Zeppelins in space?

Discussion in 'General Science & Technology' started by MetaKron, Jul 4, 2006.

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  1. MetaKron Registered Senior Member

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    If you build a spacecraft on the ground it has to be able to withstand not only the full force of the Earth's gravity but also at least two more gravities on take-off. There is a huge weight penalty when you design any large structure to be lifted that way. This translates to a hell of a lot of money and very sharp limits on the size of the spacecraft.

    I've seen inflatable technology laughed at affectionately in comics online. Still, it has a lot going for it. Not only are inflatable structures easy to carry, they are cheap to make. Even cheap aluminum panels are a lot more expensive per square foot than inflatable materials like neoprene that can hold air for long periods of time. We even have materials like mylar that can withstand vacuum quite well and have become commodities, and these aren't so hugely expensive.

    There are all sorts of ways that inflatable enclosures could be useful in space. They could be parking garages for space shuttles. Imagine being able to replace tiles and otherwise service the vehicle in shirtsleeves. Repairs would go a lot faster and cause a lot less stress. There could be huge supply depots and refuges where astronauts could go if their ship malfunctioned but they could still somehow reach the emergency shelters, if necessary using improvised sleds, or even sleds that they could take out of storage that had the capacity to move them from orbit to orbit, sort of broomsticks with rockets, batteries, and oxygen.

    The thing I have on my mind is the idea of sending up a gas bag for the outside, then building the framework for it from the inside, that framework arriving folded up. This is actually something that a bright person can build under Earth's gravity from scratch, a lot like building a geodesic dome from a kit, maybe with someone to help with the lifting. Anyway, design the beginnings of the internal structure to unfold inside the gas bag and become the rigging that workers can run around inside. Then build it up a lot like a zeppelin. Figure out a way to get the internal structure to fit snugly inside the gasbag, like telescoping poles. I'm thinking inflatable balls at the ends of the poles to press against the inside of the big bag, or inflatable inner-tube like structures. Or, the gas bag could be laminated from the inside to make it rigid, the original envelope being the mold for the final form of the hull. Double-bag the thing for safety. Divide it up into airtight compartments for the same reason.

    Use this as the model for the first interplanetary ships. When you have millions of cubic feet to work with for a penny or less per cubic foot, all sorts of things become possible. You've saved the expense of building and lifting a million tons of hardware. Then think what you can do with those savings. Extra atmosphere and supplies goes without saying. Use more gasbags as storerooms. Pack them with electronics components, oxygen generators, batteries, lights, tools, nuts, bolts, and other fasteners, food, medical supplies, everything. The scheme does include a sturdy endoskeleton to hold everything in place during acceleration.

    There could be a huge volume devoted to a fleet of surface-to-orbit craft that could land on and take off from most planetary bodies that are not Earth, Venus, or gas giants. I can see sending up a whole stack of them on a heavy lifter. Carefully pack a couple of dozen of them, send them up, put the whole upper stage inside the balloon and unwrap them there.

    This could save a billion dollars on space suits alone, space suits only being able to be worn a dozen times and costing more than a million dollars each.
     
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  3. Oli Heute der Enteteich... Registered Senior Member

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    No. Providing you generate more than 1G of lift/ thrust then you're going to reach orbit (eventually).
    Okay, you have very large inflatable structures in orbit - how do you prevnt tearing and punctures? Especially if you're saving money on space suits. You still need a minimum of one per person in case of emergency.
    What about radiation shielding?
    You'd probably have to develop a new material capable of withstanding the pressure differential (can't find any solid figures on the mechanical properties of neoprene except a general statement that it's useful "when pressure are low" http://www.thomasregister.com/olc/33727371/page7.htm but still looking), and temperature differentials without becoming brittle.
    Not knocking the general idea as a "rescue base" or temporary setup, but I doubt astronauts would be happy inside what is no more than a giant balloon - pyschologically it wouldn't do much for their sense of survival

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  5. MetaKron Registered Senior Member

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    Two spacesuits per person run a lot cheaper than possibly dozens of spacesuits per person. They last longer when not in use and emergency suits can be a lot cheaper than suits made for working EVA. A good part of the idea is to do as much work as possible in a shirtsleeves environment. Your work suit costs less than a hundred dollars instead of millions.

    The amount of acceleration that a structure would have to survive depends on how much fuel you have to throw away to accelerate it to orbital velocity. I'm going with three gravities as a low end. Fuel costs still decrease substantially while payload increases when you go to five gravities of acceleration. I'm talking about using current booster technology. You know very well that the cost of fuel to lift a structure at a fraction above G is extremely high, and so is the cost of the structure that carries the increased amount of fuel.

    How do you prevent tearing and punctures with steel or aluminum? Both of those materials peel away really easily. When you have a wind blowing really hard, it can rip a steel wall like paper. This isn't something that it can do to a material that is supported by long, strong fibers in any sort of criss-crossing patterns. It seems entirely credible to me that such a fabric can be harder to tear than steel.

    You only need radiation shelter during storms, and storm shelters can be made within the water that the ship will have to carry. It will probably carry water for propellant. I would rather see them find a way to build a high specific-impulse engine that uses water than try to build one using cesium or some other material that cannot also be used as a supply of oxygen. You can throw anything through a plasma torch or an ion engine. The speed at which the material is ejected is a lot more important than its atomic or molecular weight. The thrust developed is linearly proportional to the molecular weight of the propellant and it is proportional to the square of the speed at which the propellant is exhausted.

    I don't think that neoprene is all that good against vacuum. I don't even have a good idea what is the best, but Kevlar was developed for the space program. I think we need a self-healing material that will actually sort of anneal itself to the surface that it is bonded to under the sun's rays, and that's going to take some doing. I might hypothesize a material with properties that allow it to flow across the fabric when it is heated, form a smooth surface, but has a high enough surface tension to keep atmosphere from leaking. Once someone asks that question someone else may find a way to answer it. There should be a glass or graphite fiber base that is as impervious as possible, and there needs to be a way to patch it.

    We know there are vacuum-resistant composites out there and mylar is good in vacuum. An inflatable does not have to be like a toy ballon that stretches when inflated. It can be a fabric that does not stretch but is flexible and can be stored folded and flat (watch the creases!).

    Sleeping quarters and some commons areas should be vacuum proof in their own right and be used if the outer envelope fails. I think it would also be beneficial to have vacuum pumps to scavenge atmosphere from the outer envelope if failure is detected, once the astronauts are safe. Waste not, want not, and there is no danger of collapsing the envelope by vacuuming it out. We are talking about possibly millions or billions of cubic feet. I think that I also mentioned dividing the ship up into cells so that emptying one cell compromises only a small percentage of the ship. Circumstances that cause more than two punctures at a time are supposedly rare. Some thought should also be given to materials that can be applied to the outside to absorb the impact of micrometeorites and prevent punctures.

    At some point the sheer volume of the gas bag will be some protection. You might have hours instead of seconds to respond before a costly amount of air has been lost.

    The astronauts could of course learn to live with it, but once you have an atmosphere and a framwork, they can build what they want inside of it. If they choose it can be independently proofed against vacuum and the bag is just the first line of defense against the vacuum. I've always liked layered defenses. All construction work inside will go much faster and cheaper with much greater comfort. Imagine being able to set a wall panel within minutes instead of several hours.

    I don't even know that there would be benefits to eventually removing the bag in most cases, but something like this should be used as a spacecraft/space station factory. "Snap-together" designs should be assembled in zero gravity and in an atmosphere, making it possible for a person using a small work area, maybe nothing more than an area set apart by a net, to assemble an interplanetary craft from a kit in a few hours. The ship would be something with a few hundred feet of internal space, propulsion, life support, navigation, and the usual odds and ends. It would be good for prospecting the asteroids or shuttling a few people from one orbit to the next.

    Basically, I think that this is a cheap way to gain a foothold in space that will allow us to start expanding our capabilities rapidly.
     
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  7. Oli Heute der Enteteich... Registered Senior Member

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    Yeah, but they don't rip the way a fabric would. Okay, rip-stop types are available, but generally permeable - development time.
    Nope, you need protection against the generally higher level of radiation (no thickness of atmosphere, remember).
    Nope. Developed sort of "by accident", it was described at one point as a material looking for an application - and radial tyres were one of its first uses.
    Umm, if you're working inside a balloon how do you anchor work stations, beds control panels etc? You'd need a rigid structure inside to keep all of those things in the same relative position to each and the external structure, surely?
    Ah, okay I think I may have misunderstood your intial premise, or you're swinging round to my way of thinking. But I do think you may be onto something here... keep going.
     
  8. MetaKron Registered Senior Member

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    I already said that it should have a rigid structure inside. That's why it's a zeppelin, not just a gasbag.

    Considering what can be done with flexible materials, and the advantages, unless we are expecting a surprise attack by the Klingons I think that some stations and ships will never find the bags obsolete.
     
  9. Oli Heute der Enteteich... Registered Senior Member

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    Yep, but a rigid structure on the inside for location purposes (of work stations etc) would have to be MUCH closer together than the one required merely for structural strength. But you could use the structural internals to anchor the utility internals, and then add panelling to stop stuff going between the utility units and the inside face of the bag. Eventually end up with a room surrounded by the bag, but mostly not visible.
     
  10. MetaKron Registered Senior Member

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    I thought that was pretty much what I was saying. Now, a lot of the dividers between spaces can be of material that comes on rolls. A lot depends on how reliable or durable the bag is considered to be. It might be good for twenty years then it may have to be replaced. Perhaps it could eventually become a geodesic bubble with titanium from the moon for the panels. Perhaps all living quarters and everything that had to be protected from the vacuum could be made vacuum-resistant to begin with, or very early in the game. Then doing the changeovers would be much easier. In between times, the station is good for bringing in moderately large objects like space shuttles for servicing and for building ships for interplanetary travel. Imagine being able to build that ship on a work-floor in space that is of whatever size you need, then being able to just shove it out the airlock when it's ready. Let's see foam try to fall off of THAT.

    One really funny thing about the solar system is that it contains over a hundred large bodies that are accessible using reusable spacecraft that can land and take off again, not counting the thousands of asteroids. Even more major bodies like Mars, Mercury, and the Moon are accessible that way, and the ability to build those craft in space is extremely valuable. At the very least, the ability to service them in space is that valuable.

    I do keep thinking that cheap reusable rockets on Earth are possible, considering advanced in technology. But still, ships that float carry a lot more tonnage than ships that fly in the air. Large carriers in space are the ships that float. They can drop-ship tons of materials at almost no cost. I think that the best route to the large carriers includes inflatable ships and space stations.

    This will also tend to prove my point that we not only need the technical expertise that a more advanced race might have, we need the ability to manufacture large structures, which Earth humans do have.
     
  11. Fraggle Rocker Staff Member

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    I doubt that inventing a material that can withstand a pressure differential of only one atmostphere will be much of a technical challenge.
     
  12. Oli Heute der Enteteich... Registered Senior Member

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    I wouldn't have thought so either - providing it's flexible enough to stow folded and not so permeable that air is going to need replacing at a ridiculous rate. And withstand the temperature differentials without brittling/ degrading. There's maybe something available already, but it just hasn't been publicised in that direction.
     
  13. MetaKron Registered Senior Member

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    Mylar has been here for forty years give or take. There is all sorts of stuff out there, like beta cloth and silicone. Adding composite fibers in a fashion not entirely unlike the new Glad bags would prevent these bags from ripping when punctured.
     
  14. Oli Heute der Enteteich... Registered Senior Member

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  15. superluminal . Registered Senior Member

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    I just like the thread title.

    Zeppelins in Space space space space space space space......

    Filmed in ((( CINEMASCOPE )))

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  16. Oli Heute der Enteteich... Registered Senior Member

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    You probably liked the Muppet series as well:


    Piiiiigs iiiin spaaaace.
     
  17. superluminal . Registered Senior Member

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    Yup!
     
  18. MetaKron Registered Senior Member

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    Whatever the permeability, the larger the volume enclosed the less of that volume is lost each day. The ratio of volume to surface area is greater. You lose a smaller percentage of what you have.

    People don't realize that gas will also pass through steel and aluminum.
     
  19. CANGAS Registered Senior Member

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    Around about 1950, give or take, the USAF did highly classified work on the concept of extremely high altitude balloons supporting surprisingly large disk shaped observation stations, carrying multiple person crews, intended to hover for extended periods.

    It is not too much of a stretch to go from the old UASAF plan of floating at, say, 150,000 feet to your plan of finishing the job and propelling into orbit.

    The USAF work was published just a very few years ago in one of the popular science magazines, sorry, don't remember which.
     
  20. MetaKron Registered Senior Member

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    Cangas, it simply won't make orbit unless someone develops antigravity. There's too much air friction even at that height. If any sort of atmosphere provides any useful support, you still have to deal with friction at several times the speed of sound.
     
  21. spidergoat Valued Senior Member

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    I think inflatable structures have been used in space. The biggest drawback that I can think of is resistance to puncture from space debris, which can be tiny, but moving at incredible (relative) speeds.
     
  22. MetaKron Registered Senior Member

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    It's not much of a drawback when the fabric can carry substances on the outside that can shield the fabric better than the space shuttle's skin.
     
  23. kazakhan Registered Abuser Registered Senior Member

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    I think water would be better than gas, particularly if we could get it from the moon. We could fill an inflatable structure with water. It could serve as the outer hull and radiation shield as well as providing drinking water and oxygen of course. An inner hull of conventional materials would still be needed.
     
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