceiling will have regolith on top of it. We're talking about, what, 7 lbs of internal pressure per square inch. I know it works out to be a lot for a large space but if an inflatable can hold it then why can't structural blocks and panels?

Lego style blocks are not good at conducting force because only the male numbs will carry the force? Pressurized fluid works on all sides equally and the numbs are thick fiberglass, each one is probably 1" and there are six on top of each block.

I shouldn't think of inflatables as thin plastic? The greenhouses will be thin plastic. That's all of your food protected by thin plastic.

The living inflatables will be heavy fabric? It's fabric. What happens when a thread breaks? The inflatable will form a bubble. Your inflatable is the one that is more likely to bow, bend, or break. How much pressure does it take to deform 1/4" thick fiberglass?

They are prepared to handle it if it distorts? Yeah, they run, if they have time. If it fails quickly the habitat collapses on top of them. And then, how do they fix it?

My structural blocks will have counterbalanced force acting on all sides. Your inflatable is on it's own.

What is the lifespan of one of these inflatables? I keep asking and no one seems to know. You don't think it's 100 years, do you? For the thin plastic greenhouse ones I'd say it might be 1-2 years. So, we need to resupply the base with them. For the fabric inflatable, I don't know, 5 years?

You trust thin plastic and thin fabric but not thick fiberglass with multiple layers?

GW Johnson · 2016-11-05 12:47:42

Well, the Apollo LM held ~5 psi O2 with about .020 inch thick aluminum sheet metal. That's something you can poke a pencil through. Rather easily. Wouldn't be my choice for a domicile anywhere, actually.

And then there's Bigelow's inflatables, which are many different layers and about half a meter thick. And it's rated as a micrometeor shield. There's a small one docked at ISS now. Bigelow wants to build his own private station with bigger ones known as B-330's. This stuff is NOT transparent. Bigelow builds windows into his B-330's, but only a couple of them.

As for fiberglass panels, I've never seen anything offered commercially more than 3/16 inch thick. Most is well under 1/8. Won't stop hail. Boat hulls, unless for very large craft, are usually in that same thickness range. Some of them are quite tough. The best I ever built was two layers of woven roven on top of two layers of fine boat cloth. They are not all that transparent.

It was good for the rocks in river-running as a 16 foot canoe weighing 65 pounds. Easy to patch, both temporarily and permanently, and cracks generally did not propagate. You get the strength/weight by not drowning the cloth with resin, just barely wet it. The gel (color) coat seals the porosity so it doesn't leak.

If you use kevlar fabrics instead of glass, and a compatible resin (usually epoxy), you can get double the fracture and puncture toughness for the same weight, at the cost of lower stiffness and more $. That's been a common aircraft interior panel material since the early 1960's. Women's spike heels would puncture the original aluminum decking when the jet airliners first came out.

One thing to consider is what atmosphere you may require for long term exposures, especially pregnant women. We evolved at 0.5 to 1.0 atm 21% (vol) O2. That's the sure thing. The 0.5 atmosphere corresponds to those folks who live in the mountains at 15-18,000 feet. You have to acclimatize to that, and it takes a long time, but it's been done for millennia.

Anybody can quickly acclimatize to 5-10,000 feet, which is 68-83% of an atmosphere. Just something to think about. But it says synthetic air at about 10 psia ought to be OK. For just about anybody. And just about any purpose.

GW

Dook · 2016-11-05 13:17:47

You know, making the buried habitat a cylinder instead of a square shape solves some problems. I can use floor panels that are one piece instead of four panels put together. Zubrin's tuna can is 33' in diameter so I think the floor and ceiling panels can be 31' in diameter.

Also, since you don't have to deal with corners you no longer have to keep each of the lego blocks twice as long as their width so they can be long curved rectangular blocks. Most of the wall sections would already be pre-assembled but the rest of the assembly would go much quicker.

One drawback might be that moving the large circular floor and ceiling panels would require all three settlers though and you would never want to have all three in the rover at the same time to go out and move the panels onto the Mars Cart. You want one back at the base who can come and get you if you break down or get stuck. The panels would have to be extremely light but their size alone would be tough for two to move. I have to think about that one. The solution might just be to make the circle panels a bit smaller.

Dook · 2016-11-05 13:32:16

GW Johnson wrote:

Well, the Apollo LM held ~5 psi O2 with about .020 inch thick aluminum sheet metal. That's something you can poke a pencil through. Rather easily. Wouldn't be my choice for a domicile anywhere, actually.
And then there's Bigelow's inflatables, which are many different layers and about half a meter thick. And it's rated as a micrometeor shield. There's a small one docked at ISS now. Bigelow wants to build his own private station with bigger ones known as B-330's. This stuff is NOT transparent. Bigelow builds windows into his B-330's, but only a couple of them.
As for fiberglass panels, I've never seen anything offered commercially more than 3/16 inch thick. Most is well under 1/8. Won't stop hail. Boat hulls, unless for very large craft, are usually in that same thickness range. Some of them are quite tough. The best I ever built was two layers of woven roven on top of two layers of fine boat cloth. They are not all that transparent.
It was good for the rocks in river-running as a 16 foot canoe weighing 65 pounds. Easy to patch, both temporarily and permanently, and cracks generally did not propagate. You get the strength/weight by not drowning the cloth with resin, just barely wet it. The gel (color) coat seals the porosity so it doesn't leak.
If you use kevlar fabrics instead of glass, and a compatible resin (usually epoxy), you can get double the fracture and puncture toughness for the same weight, at the cost of lower stiffness and more $. That's been a common aircraft interior panel material since the early 1960's. Women's spike heels would puncture the original aluminum decking when the jet airliners first came out.
One thing to consider is what atmosphere you may require for long term exposures, especially pregnant women. We evolved at 0.5 to 1.0 atm 21% (vol) O2. That's the sure thing. The 0.5 atmosphere corresponds to those folks who live in the mountains at 15-18,000 feet. You have to acclimatize to that, and it takes a long time, but it's been done for millennia.
Anybody can quickly acclimatize to 5-10,000 feet, which is 68-83% of an atmosphere. Just something to think about. But it says synthetic air at about 10 psia ought to be OK. For just about anybody. And just about any purpose.
GW

You can make fiberglass any thickness you want, just add more layers of matting. The lego blocks would be 1/4" thick and molded into a lego block shape.

The flooring and ceiling panels are a composite of fiberglass panels and honeycomb that is 6" thick. They would be very strong and relatively light compared to other sturdy building materials. The lego wall blocks are like bricks but they lock into each other. They are strong if kept in compression. If you tried to build a surface habitat out of them, with no regolith on top, once you pressurized it they would blow apart.

Kevlar would greatly increase the strength of the panels and blocks but I think that's overkill.

Last edited by Dook (2016-11-05 13:34:23)

GW Johnson · 2016-11-05 13:35:25

Don't use fiberglass matting. Use the woven-roven cloth, it's plenty coarse. Matting sops up lots of resin and adds weight, but little or no strength. Worthless as a structural material. I see no purpose to thickness that is just plain weak.

GW

JoshNH4H · 2016-11-05 15:27:02

Dook,

I have already explained to you why a square pressure vessel is an incorrect shape. If you didn't understand, I would be glad to explain it again in a different way.

I have also explained why lego bricks are a poor way to construct a pressure vessel. If you didn't understand, I would be glad to explain it again in a different way.

If you are instead going to ignore these explanations and continue being wrong, that is your right. I do not plan to engage with you as long as you ignore the well-established engineering principles after having been made aware of them.

Dook · 2016-11-05 16:23:35

JoshNH4H wrote:

Dook,
I have already explained to you why a square pressure vessel is an incorrect shape. If you didn't understand, I would be glad to explain it again in a different way.
I have also explained why lego bricks are a poor way to construct a pressure vessel. If you didn't understand, I would be glad to explain it again in a different way.
If you are instead going to ignore these explanations and continue being wrong, that is your right. I do not plan to engage with you as long as you ignore the well-established engineering principles after having been made aware of them.

Okay, I know what you are trying to say. A spherical pressure vessel of the same thickness will be stronger than a cylinder shaped pressure vessel and cylinders are stronger than square shapes. But if we use that logic, steel is stronger than fabric, therefore the habitat on Mars should be made of a spherical steel ball? That would be ridiculous, right?

We're not building something that can hold in as much pressure as possible. Making the habitat so strong that it can hold in 3,000 psi doesn't give us any benefit. It only needs to hold in, what, 7 psi?

I know you guys are really into inflatables. What is the life expectancy of an inflatable hab on Mars? Someone pick a number.

SpaceNut · 2016-11-05 20:48:13

One problem that I can think of is when the internal pressure drops and replentishes is that there will be chafing on the outer surface against the regolith that we would pile on top of it. Over time and numerous cycles this could lead to failure of the inflatable.

Dook · 2016-11-05 21:03:32

You want to bury an inflatable? I never understand people.

There are some things you can cut back on to save weight and cost, every meal doesn't have to be steak and lobster, they don't need a movie theater on Mars, but having a sturdy long lasting shelter is not something you try to cut back on. It has to last.

SpaceNut · 2016-11-05 21:13:14

Actually no Dook that is why I meantion the one problem that I could fore see from using it in that manner...

Terraformer · 2016-11-06 10:04:34

I know you guys are really into inflatables. What is the life expectancy of an inflatable hab on Mars? Someone pick a number.

Only if you give parameters. Are we talking about a thin plastic bag, or multiple levels of kevlar? What is it made of? Is it exposed straight to the environment, or enclosed by regolith walls to provide protection from the external environment so that it only has to hold in the pressure?

Dook · 2016-11-06 11:29:02

Terraformer wrote:

I know you guys are really into inflatables. What is the life expectancy of an inflatable hab on Mars? Someone pick a number.
Only if you give parameters. Are we talking about a thin plastic bag, or multiple levels of kevlar? What is it made of? Is it exposed straight to the environment, or enclosed by regolith walls to provide protection from the external environment so that it only has to hold in the pressure?

You can't just give some numbers for both?

How about a thin plastic greenhouse built on the surface of Mars at noon on a Tuesday. And then a Bigelow inflatable inflated on the surface of Mars with no regolith on top of it or on it's sides, and it is finished on a Friday.

The thing is that there's just no way for you to know how long a thin plastic greenhouse or a fabric habitat will last on Mars. And that's a problem, a big one.

A buried habitat and a greenhouse built with strong components should last 200 years, or more.

You have to prioritize better. Some things matter more than others. The habitat and greenhouses have to last as long as possible and you can fit BOTH in one Mars Direct launch so why not upgrade the components?

You're trying to cut the weight of critical items so you can take more people because you have a self imposed sense of urgency.

SpaceNut · 2016-11-06 18:34:17

Current in space relative to temperature cycles per orbital time are the July 12, 2006, and June 28, 2007, Bigelow launched the Genesis I and II modules, each (11.5 m3 (410 cu ft)) respectively, which while the power systems are no longer active are still on orbit and inflated. The orbital life of Genesis II is estimated to be 12 years give or take, with a gradually decaying orbit resulting in re-entry into Earth's atmosphere and burn-up expected.

https://en.wikipedia.org/wiki/Bigelow_Aerospace

I think the condition on orbit are harsher than what mars will see but I might be wrong....

JoshNH4H · 2016-11-14 09:37:22

Hey Dook,

Sorry for not replying sooner, but I've spent much of the past week working on my Chemical Rockets post in the Aluminium Smelting thread. By the way, I'd encourage you all to check that out if you haven't already.

Back on topic:

Dook wrote:

Okay, I know what you are trying to say. A spherical pressure vessel of the same thickness will be stronger than a cylinder shaped pressure vessel and cylinders are stronger than square shapes. But if we use that logic, steel is stronger than fabric, therefore the habitat on Mars should be made of a spherical steel ball? That would be ridiculous, right?
We're not building something that can hold in as much pressure as possible. Making the habitat so strong that it can hold in 3,000 psi doesn't give us any benefit. It only needs to hold in, what, 7 psi?

Now we're speaking the same language! Glad to see it. You're absolutely right that a myopic focus on minimizing the mass of the habitat is the wrong way to go. Taken to an absolute extreme, by cancelling the mission you can reduce your mass to Mars to zero. Now there's some cost savings!

More seriously, there are other considerations besides cost. A cylinder is a more useful shape than a sphere. To be clear, when we say "cylinder", we mean a capped cylinder. There's a bit of math behind this.

Basically, the amount of tension on the curved outside of a pressure vessel is proportional to the inverse of the radius of curvature. In other words, the closer a section is to straight, the lower the tensile forces on it will be. For example, if you have an egg-shaped pressure vessel, the flatter bottom part would be under less stress than the smaller, rounder top part.

Now consider a cube. Cubes have hard, 90 degree corners. The radius of curvature of a hard corner is zero, so according to this model the stress is infinite. What happens in the real world is that the sides of the cube would bow out--often quite a lot--and either burst or deform until some larger radius of curvature has been reached. While this is absolutely a matter of cost-benefit, the cost to having a cubical habitat is that it needs to be much, much, much stronger to contain an equivalent pressure.

I'm open to the idea that some things are worth the extra weight, but as far as pressure vessels go there's no conceivable reason why you would choose a cubic shape when other shapes are available.

By the way, fibers can be quite strong. Kevlar is way stronger than steel, and so is carbon fiber.

The rule of thumb for me is that you don't save any weight with an inflatable, but you do save on space. Given that there will be limits to the size of your launch vehicle and your entry vehicle, saving space is often a necessity.

Dook wrote:

I know you guys are really into inflatables. What is the life expectancy of an inflatable hab on Mars? Someone pick a number.

I'll probably regret giving you a number, but let's say 5-10 years for a durable inflatable.

SpaceNut · 2016-11-14 22:29:19

So if we are making the shell from insitu materials then the Composite Pressure vessel

here is how we can go about making it Simple methods for molding fiberglass and carbon fiber

I believe basalt fibers are possible are there others?

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