I may just be missing the magic Google phrase to find this information.
I thought that a bimetallic tube structure might be good for lunar base structure basics.
A large bimetallic sheet is made with folded hooks at each end. The material is such that it can be rolled tightly at warmer temperatures. Locking bands applied. Load a bunch of them onto a lifter to the moon. After it has landed the temperature will be such that the material wants to expand outward from its coiled state. Release the bands and it uncoils. The hook ends engage and you now have a tube. Maybe the hook creases can be filled/coated with a heat activated adhesive. After the coil has expanded and the hooks are engaged, lunarnaughts ( are they? ) can apply heat to activate the adhesive to seal. Now you have a metal tube to work with.
I also envisioned umbrella type inserts in the rolled tube. Maybe attached end to end with a rod. As the tube expands, the umbrella ribs open at the ends of the tube. Ideally they have a flexible material that could also be sealed at the edges. But having a inward edge on the bimetallic sheet does not seem possible to roll up.
Of course this can also be used in space in general. Space station module sections etc…
Bimetallic tube strutures … sounds heavy
The temperature of the moon varies bigly from lunar noon to lunar midnight. More than 600 degrees F across a single lunar “day”. Seems like precisely the type of environment where bimetallic tubes would be an incredibly bad idea. Like, second-hand carbon fiber submarine level bad.
Heavy. Well you have to get something up there. Having it coiled is compact. Bimetallic to self unroll means it is one piece with minimal construction complication. Not several pieces of semi circular structures packed in the lift vehicle.
Temperature. You unfurl it when the temperature is right. It could be coiled under some force on earth at whatever temperature is best. Then released on the moon or in space when the temperature is best.
Temperature…
It would unfurl at an appropriate temperature. Then seal the seam. So it is a tube. But now variations in temperature are going to introduce stresses. So it would be best to have a minimal difference in the metals coefficients of expansion/contraction. Enough that it encourages unfurling. But not excessive that temperature variations after that will stress it a lot. Also, once it has attained tubular aspect, it will have structural resistance to buckling.
Any material will have expansion/contraction issues. The bimetallic one may not have excessive issues.
It is a bonus that the interior will be at positive pressure. So it won’t be subject to crushing. Unlike a submarine.
I do wonder how nice a circular tube it would actually unfurl to. But structures will have a lot of stuff installed into them. Which will require cross bracing and such to mount it. These later pieces can wedge it out to a more nicely circular skin. I propose this as just the basic outer skin tube that can be delivered in a compact and simple way. Not a bunch of preformed curved panel pieces that need to be assembled with various means.
I would expect that the default structures will be inflated with the main support being nothing more than the air pressure inside. All the usual issues will need to be addressed: micro meteoroid resistance, thermal cycling, some level of self healing. But it isn’t going to be all that difficult. Progress has already begun for orbital spaces, and it translates pretty well. Even a pure oxygen environment at 3psi gets you a very rigid structure. Internal spaces and structures can be set up independently of the outer shell. Which affords residents the ability to finish erecting the habitat in a shirtsleeves environment, and long term flexibility of the interior.
The simple nature of erecting an inflatable is going to be hard to beat. Moreover, once pressurised, the dominant loads on any structure are going to be from the internal pressure. So there isn’t great value in bucking the forces with anything else.
Good points.
That would probably be a dome. Smooth an area. Apply some base to it. Then inflate.
A very large area with minimal weight.
But in open space the self expanding tube might be a good option. Space station modules.
I have seen houses made by inflating a dome and spraying concrete over it. Once set, holes can be cut for windows and doors and the inflatable part removed and re-used.
Ideally, the “concrete” would be a chemical foam bulked out with material from the Moon’s surface. Initially, the domes would be fairly small, but they can easily be joined together to make larger spaces. The walls could be made several feet thick, to provide insulation and strength.
The first domes might well be constructed automatically, with no need for human supervision.
I’m trying to fathom what problem the OP thinks bimetallicness specifically will solve. What does that do that ordinary large cross-section pipes, couplings, and end-caps won’t?
I believe the OP plans to unroll the tubes and use them for arched roofs, like a Quonset hut. But habitats on the moon or Mars don’t need a metal roof for protection so the whole concept is moot. Besides, other solutions such as inflatable fabric structures reinforced with local materials will give a much more flexible and expandable structure at massive weight savings.
Isn’t the usual thinking that lava tubes would be suitable habitats?
Lava Tubes are certainly well protected, and have a constant temperature. They are actually ideal habitats. Unfortunately, they are hard to get into. The open skylights we’ve seen are typically 60-80m above the tube floor. And the edges of the tubes are very rough and variegated into layers.
To make a lava tube useful, we’d either have to find one with a side entry where we can walk right in (there are some candidates, but we’re not sure), or we’ll hasve to build some kind of lift structure or stairwell or ramp for getting in and out of the tube.
It’s doubtful that we’ll find a tube small enough and sealed enough to pressurize, so the current thinking is to drop inflatable habs into the tube and live in those. Then you don’t need to worry about radiation, micrometeorites, etc. In fact, you could work in a lava tube in a simple pressure suit without all the extra stuff Apollo astronauts had to wear.
Over time we might be able to seal off small sections and pressurize them if we find enough lunar volatiles - at least enough that you could work in them with an oxygen mask, or maybe enough to grow plants in large spaces.
For the surface, the plan is to use inflatable habitats, then cover them with three feet or so of regolith for protection against micrometeorites, radiation, and to provide insulation against wild temp swings.
If Starship HLS works, we can send some very large equipment to the Moon. The payload bay is 9 meters wide. A 9 meter inflatable habitat could expand to maybe 20-30m in diameter. or 2800-4000 sq feet of living area. You could probably fit several in one Starship.
The bimetallic metal for unfurling is a clever idea, but it won’t work on the Moon because the bimetal would be exposed to too many temperature extremes. Also, after unfurling you’d still have to weld together the rest of the structure. An inflatable habitat gets you the same space-compacting transport design, while expanding into a nice living space. And they can be constructed and pressure tested on Earth, then collapsed and folded and transported to the Moon. Setup there would be simple.
If you want metal tubes and for some reason you have to build them on site, I reckon it wouldn’t be all that difficult to make a machine that takes in a feed of metal in the form of a strip - say 2 inches wide and loops it around to weld it back to itself (like a big spring, but with no gaps, and each coil welded to its neighbour).
Such a machine could be designed to be pretty much an appliance - you feed it with spools of metal strip and welding wire, and continuous tubing of your chosen configurable diameter comes out of the other end. It could even make curved tubing by selectively shaving the side of the metal ribbon to vary its width.
Edit: I bet someone has already invented this.
Another edit: Yep. Spiral welded pipe/duct is a thing - some of the machines are the size of a building, but those are making huge, thick walled pipes
Bimetallic usually refers to a layer of copper inside a tube, coppers a heat reflector hence your bimetallic water bottle can keep it’s contents hot or cold without vacuum inside.
The memory metal or shape metal the OP refers to has been around for ages, normally nickel titanium alloy.
If your silly enough to build on the moons surface a self repairing structure would be handy as you will be hit by meteors without an atmosphere to burn them up.
Bimetallic material is how thermostats work. Differential expansion and contraction causes the material to deform in a predictable way. It’s a different phenomenon to shape-memory alloy.
I’ve never heard of the usage you mention; copper is a very good heat conductor so just coating a metal bottle with it (with no insulating layer) doesn’t seem like it would work at all. Could you link to an example of the bimetallic bottle you’re describing? I can’t find it.
Copper reflects 98% of IR radiation ,your right you need a airgap however a decent stainless steel waterbottle relies on an internal copper coating instead of a vacuum to keep its contents hot or cold, I find it very counterintuitive myself.
Just occurred to me: if you have a large bimetallic sheet and you heat it up, it will deform in both dimensions; if won’t roll up into a tube - it will try to deform into some sort of dish (and this will probably go badly and it will pop into some other shape like a saddle or something)
I’m still not finding the products you are referring to - metal thermos type bottles have a vacuum and a reflective coating (just like glass ones which typically use silver). the vacuum minimises heat loss through conduction (and convection I suppose - there’s no convection in a vacuum); the reflective layer deals with heat loss by radiation