Author Topic: Are inflatable modules even necessary for private space stations?  (Read 33991 times)

Offline Dalhousie

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No, it is to create as much volume as possible because people are going to live in that volume for months, especially if the module is intended to be an option for deep space missions.

For launching space station modules, most launchers are fairing limited, not mass limited. The non-expanded BA-330 can just barely fit inside the standard fairing of the Falcon Heavy, even though it is only half of the maximum payload mass-wise. If you're going to send up anything with a decent volume in a single launch on a reasonably cheap rocket, inflatable modules are very nice to have.

You don't need as much volume as possible, you need enough volume, which is about 20m3 per person free volume.  Current space station modules are not volume limited, but mass limited.
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Offline Dalhousie

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Actually not Kevlar but rather Vectran which NASA has lots of experience with. Spacesuits (EMU)among other things. So far as I have been able to discover there is no aluminum in the BA skins. In fact the lack of aluminum is one of the advantages since there is no secondary radiation generated thus reducing overall radiation exposure.

The secondary radiation issue is, I suspect over stated as all materials will generate some secondary radiation and even an inflatable willcontain a substantial amount of structural and system aluminium.  Besides, aluminium is used for radiation shielding, so is hardly a viability.
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Offline WindnWar

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The Bigelow modules are tougher than aluminum cans as people have posted.

Since "alunimium cans" have hardly proved fragile in space flight and how well the Genesis modules have stood up to spacelfight is not public knowledge AFAIK, I would see this as an unsubstantiated claim by the advocates.


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They will not want the BA 300's fully outfitted as the occupants will bring their experiments. The racks will be based on current ISS racks.

Which meands that all claims about the supposed mass advantages on inflatbale structures are specious.

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And the ISS modules were not fully equipped but, if memory serves, it was mass limitations.

Some were, some weren't.  But I find it strange how fitting something out in space is a parsed as an advanatage for inflatables and a fault for rigid structures

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Also, like it has been posted, BA 300 is designed plus, as I understand it, being constructed. Any ISS type module hasn't bent metal yet. Time is money.

Is BA330 being built?  There are lots of mockups.

You seem to disregard any info that validates the inflatable design for a preconceived notion that its a fad or won't succeed. We know the Genesys modules are still on orbit, and have been for years now. I would assume NASA has far greater insight into them as part of the BEAM module as it was probably used to validate it before launch. They are mass efficient, space efficient and from the models, should be more resistant to mmd strikes and radiation, all of which the BEAM module will help validate. No one is rushing into this, and since the only country currently building any station modules currently besides Bigelow is China, it is currently the only company keeping skills in place for modules. None of these are really debatable.

We will know in a couple years a lot more info on how BEAM fairs and that will likely drive the direction things are headed. But just because it seems odd, that's a rather strange reason to simply disregard all the info that has been presented to you.

Offline Norm Hartnett

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Actually not Kevlar but rather Vectran which NASA has lots of experience with. Spacesuits (EMU)among other things. So far as I have been able to discover there is no aluminum in the BA skins. In fact the lack of aluminum is one of the advantages since there is no secondary radiation generated thus reducing overall radiation exposure.

The secondary radiation issue is, I suspect over stated as all materials will generate some secondary radiation and even an inflatable willcontain a substantial amount of structural and system aluminium.  Besides, aluminium is used for radiation shielding, so is hardly a viability.

Most of your objections to inflatables require more research but the radiation question is rather easy to examine. Lets conduct a little thought experiment;

If we have two modules that are exactly equal in size and contain exactly same racks/wiring/experiments/etc one constructed with an aluminum skin and one with a BA skin the one with the aluminum skin would always be the more dangerous as it would always produce more secondary radiation.

Aluminium is only used for radiation shielding by NASA by default due to weight. Most sources I've been able to find agree that aluminium is a terrible shielding material, especially for X-rays, Gamma Rays, Solar Energetic Particles, Solar Particle Events, and Galactic Cosmic Rays. Our astronauts already have limited lifetimes in LEO and the situation only gets worse the further from Earth we get.

Are inflatables necessary for private space stations? No.

Are they safer and cheaper? Quite possibly, that's what we're trying to find out.
“You can’t take a traditional approach and expect anything but the traditional results, which has been broken budgets and not fielding any flight hardware.” Mike Gold - Apollo, STS, CxP; those that don't learn from history are condemned to repeat it: SLS.

Offline JasonAW3

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The Bigelow modules are tougher than aluminum cans as people have posted.

Since "alunimium cans" have hardly proved fragile in space flight and how well the Genesis modules have stood up to spacelfight is not public knowledge AFAIK, I would see this as an unsubstantiated claim by the advocates.

There are numerous Nasa videos that seem to indicate otherwise.  There are tests that have been done that have indicated that a hit from even a pebble sized meteor could cause substantile damage to the ISS, versus the Bigelow module which gives and deforms much like bullet resistant body armor does.  Currently, Nasa is using, what in effect is, Spaced Armor to mitigate debris damage.  While this has proven effective in the past, even they admit that it's not perfect.  Neither is the Bigelow Module either, but it can take a more sizable impact than could the ISS before potentile pressure failure.

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They will not want the BA 300's fully outfitted as the occupants will bring their experiments. The racks will be based on current ISS racks.

Which meands that all claims about the supposed mass advantages on inflatbale structures are specious.


Comparing Apples to Apples, the same volume for the BA330 is far lower in mass than a comparable volume of current ISS modules.

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And the ISS modules were not fully equipped but, if memory serves, it was mass limitations.

Some were, some weren't.  But I find it strange how fitting something out in space is a parsed as an advanatage for inflatables and a fault for rigid structures

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Also, like it has been posted, BA 300 is designed plus, as I understand it, being constructed. Any ISS type module hasn't bent metal yet. Time is money.

Is BA330 being built?  There are lots of mockups.

Actually, as I understand it, yes, two modules have been currently constructed and one is being used for destructive testing.  Pushing the design boundries until they break.
« Last Edit: 04/01/2015 05:38 pm by JasonAW3 »
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Offline Dalhousie

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The Bigelow modules are tougher than aluminum cans as people have posted.

Since "alunimium cans" have hardly proved fragile in space flight and how well the Genesis modules have stood up to spacelfight is not public knowledge AFAIK, I would see this as an unsubstantiated claim by the advocates.

There are numerous Nasa videos that seem to indicate otherwise.  There are tests that have been done that have indicated that a hit from even a pebble sized meteor could cause substantile damage to the ISS, versus the Bigelow module which gives and deforms much like bullet resistant body armor does.  Currently, Nasa is using, what in effect is, Spaced Armor to mitigate debris damage.  While this has proven effective in the past, even they admit that it's not perfect.  Neither is the Bigelow Module either, but it can take a more sizable impact than could the ISS before potentile pressure failure.

A pebble sized meteor is huge.  A very much doubt a Bigelow inflatable will survive that either.  remember two that a Bigelow module still has a lot of external equipment such as antennae, solar panels and radiators which will be just as vulnerable as a those of conventional station.

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Is BA330 being built?  There are lots of mockups.

Actually, as I understand it, yes, two modules have been currently constructed and one is being used for destructive testing.  Pushing the design boundries until they break.

Thank you.
Apologies in advance for any lack of civility - it's unintended

Offline Burninate

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The Bigelow modules are tougher than aluminum cans as people have posted.

Since "alunimium cans" have hardly proved fragile in space flight and how well the Genesis modules have stood up to spacelfight is not public knowledge AFAIK, I would see this as an unsubstantiated claim by the advocates.

There are numerous Nasa videos that seem to indicate otherwise.  There are tests that have been done that have indicated that a hit from even a pebble sized meteor could cause substantile damage to the ISS, versus the Bigelow module which gives and deforms much like bullet resistant body armor does.  Currently, Nasa is using, what in effect is, Spaced Armor to mitigate debris damage.  While this has proven effective in the past, even they admit that it's not perfect.  Neither is the Bigelow Module either, but it can take a more sizable impact than could the ISS before potentile pressure failure.

A pebble sized meteor is huge.  A very much doubt a Bigelow inflatable will survive that either.  remember two that a Bigelow module still has a lot of external equipment such as antennae, solar panels and radiators which will be just as vulnerable as a those of conventional station.


Offline jongoff

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My take is somewhat similar to Dalhousie's original response--Inflatables aren't necessary for commercial space stations, and the jury is still out on whether they really are superior. I think the main reason so many people seem to think they are is that the only private space station company that has had serious money was Bigelow, and inflatables was the approach they took. But really, I think there are plenty of advantages to using normal aluminum in a LEO application, especially if you build the module integral with the Payload Fairing OML (maybe with some MMOD-MLI on the outside). You can't get quite the same volume, as you can with a max case inflatable, but your structure is likely lighter, and might be easier to pre-integrate. I did a blog post on the topic a few months ago: http://selenianboondocks.com/2014/10/integral-payload-fairing-habitats/

But as I said, the jury is probably still out--inflatables might be better in some cases, all cases, or almost no cases. Not enough experience to really tell at this point.

But I do think that automatically assuming that commercial space stations means Bigelow is premature. I hope they're successful, but I also hope someone else finds a way to compete with them. I'm no fan of monocultures.

~Jon

Offline Norm Hartnett

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After some thought I realized that the answer to your original question “Are inflatable modules even necessary for private space stations?” is, self-evidently, yes.

Why? Because no other private party is attempting to create a space station of any kind. No other private party has spent significant money nor have they orbited one, let alone two, test space craft. No private party has talked NASA into testing a prototype on the ISS.

Why? Economics and vision. (I believe.)

Inflatable modules are necessary for private space stations because no one else is building any other sort of private space station.

“if there is a business case for private space stations, why these would be necessary?”

Because Bigelow Aerospace is the only one building private space stations and inflatables are what they believe will work. Presumably they know what they're doing.

I suspect that's not the answer you were looking for but it is the reality.

BEAM probably isn't necessary to BA's business plan but it certainly can't hurt and may provide a kick start to investment and customer orders.

Edit: I see Jon reached a similar conclusion about the same time I did.
« Last Edit: 04/02/2015 03:17 am by Norm Hartnett »
“You can’t take a traditional approach and expect anything but the traditional results, which has been broken budgets and not fielding any flight hardware.” Mike Gold - Apollo, STS, CxP; those that don't learn from history are condemned to repeat it: SLS.

Offline jongoff

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After some thought I realized that the answer to your original question “Are inflatable modules even necessary for private space stations?” is, self-evidently, yes.

Why? Because no other private party is attempting to create a space station of any kind. No other private party has spent significant money nor have they orbited one, let alone two, test space craft. No private party has talked NASA into testing a prototype on the ISS.

Why? Economics and vision. (I believe.)

Inflatable modules are necessary for private space stations because no one else is building any other sort of private space station.

“if there is a business case for private space stations, why these would be necessary?”

Because Bigelow Aerospace is the only one building private space stations and inflatables are what they believe will work. Presumably they know what they're doing.

I suspect that's not the answer you were looking for but it is the reality.

BEAM probably isn't necessary to BA's business plan but it certainly can't hurt and may provide a kick start to investment and customer orders.

I guess I'd find this line of reasoning more compelling if I thought Bigelow Aerospace's odds of succeeding were higher. They're definitely the only ones publicly working the problem, but that's no guarantee of success. Once again, I hope they're successful, but I've been hoping that for over a decade and a half. Personally, I wouldn't be surprised if some other party beat them to market at this point. Hopefully BEAM can turn things around for them as a company.

~Jon

Offline Norm Hartnett

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Yes BA really does need an Angel, someone to come along and buy a BA330 and loft it along with the manned flights and a utilization plan. However, until there are commercial manned flights there really isn't a market so it's unlikely there will be competitors.
“You can’t take a traditional approach and expect anything but the traditional results, which has been broken budgets and not fielding any flight hardware.” Mike Gold - Apollo, STS, CxP; those that don't learn from history are condemned to repeat it: SLS.

Offline Oli

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I am sceptical as well. An inflatible station means the entire hull must be flexible/expandle. I suspect that severly limits you  in the materials you can use and in the overall design. A non-inflatible station needs a rigid hull but you can fit it with whatever protection etc. you like.

So other than volume and potentially mass I only see disadvantages.

Btw, why not use composites for the hull instead of aluminium?
« Last Edit: 04/02/2015 06:08 am by Oli »

Offline cosmicvoid

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Because Bigelow Aerospace is the only one building private space stations and inflatables are what they believe will work. Presumably they know what they're doing.

One would hope they know what they're doing, but comments by BA ex-employees make me skeptical.  I'm not anti-BA; I hope they succeed.

I am sceptical as well. An inflatible station means the entire hull must be flexible/expandle. I suspect that severly limits you  in the materials you can use and in the overall design. A non-inflatible station needs a rigid hull but you can fit it with whatever protection etc. you like.

The rigidity of the inflatable is in the core/spine, which is not flexible.  The solid hull needs added protection, so I don't see its advantage.

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Btw, why not use composites for the hull instead of aluminium?

I'll take a guess here that composites are too brittle, and difficult to repair. And probably very expensive.
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Offline Oli

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The solid hull needs added protection, so I don't see its advantage.

Yes, but an inflatable might as well. If I understand correctly the Kevlar (or Kevlar-like) fabric in inflatables basically doubles as "structure" (in the sense that it keeps the entire thing from exploding), while on ISS modules for example it must be added as protection. However, ISS modules also have bumpers (aluminum sheets) placed at a standoff which causes incoming particles to disintegrate before they hit the inner wall. For deep space additional radiation shielding would be necessary, for example plastics, water tanks etc. The question is whether such additional protection could easily be designed to be flexible (as a fabric) such that it is expandable and if yes, how much more costly it would be.

I'll take a guess here that composites are too brittle, and difficult to repair. And probably very expensive.

They could be too brittle in the event of an impact. I do not agree on cost though, composite pressure tanks from what I know are cheaper than metal ones.

Offline Paul451

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For deep space additional radiation shielding would be necessary, for example plastics, water tanks etc. The question is whether such additional protection could easily be designed to be flexible (as a fabric) such that it is expandable and if yes, how much more costly it would be.

You're not sure if plastic and water can be flexible?  :o
 
But in general, you seem to be assuming that radiation and micrometeorite protection haven't been developed for inflatables yet. Bigelow's inflatables are made from the sort of materials that are already used to protect space suits and which have been added to ISS modules. They have been tested on Earth and in space.

ISS modules also have bumpers (aluminum sheets) placed at a standoff which causes incoming particles to disintegrate before they hit the inner wall.

Whipple shields. However, there are downsides. 1: The shield destroys itself when it is hit. You need to replace any section of shield that has been hit. I believe the practice now is to protect the Whipple shield with an external panel of multi-layer fabric shielding (Kevlar/Nextel/etc) which don't have to be replaced after every impact, leaving the Whipple shield as the last resort. (By protecting the Whipple from smaller impacts, you preserve its function for major impacts, while reducing maintenance.)

2: Whipple shields are fairly light, but the necessary gaps means they are bulky, they eat into your volume. Multi-layer fabric shielding is not quite as bulky, but importantly, in inflatable modules, you make up the volume by removing empty internal volume of the module during launch.

3: Whipple shields create radioactive particle showers when hit by high energy particles, effectively multiplying the radiation load on the astronauts. I believe the external fabric layers on ISS were intended to reduce this effect too.

Offline Paul451

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I'll take a guess here that composites are too brittle, and difficult to repair. And probably very expensive.
They could be too brittle in the event of an impact. I do not agree on cost though, composite pressure tanks from what I know are cheaper than metal ones.

They would be more expensive once designed to survive in space. Ie, once designed not to be brittle, not to degrade in a vacuum or monoatomic oxygen, or direct sunlight or sharp thermal cycling, etc.

Offline TrevorMonty

Bigelow plans to add radiation shielding by Velcro bladders of water attached to inside of wall. Given its large internal diameter, layering these shielding bladders shouldn't be an issue. As technology improves the shielding bladders can be changed for something better.

Offline Burninate

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Bigelow plans to add radiation shielding by Velcro bladders of water attached to inside of wall. Given its large internal diameter, layering these shielding bladders shouldn't be an issue. As technology improves the shielding bladders can be changed for something better.
Whole-hab shielding of this sort gets extraordinarily mass-intensive very quickly.  Water (and food, and equipment, and everything else) that has to be on the hab anyway, can of course be mounted on the walls for free.

We use these pools for short-term storage because water is a really good radiation shield. How good? Well, according to a report on the topic prepared for the DoE back in 1977, a layer of water 7 centimeters thick reduces the ionizing radiation (rays and particles) transmitted through it by half (the remainder is captured or moderated to non-ionizing energy levels, mainly heat).

A BA-330 has something on the order of 260m^3 of interior surface area.  7cm of water over the whole of the habitat is 70kg/m^2, bringing the total mass cost to 18.2 tons for a 50% reduction in solar radiation.

So effectively, to halve the radiation load you need to ~double habitat mass.  To reduce it by 75%, you need to ~triple habitat mass.  To reduce it by 95%, a 20 ton BA-330 becomes a 98 ton BA-302, accounting for the reduced volume: One ton of water for every four cubic meters.

The math isn't so extreme on larger habitats.  A BA-9000 has only about ten times as much surface area as a BA-330, and a 95% radiation reduction there can be accomplished with around 800 tons, or one ton of water for every 11 cubic meters.

In my opinion, for any habitat that has to move around, creative mounting of the chemical or nuclear-thermal propellant tanks, and thermal countermeasures to permit that, using semi-cryogenic fuel, will probably be the first really effective whole-hab radiation shielding.  Short of that, I think we'll see "safe rooms" established out of the existing interior water supply, where the crew will retreat only during solar radiation storms.  Packing the crew into a refrigerator-sized safe room for a few hours per mission doesn't cost much, design-wise, and doesn't pose extraordinary psychological issues for the crew in such a limited capacity.
« Last Edit: 04/03/2015 03:08 pm by Burninate »

Offline baldusi

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Plypropylene has a similar capability wrt radiation as water. You could layer it on the outside of an aluminum can and get the same effects. So, it's not like it's such a huge advantage.
The main issue I see for inflatable is outfitting. You have to spend a lot of crew time installing equipment and moving things around. And the configuration affects the radiation shielding, too. The ISS and such 4m al cans put all the equipment and ECLSS on the outside, which also acts as radiation barrier. The BA330 inflatable, puts all those things on the core, putting the crew closer to the walls, thus, only the inflatable walls act as radiation shield.
When you look at the SkyLab II trades on interior configuration, you find the same configuration as the BA-2100, i.e. three "floors". The big difference is that in an 8.4m aluminum can, all the equipment and ECLSS is already installed and routed on the comfortable gravity well of Earth's surface, while a BA-2100 would need a lot of ducting and installation. Things as silly as ventilation ducting, with the required power and data would eat a lot of crew time in installation. Is is worth the savings in mass if you have to spend an extra six months on orbit (or even more) doing simple installations?

Offline A_M_Swallow

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{snip}
When you look at the SkyLab II trades on interior configuration, you find the same configuration as the BA-2100, i.e. three "floors". The big difference is that in an 8.4m aluminum can, all the equipment and ECLSS is already installed and routed on the comfortable gravity well of Earth's surface, while a BA-2100 would need a lot of ducting and installation. Things as silly as ventilation ducting, with the required power and data would eat a lot of crew time in installation. Is is worth the savings in mass if you have to spend an extra six months on orbit (or even more) doing simple installations?

An outfitting time of several months definitely pushes towards have a spacestation to assemble the transfer vehicles.

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