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#26 2019-07-07 15:27:03

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,959

Re: Redux of ISS If we could

Robert,

In that case, you already know who to talk to.

The simple solution to a more robust design is to add more mass.  That's also pretty much the only solution we know of.  We know how to make a given mass of materials stiffer yet lighter and therefore less likely to deform under load, with proper part geometry or use stronger materials for a given mass, but that's as far as that goes.  That's still not actually "stronger" than "more mass" if both parts had proper geometry, only stronger for a given mass.

The most promising of the "stronger materials for a given mass" seems to be CNT.  Nothing else we actually know how to make is stronger for a given mass of material, and the nearest carbon fiber competitor isn't even close.  No metal, nor metal alloy, nor ceramic metal alloy, even comes close.  So, there you go.  We have known how to make aerospace structures more durable for quite some time now.  We add more mass or we use stronger materials for a given mass.  We also take the operational temperature and other environmental factors into account, such as radiation / pressure / exposure to various chemicals / etc.  There's no other form of "engineering magic" to be had.

A good finite element analysis will tell you, roughly, how strong is "strong enough for the specified use, and no stronger".  Thereafter, it's off to perform load cycle testing (structural testing to destruction) to validate the FEA modeling results.  If the simulations are an accurate depiction of reality, then test results will mimic the simulations.  If not, then it's time to adjust the FEA code to bring simulation into agreement with the physical world.  This is typically not a "fast and cheap" process.  If that sort of work is "fast and cheap", then in all probability the quality of the work is questionable at best.  I wouldn't bet my own life on substandard work, nor anyone else's life.  I most certainly wouldn't bet the lives of irreplaceable NASA astronauts on a FEA simulation done in a single afternoon.

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#27 2019-07-08 08:06:56

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,652
Website

Re: Redux of ISS If we could

Re:  metal fatigue --  I see from today's emailing of AIAA's Daily Launch newsletter that early,  older models of the Airbus A380 are under an inspection order for rear wing spar cracks between ribs 35 and 49.  That would obtain if either (1) they cut too close to a fuzzy statistical design limit for allowable stress,  or (2) they didn't fully understand all the loads this part would see,  or (3) those models have already exceeded their design number of cycled loads (also a fuzzy statistical limit. 

Re:  inflatable modules from Bigelow  --  These have a hard core upon which the multi-layered inflatable is attached.  The inner layer or layers is a gas-tight polymeric material sort of like a rubber,  and is the "balloon" vessel that holds pressure.  The rest of the layers are flexible fabrics that provide multiple functions:  (1) mechanical protection,  (2) thermal insulation,  and (3) radiation shielding.  That mechanical protection includes a significant degree of meteroid impact protection. 

For the simple BEAM module on ISS,  this was a one-off design with protection layers only half a meter thick and no hard core at all,  intended to provide the same radiation protection or better,  than the hard ISS modules provide.  Bigelow's actual module designs are more like the B330 module you can explore on their website. It has a full meter wall thickness of the 3 protection functions,  twice as good as what NASA is evaluating at ISS. 

That's not good enough for protecting against a solar flare outside of LEO,  but it is good enough to reduce GCR exposure significantly. 

Don't kid yourself about impact damage protections.  There may be more meteroids outside LEO,  but there's more space debris in LEO.  An impactor is an impactor is an impactor,  whether a paint flake or a grain of rock.   You still need the protection,  either way.

GW

Last edited by GW Johnson (2019-07-08 08:08:36)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#28 2019-07-08 18:33:11

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,173

Re: Redux of ISS If we could

While its an inflateable the facts taht you need to shelter the unit while launching and then add addition materials for use beyond LEO for use to moon or mars or anywhere else. What they give you is expandible space from the launched volume but is there any thing else that is a plus or a minus from this type of module?
Bigelow inflateable images

Nodes for the ability to get more than 2 connected to a common location is a drawback to regular modules and the inflateables.

Bigelow.jpg

So we are going down the path of having different size parts which lead to something like this

bigelowmodules.png

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#29 2019-07-09 00:21:08

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,794
Website

Re: Redux of ISS If we could

Bigelow inflatables are based on TransHab. They have a firm polymer layer to break up stony micrometeoroids, then an open cell foam spacer, then ballistic Kevlar cloth woven in the same pattern as personal body armour. This entire sandwich of material is repeated 2 more times for a total of 3. The fabric module is said to be safer than a metal hull, but that does not take wear or fatigue into account. If a tiny micrometeoroid strikes a metal hull, it does nothing. When a micrometeoroid strikes the fabric, it cuts a hole. The way Kevlar fabric works, as a bullet or micrometeorite strikes, the fabric forces it to spin. Then next layer of Kevlar fabric forces it to spin in the opposite direction. The next in the opposite direction again. Each time bullet spin is changed, it loses energy. However, as the fabric forces the bullet to spin, the bullet tears through the fabric. These wholes accumulate. How many strikes from micrometeoroids or debris before the Kevlar jacket is compromised to the point it's useless?

Single-strike the fabric inflatable may be safer than a metal module. However, how does it stand up to repeated strikes? What is long-term durability?

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#30 2019-07-09 07:57:25

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,959

Re: Redux of ISS If we could

Robert,

Have you seen how many times you can shoot a Kevlar vest before it fails to stop subsequent projectiles?

The number of repeated hits that the newer vests can take, even within the same area, is pretty impressive.  Anyway, repeated hits to different parts of the module probably won't cause any immediate structural failures.  Multiple hits to the same area would be more of a concern.  For an Aluminum module of the same weight and volume, the projectiles would pass right through with minimal resistance.  If the fabric used was a woven CNT, then it would be many times stronger than the best aramid fibers for the same weight.  Woven MWCNT roughly the same thickness as a piece of construction paper, but less weight than the paper, can stop handgun bullets.  No similar mass of aramid or metal has any hope of stopping a bullet.  That's why I keep harping on the use of stronger yet lighter materials.  The benefits are very real.

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#31 2019-07-09 09:25:33

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,794
Website

Re: Redux of ISS If we could

kbd512,

The only multi-strike data I've seen is from a unique vest called "Dragon Skin". It consists of Kevlar over multiple overlapping disks of ceramic. Kevlar without any hard reinforcement can stop low calibre bullets, but not high calibre. The solution is a ceramic plate inserted behind the Kevlar. Body armour Level II can stop a bullet from a 9mm handgun, Level IIIa can stop a .44 Magnum bullet, Level III can stop a .223 bullet from an M16 or AR15, Level IV is required to stop a .30 calibre or .338 Lapua Magnum or .50 Browning. However, the ceramic plate is broken by impact of the bullet. If a second bullet hits the same point of the vest, it will go through because the ceramic plate (hard armour) is broken. Dragon Skin tries to fix this, instead of a single large chest plate and a single large back plate, Dragon Skin uses multiple overlapping disks. Still, a high calibre hit will break a ceramic disk, if a second bullet hits close enough that it hits the vest where the disk was broken by the first bullet, then the second bullet penetrates. With large plates, the fracture is multiple lines that cover the entire surface of the plate. Although sections of the large plate can still be effective, if a second bullet hits very close to the first bullet where the plate is broken into multiple tiny bits, or anywhere along one of the fracture lines, the second bullet will penetrate.

Oh wait! Now we're talking hard plate behind fabric. ISS modules today have thermal blankets made of an outer layer of 400 denier Goretex fabric and inner layers of multi-layer insulation, same as the white EMU spacesuits.

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#32 2019-07-09 10:12:42

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,069

Re: Redux of ISS If we could

For kbd512 and RobertDyck .... thank you for this informative exchange .... I have no interest in getting into the middle of it.

However, re #31, I am wondering if "intelligent" / "smart" ceramic plates might be worth considering for deep space missions and for long term facilities in LEO.

These would contain a chip (similar to an animal tracking microchip) which would report on ceramic plate condition when interrogated by a robot inspector making its periodic rounds. Damaged plates could then be replaced, assuming the fabric holding the plates is designed to support replacement.

For RobertDyck .... If you were thinking of leading an exercise to design a 100 year habitat, I'd like to offer my encouragement.  Leadership (among other things) involves taking fire from critics, and I can see in the history of this forum, that you've been doing that for some time.

The consumers of your habitat design (should it come to pass) are alive and in school right now, here on Earth.

(th)

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#33 2019-07-09 17:18:42

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,173

Re: Redux of ISS If we could

The ISS currently has whipple shielding blankets which are kevlar cloth with thin aluminum plates sandwiched in between which can be replaced as needed. So what else can we do to make for a better station to everywhere?

The Radiation Challenge
https://www.nasa.gov/pdf/284273main_Rad … S_Mod1.pdf

STRUCTURAL MICROMETEOROID AND RADIATION SHIELDING FOR INTERPLANETARY SPACECRAFT
https://pdfs.semanticscholar.org/8f24/7 … 603686.pdf

Shielding Strategies for Human Space Exploration
https://www.dartmouth.edu/~sshepherd/re … cp3360.pdf

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#34 2019-07-09 19:55:00

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,959

Re: Redux of ISS If we could

Robert,

Every plate or vest rated to stop multiple hits must do so to pass NIJ testing.  If not, then it's not NIJ certified.  It may or may not stop two or more rounds that go through the exact same hole, but nothing is indestructible.  Suffice to say that pretty much any multi-hit rated plate or vest will perform as advertised.  Some are pretty remarkable, others somewhat less so.

Even a ceramic ballistic material doesn't necessarily equate to a one-hit wonder:

ATS Amor - Type IV Hard Armor Plate Demo

That's an incredible number of AP rounds for a single plate to take, none of which penetrated.  I thought for sure that that many M855's through the same hole would penetrate, but they didn't.  Mind you, anyone wearing that plate may have died anyway from blunt force trauma, in my opinion not a good way to go, but at least they wouldn't be perforated.

I suppose some combination of ceramic panels and fabrics could be added to a spacecraft's hull, but not without a substantial weight penalty.  As light as the Aluminum is, it needs to be even lighter, else the rockets need to become more fuel efficient.  I believe the aramid fabrics have already been tested with small projectiles fired at orbital velocity.  They fared far better than Aluminum.  Anything with enough velocity behind it will penetrate.  That's just simple physics and not much else.

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#35 2019-07-09 21:26:48

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,794
Website

Re: Redux of ISS If we could

Impressive. I haven't seen any video or read anything of an armour plate that could take that many hits without failure. The caveat is I agree with you re blunt force trauma.

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#36 2019-07-12 15:18:35

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,652
Website

Re: Redux of ISS If we could

I'm no expert on ballistic protection,  but there seems to me to be very difference (other than thickness) between NASA's blankets on the ISS modules and Bigelow's multiple layers surrounding their inflatables. 

Both seem to be layer-space-layer meteor bumpers of the type I first saw proposed in the 1950's.  Testing since then shows they work.  I would think that meteoroids (or debris) striking the exact same spot would be wildly improbable,  so the useful lifetime should be quite long.

What I like about Bigelow's approach is that it also provides a meter of low molecular weight radiation shielding,  which seems to be fairly effective reducing GCR exposure.  That's not to say that ceramic platelets cannot be added,  but the resulting armor would be less flexible,  and therefore less amenable for Bigelow's brand of inflatable compressed storage. 

In the case of the inflatable (or a hard shell module) protected by an armor blanket, prudence and ethics simply demand that you plan on the inner pressure layer getting penetrated now and then.  What that means is that you must have easy access to the entire pressure layer (or shell) to make those patch repairs. 

You CANNOT mount equipment or supplies on that pressure wall,  much as you want to.   When the emergency happens,  you do not have time to move stuff to get access. Most of what time you have will be eaten up just finding the hole.

Why I like Bigelow's approach is that access to the pressure layer is exactly what their core-based design provides (B-330,  not BEAM).  The equipment is all stashed in an inner hard core structure inside the pressure layer and armor/shield layers that are inflatable.  That means the inner pressure layer wall is bare and completely accessible,  once the module is inflated and put into service. 

Because of the meter-thick layering,  there's a low probability of getting punctured,  but if it happens (and eventually it will),  you can immediately and easily find the hole and patch it.  Patching is easier done from the pressure side than the vacuum side,  too.

These are issues no one,  not even Bigelow,  is talking about.  But for long term reliable service in space with crew,  these are very critical issues.  I have always found it disturbing that no one talks about this. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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