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View Full Version : Inflatable Spacecraft Structure (Transhab style) questions.



Philippe Lemay
2010-Apr-13, 02:35 AM
Arguably this could have gone in the space exploration section... but there are plenty of Bigelow discussion threads there already. Plus I have a specific question regarding this subject.

I was looking at a descriptive vid (on YouTube I think it was), that talked about the upcoming Bigelow spacecraft/station/module thingy. One of the persons working for Bigelow (I think she was an engineer or a technician) said that once fully inflated the module's outer skin would be as hard and as solid as steel. And even that it's ability to resist the kind of damage you would likely to see in space (from radiation and micro-meteorites) will be stronger than conventional plates.

This got me to thinking that this must be a marvelous combination of materials that could revolutionize space exploration as we know it (along with the vehicle we will use to preform those explorations). So much so that in a discussion I was having regarding a sci-fi story concepts with a friend, I suggested the first sizable interplanetary spaceships would use inflatable modules.

He doesn't share my opinion, thinking that the Bigelow engineers are either exaggerating, or they're covering up some kind of terrible down side. The only thing I could think of is that it might take a while to inflate and upkeep, but that seems like peanuts compared to the benefits it offers.

So, yea, are Bigelow exaggerating, and what downsides might there be to the concept? Would it have anything to do with why NASA had so much problems making it work (or did they never get it off the ground because they were just being incompetent?)

mugaliens
2010-Apr-13, 03:08 AM
Got a link to your "descriptive vid?"

It would help...

Philippe Lemay
2010-Apr-13, 03:28 AM
http://www.youtube.com/watch?v=MLfvwMI1XZM

Originally I was somewhat suspicious of all these upstart private companies which I saw as trying to replace NASA. But after seeing Ad Astra's work on the VASIMR... I'm willing to put hope in them. I just wonder how pie-in-the-sky this inflatable idea sounds. Is it sound, or is it still too early to tell (meaning downsides could pop up, we just haven't seen them yet).

EDIT:
Hmmm, actually, this isn't the one where they say the outer skin is stronger than steel. They just say it's stronger than the ISS's hull and is developed from something similar to Kevlar. But I remembering hearing that quote somewhere, I'll keep looking.

IsaacKuo
2010-Apr-13, 02:43 PM
For a given mass, Kevlar is indeed stronger than steel. If you inflate it with 1atm, it won't be as "hard" or rigid as steel, but it will still be very sturdy.

But you can also use composites to make rigid hulls, and these would generally be superior to an inflatable hull (they're also stronger than steel). The big advantage of an inflatable is that you could launch something that's relatively compact from Earth and inflate it to a larger volume in space. For example, a module which inflates to 3x its original diameter will have 9x the original volume.

Philippe Lemay
2010-Apr-13, 03:03 PM
Another thing I liked about the modules is that they use a kind of foam, so that they can take damage and be deformed, and then retake their original shape.

Kind of reminds me of these: http://en.wikipedia.org/wiki/Shape_memory_polymer & http://en.wikipedia.org/wiki/Shape_memory_alloy

I know that people have a deep affinity for having tough spaceships made of metal and alloys, but I'm starting to think that future large spacecrafts might use more foam and composites than any conventional metals. I realize I'm probably being very vague in my description here, by future large spacecrafts I mean vehicles that will be able to transport many people (at least 10) from one planet to another, more than once.

I know I know, could be a VERY long time before we see that, but I'm willing to assuming a century or so of technological and economical development here on Earth. I find it very interesting to wonder what these may eventually be made of.

PraedSt
2010-Apr-13, 03:05 PM
But you can also use composites to make rigid hulls, and these would generally be superior to an inflatable hull (they're also stronger than steel). The big advantage of an inflatable is that you could launch something that's relatively compact from Earth and inflate it to a larger volume in space. For example, a module which inflates to 3x its original diameter will have 9x the original volume.
I'm still trying to make my mind up about inflatables. What would be some of their disadvantages compared to rigid structures?

Philippe Lemay
2010-Apr-13, 03:23 PM
A lot of people seem to fear that a big enough meteor will make it go pop, but I don't think it's that simple. Those walls are something like a foot thick and (as stated earlier) are made out layers of kevlar-like materials.

IsaacKuo
2010-Apr-13, 03:59 PM
I'm still trying to make my mind up about inflatables. What would be some of their disadvantages compared to rigid structures?
There is some penalty in terms of strength for a given amount of mass, but this penalty may be small. More significant may be the practical "space tetris" problem of putting "stuff" into the inflatable structure after inflation. Prefab modules can have everything constructed in place back on Earth. But an inflatable module needs to be inflated first, and then "stuff" needs to be crammed in later somehow.

If you're going to deal with the "space tetris" problem, then one promising alternative to inflatable modules is to use a spent booster tank. This tank will be rigid rather than inflatable because it has to survive flight through the atmosphere, but it represents a huge amount of volume if you can figure out how to put it to good use.

Note that Skylab was originally going to use this idea, but they determined that there was enough capacity to simply send the whole thing up "dry".

PraedSt
2010-Apr-13, 05:29 PM
A lot of people seem to fear that a big enough meteor will make it go pop, but I don't think it's that simple. Those walls are something like a foot thick and (as stated earlier) are made out layers of kevlar-like materials.
One thing I was thinking about was load-bearing. I don't think there would be much in the way of loads, since we're in orbit and not rotating , but frankly I don't know enough of the subject to be sure.

Anyway, these Bigelow modules have an internal, rigid "backbone" of sorts, so I guess the problem, if any, isn't too hard to address.

PraedSt
2010-Apr-13, 05:37 PM
More significant may be the practical "space tetris" problem of putting "stuff" into the inflatable structure after inflation. Prefab modules can have everything constructed in place back on Earth. But an inflatable module needs to be inflated first, and then "stuff" needs to be crammed in later somehow.
I hadn't thought of that. This seems to be one of those problems that are trickier than they look. Thanks.

mugaliens
2010-Apr-14, 01:51 AM
Thanks for the link, Phillipe. :)

It appears to be quite advanced. As for internal structures, they could be made in such a way as to be compact in the center. And frankly, I'm not sure any of the internal structure needs to be metal. Even lockers could be made of fabric, with either zipper or velcro closures.

The interesting thing about the structure is that the air pressure provides the rigidity. Simple padeyes on the inside could be used to support all internal "structures," even if they're made from nothing more than nylon straps attached to various padeyes and under tension.

Or you leave it open as a zero-G playroom. :)

Noclevername
2010-Apr-15, 06:07 AM
One thing I was thinking about was load-bearing. I don't think there would be much in the way of loads, since we're in orbit and not rotating , but frankly I don't know enough of the subject to be sure.

Anyway, these Bigelow modules have an internal, rigid "backbone" of sorts, so I guess the problem, if any, isn't too hard to address.

According to Atomic Rocket (http://www.projectrho.com/rocket/index.html), an inflatable module should work fine swinging on the end of a line at 1G; They link to a .pdf file of a hypothetical interplanetary ship with inflated-module spin gravity here. (http://www.projectrho.com/rocket/rocket3f.html#habitat) If it's tough enough to survive 1 atmosphere of internal pressure, as long as the connecting structure is sturdy enough you can hang meshwork platforms inside and get 3 stories of decking.

As for the meteor problem, it would be less vulnerable to that than a rigid compartment, as it would have more "give"; the skin would flex under impact, dispersing more of the energy.

PraedSt
2010-Apr-15, 09:57 AM
They link to a .pdf file of a hypothetical interplanetary ship with inflated-module spin gravity here. (http://www.projectrho.com/rocket/rocket3f.html#habitat)Hadn't seen that study before. Thanks.

Philippe Lemay
2010-Apr-17, 10:38 PM
Lots of internal volume like that might also be conveniant for hydroponics application...

I'd be tempted to suggest setting the module itself into a spin so that the plants can experience a semblance of gravity (assuming a cylindrical module, which is usually the case) no doubt aiding in their growth and produce. But realistically... that would require a LARGE module.

Philippe Lemay
2010-Apr-22, 11:56 PM
I just found out that the video is deceptive... it compares the module's diameter increase as being a "pencil that turns into a coke can", which would imply the diameter expanding 5 fold (at least). But upon browsing wikipedia (http://en.wikipedia.org/wiki/Genesis_I#Spacecraft_history)... I found that the prototypes only go from 1.6 meters to 2.54 meters. Which is about 160% increase compared to the payload faring.

The biggest payload faring I could find was a hypothetical one for the Ares V, at 10 meters in diameter. So the biggest module we could get into orbit with near-term technology and infrastructure (assuming we do wind up getting some kind of heavy lifter) would be 16 meter in diameter. That sound about right?

Boratssister
2010-Apr-23, 09:08 AM
This looks like very exciting technology, lets hope its practical.

One day in the future these inflatable ships could be huge. Inflated with something like hydrogen at ground level, then floated up to the top of the atmosphere. Rockets could then take this huge light machine into orbit, to travel the solar system. In space I imagine these machines will have compartments, like a link of sausages.

Philippe Lemay
2010-Apr-23, 01:26 PM
Uh... that's unlikely. The prospect of floating a balloon into orbit was brought up in other threads already. Basically the problems are orbital velocity and air friction. Because of practical limitations, even if you used hydrogen, you would never be able to make it past 50 kilometers, not with any kind of appreciable payload. And while you might be able to reach a good 12 kilometers up, your module won't be travelling fast enough laterally to maintain an orbit. The rocket doesn't just go up, it also speeds up so that it's moving along it's orbit at something like 7 kilometers a second.

And yea, if you inflate it inside of an atmosphere, then right away you've eliminated all of the benefits of using an inflatable module. A small payload volume in the atmosphere means that you reduce air friction and make it easier to get the thing up and out of the atmosphere.

Boratssister
2010-Apr-23, 03:20 PM
Uh... that's unlikely. The prospect of floating a balloon into orbit was brought up in other threads already. Basically the problems are orbital velocity and air friction. Because of practical limitations, even if you used hydrogen, you would never be able to make it past 50 kilometers, not with any kind of appreciable payload. And while you might be able to reach a good 12 kilometers up, your module won't be travelling fast enough laterally to maintain an orbit. The rocket doesn't just go up, it also speeds up so that it's moving along it's orbit at something like 7 kilometers a second.

And yea, if you inflate it inside of an atmosphere, then right away you've eliminated all of the benefits of using an inflatable module. A small payload volume in the atmosphere means that you reduce air friction and make it easier to get the thing up and out of the atmosphere.

I was thinking about floating rockets up , maybe around the edge of this giant balloon and once at the highest altitude the rockets would ignite........ I did say way into the future , may be, possibly? May be not.

Philippe Lemay
2010-Apr-23, 10:56 PM
Like I said, the highest you would probably reach (with rockets and payload dragging you down) is probably 12 kilometers. That's still leaves plenty of atmosphere on top of you that would cause friction against the module.

To really use the module as both an assistance for floating to a higher altitude and for a living space in orbit, you would need to inflate to ascend, deflate and repack it into it's small volume to reduce drag (while simultaneously igniting the rockets), and then in orbit re-inflate it once more.

It MAY be possible, but it sounds a little crazy. I don't think these inflatable modules were ever intended to serve as high altitude balloons.