3 ms·

I think there are lots of possibilities for inflatable vehicles which cannot be deflated. For example, make a flimsy structure out of thin steel foil, then pre

I think there are lots of possibilities for inflatable vehicles which cannot be deflated. For example, make a flimsy structure out of thin steel foil, then pressurize it to give it far more strength than it would otherwise have. Same as the strength of a coke can. Except with steel as the tensile material, you can probably use pressures up around 1000 psi, making the whole structure have an amazing strength to weight ratio.

Gare 3y ago
> Except with steel as the tensile material, you can probably use pressures up around 1000 psi, making the whole structure have an amazing strength to weight ratio. Congratulations, you have created a bomb.
- londons_explore 3y ago
  You certainly need to think about that in the design. But by rolling a 'texture' into the sheets the structure is made from, you can make sure that any hole can't 'rip' bigger, and therefore fails slowly rather than rapidly. You also need pressure regulator valves in case of fire. And you might want to make the whole thing double or triple skinned so the highest pressures can be deeper inside where they are less likely to get punctured/less vulnerable to corrosion damage/crash damage.
  - usrusr 3y ago
    But when do you really need a structure that has this exceptional strength on the happy path, but would still be good enough in terms of safety when pressure is lost? Unmanned aviation comes to mind, but the ratio between structural mass and battery+payload is already so low, even a zero-mass structure would not make a meaningful performance difference. It's all about the battery tech. Scaling up foil boating perhaps? Carbon fiber construction would certainly appear like a good candidate for taking advantage of being pressurized, and I perhaps naively take it as a given that materials is the major limiting factor in scaling up.
    - londons_explore 3y ago
      > still be good enough in terms of safety when pressure is lost? You might not design for that case. A suspension bridge can't survive a tower falling over, or a cable snapping. The pressurized structures wouldn't be able to survive leaks over X size, and for leaks under X size, compressors would be used to maintain pressure.
    - londons_explore 3y ago
      Rockets are the obvious use. The structure of a rocket is far heavier than the payload, and every kilo of weight you can shave off the rocket, you can add to the payload.
      - deleted 3y ago
        [deleted]
  - buran77 3y ago
    At that point you're not dealing with a "flimsy structure out of thin steel foil" that you can inflate to hundreds of psi. You described what's basically a submarine, multiple high and low pressure hulls able to withstand hundreds of psi of pressure. Just for some reference, 1000psi is the kind of pressure you get ~700m depth (2300ft), double what a submarine would regularly withstand. Pressure in your average propane gas tank probably peaks around 200psi in high temperature. That steel isn't flimsy, it tends to get bulky and heavy even with creative ribbing and reinforcement. It has to make a lot of sense practically and economically to consider such an option. So it ends up being used in places where weight or cost matter less.
    - londons_explore 3y ago
      A CO2 fire extinguisher is about 1000 psi.
      - buran77 3y ago
        A 1000psi fire extinguisher uses ~5mm thick steel even for that relatively small diameter cylinder. A typical extinguisher is ~200ish psi with a wall probably ~1mm thick. This highlights that high pressure and "thin steel foil" do not go well together and don't scale in your favor. Pressure makes any failure considerably more dangerous.
- rbanffy 3y ago
  Wasn’t the Centaur upper stage pressurised. I remember an incident where one collapsed under load because the tank lost pressure.
  - GuB-42 3y ago
    Well, rockets are essentially bombs we try to make explode in a controlled manned. The "controlled" part is not always successful. Fueled rockets are treated like live bombs. No one around except for people who really need to be (like astronauts).
    - dylan604 3y ago
      > The "controlled" part is not always successful. I'm assuming you're referring to the unnominal situations resulting in the unscheduled rapid disassembly procedures? I wonder how many people watch launches with similar intent as NASCAR races where they're just looking for the crashes or hockey games looking for the fights?
      - GuB-42 3y ago
        I must admit I tend to watch SpaceX test flights for the potential fireworks. But for, say the JWST launch, it really wasn't with the same intent. In the former, it is just SpaceX way of doing business, no big deal, no significant payload being destroyed and the next rocket is on the line. The latter is the result of billions of dollars, many years of work and great scientific promises that could be blown to pieces. And of course, for manned flight, who in their right mind wants astronauts dead?
        dylan604 3y ago
        > And of course, for manned flight, who in their right mind wants astronauts dead? Which begs the question, who wants to fly Starliner?
        rbanffy 3y ago
- whamlastxmas 3y ago
  Especially if Boeing is involved
scubazealous 3y ago
It would be cool, especially with advances in plastics you could layer over the steel to protect it from corrosion like what they do with soda cans. For reference, a steel or aluminum SCUBA tank is usually filled to 3000psi and when I fill steel tanks I can hear and sometimes see the metal start to slightly balloon. This is normal because steel is not brittle but it is very strong. There is a lot of rules put in place for safety though. A tank has to be visually checked by a professional every year and hydro statically tested every 5. The danger is any rust/corrosion weakening the metal and causing it to rupture. More often seen in aluminum tanks, which is one reason I prefer steel.
- marcosdumay 3y ago
  Yes, in theory steel is not the best material for a high-pressure tank. We use it because it's cheap and well tested. But we are probably better of with a layered combination of a few different materials. Steel may not even enter it.
  - nradov 3y ago
    Steel is the best material for certain scuba applications due more to buoyancy characteristics than strength. Firefighters typically use composite tanks for SCBA now, which are stronger but too buoyant for diving. Layers of dissimilar materials are often problematic due to galvanic corrosion, different rates of heat expansion, and water intrusion between layers.

Gare 3y ago

> Except with steel as the tensile material, you can probably use pressures up around 1000 psi, making the whole structure have an amazing strength to weight ratio. Congratulations, you have created a bomb.

londons_explore 3y ago
You certainly need to think about that in the design. But by rolling a 'texture' into the sheets the structure is made from, you can make sure that any hole can't 'rip' bigger, and therefore fails slowly rather than rapidly. You also need pressure regulator valves in case of fire. And you might want to make the whole thing double or triple skinned so the highest pressures can be deeper inside where they are less likely to get punctured/less vulnerable to corrosion damage/crash damage.
- usrusr 3y ago
  But when do you really need a structure that has this exceptional strength on the happy path, but would still be good enough in terms of safety when pressure is lost? Unmanned aviation comes to mind, but the ratio between structural mass and battery+payload is already so low, even a zero-mass structure would not make a meaningful performance difference. It's all about the battery tech. Scaling up foil boating perhaps? Carbon fiber construction would certainly appear like a good candidate for taking advantage of being pressurized, and I perhaps naively take it as a given that materials is the major limiting factor in scaling up.
  - londons_explore 3y ago
    > still be good enough in terms of safety when pressure is lost? You might not design for that case. A suspension bridge can't survive a tower falling over, or a cable snapping. The pressurized structures wouldn't be able to survive leaks over X size, and for leaks under X size, compressors would be used to maintain pressure.
  - londons_explore 3y ago
    Rockets are the obvious use. The structure of a rocket is far heavier than the payload, and every kilo of weight you can shave off the rocket, you can add to the payload.
    - deleted 3y ago
      [deleted]
- buran77 3y ago
  At that point you're not dealing with a "flimsy structure out of thin steel foil" that you can inflate to hundreds of psi. You described what's basically a submarine, multiple high and low pressure hulls able to withstand hundreds of psi of pressure. Just for some reference, 1000psi is the kind of pressure you get ~700m depth (2300ft), double what a submarine would regularly withstand. Pressure in your average propane gas tank probably peaks around 200psi in high temperature. That steel isn't flimsy, it tends to get bulky and heavy even with creative ribbing and reinforcement. It has to make a lot of sense practically and economically to consider such an option. So it ends up being used in places where weight or cost matter less.
  - londons_explore 3y ago
    A CO2 fire extinguisher is about 1000 psi.
    - buran77 3y ago
      A 1000psi fire extinguisher uses ~5mm thick steel even for that relatively small diameter cylinder. A typical extinguisher is ~200ish psi with a wall probably ~1mm thick. This highlights that high pressure and "thin steel foil" do not go well together and don't scale in your favor. Pressure makes any failure considerably more dangerous.
rbanffy 3y ago
Wasn’t the Centaur upper stage pressurised. I remember an incident where one collapsed under load because the tank lost pressure.
- GuB-42 3y ago
  Well, rockets are essentially bombs we try to make explode in a controlled manned. The "controlled" part is not always successful. Fueled rockets are treated like live bombs. No one around except for people who really need to be (like astronauts).
  - dylan604 3y ago
    > The "controlled" part is not always successful. I'm assuming you're referring to the unnominal situations resulting in the unscheduled rapid disassembly procedures? I wonder how many people watch launches with similar intent as NASCAR races where they're just looking for the crashes or hockey games looking for the fights?
    - GuB-42 3y ago
      I must admit I tend to watch SpaceX test flights for the potential fireworks. But for, say the JWST launch, it really wasn't with the same intent. In the former, it is just SpaceX way of doing business, no big deal, no significant payload being destroyed and the next rocket is on the line. The latter is the result of billions of dollars, many years of work and great scientific promises that could be blown to pieces. And of course, for manned flight, who in their right mind wants astronauts dead?
      - dylan604 3y ago
        > And of course, for manned flight, who in their right mind wants astronauts dead? Which begs the question, who wants to fly Starliner?
        rbanffy 3y ago
whamlastxmas 3y ago
Especially if Boeing is involved

scubazealous 3y ago

It would be cool, especially with advances in plastics you could layer over the steel to protect it from corrosion like what they do with soda cans. For reference, a steel or aluminum SCUBA tank is usually filled to 3000psi and when I fill steel tanks I can hear and sometimes see the metal start to slightly balloon. This is normal because steel is not brittle but it is very strong. There is a lot of rules put in place for safety though. A tank has to be visually checked by a professional every year and hydro statically tested every 5. The danger is any rust/corrosion weakening the metal and causing it to rupture. More often seen in aluminum tanks, which is one reason I prefer steel.

marcosdumay 3y ago
Yes, in theory steel is not the best material for a high-pressure tank. We use it because it's cheap and well tested. But we are probably better of with a layered combination of a few different materials. Steel may not even enter it.
- nradov 3y ago
  Steel is the best material for certain scuba applications due more to buoyancy characteristics than strength. Firefighters typically use composite tanks for SCBA now, which are stronger but too buoyant for diving. Layers of dissimilar materials are often problematic due to galvanic corrosion, different rates of heat expansion, and water intrusion between layers.