Kevlar in Spacecraft

[Northstar1989]

Reading about THIS scientific publication, and a related Space.com news article, on The Mars Society page on Facebook, I was inspired by the idea of greater use of Kevlar in spacecraft...

https://www.nature.com/articles/s41598-017-01707-2

Basically, pound-for-pound, Kevlar is just as effective as Polyethylene as radiation-shielding in space (and MANY times more effective than Aluminum).  It's also denser (Kevlar has a density of about 1.44 grams/cm^3, vs. a maximum density of about 0.975 grams/cm^3 for Polyethylene)- meaning that a tile providing the same level of protection (measured in grams/cm^2) would also be thinner:

https://www.ptonline.com/columns/density-molecular-weight-in-polyethylene

http://www.dupont.com/products-and-services/fabrics-fibers-nonwovens/fibers/articles/kevlar-properties.html

But more interesting, Kevlar is also STRONGER than Aluminum.  Looking at two of the most important parameters describing strength (Tensile Strength, and Yield Strength) it is substantially stronger:

Kevlar

Tensile Strength: 3620 MPa

Yield Strength: 898.5 Mpa*m³/kg

http://www.tsgc.utexas.edu/tadp/1996/reports/tech/material2.html

https://en.m.wikipedia.org/wiki/Kevlar

Temper 6061 Aluminum

Tensile Strength: 290 MPa

Yield Strength: 240 MPa

https://en.m.wikipedia.org/wiki/6061_aluminium_alloy#Standards

7068 Aluminum Alloy

Tensile Strength: 710 MPa

Yield Strength: 683 MPa

https://en.m.wikipedia.org/wiki/7068_aluminium_alloy

 

7068 Aluminum Alloy is basically one of the strongest aluminum alloys that sees any actual commercial use, and is currently being considered as an UPGRADE for many spacecraft designs (weaker, but more workable alloys are currently used).  It currently sees its greatest use in military ammunition.

6061 is a relatively strong, basic form of extruded Aluminum, which sees many commercial uses.

------

My basic idea is this: since Kevlar is both stronger (pound-for-pound) and better at radiation-shielding than Aluminum, why not make greater use of it in spacecraft?  Particularly, why not work it into the structural elements of more spacecraft?

 

Regards,

Northstar

Edited November 18, 2018 by Northstar1989

[Bill Phil]

Compressive strength I'd wager...

[Xd the great]

How does kevlar fare in the extreme heat and cold of space?

[kerbiloid]

Spoiler

 An inflatable spacecraft.

 

Afaik while kevlar is strong against a bullet, it's still weak against a knife due to its fiber structure.
Can kevlar hold the gas pressure?

P.S.
Imho the radiation shielding should be provided by geometry, not materials.

Say, you have to put 25 g/cm² of passive rad-protection.
You can either launch, say, 2 t of kevlar instead of, say, 5 t of aluminium, or hide your cabin between the tanks and the cargo (like in TKS, he-he)

Edited November 3, 2018 by kerbiloid

[Gargamel]

3 hours ago, Northstar1989 said:

But more interesting, Kevlar is also STRONGER than Aluminum.

Take a sheet of Kevlar and a sheet of normal kitchen grade alimunum foil,   Slowly press a needle against it.   Which has more strength?  The foil of course, because Kevlar is a fabric that is woven, and the needle will pass through the kevlar as if it isn't there at all.     

Kevlar is made in threads.  I've worn them as armor, and used them in my climbing ropes.   It does have very strong tensile strength, but for it to work on a spacecraft, it would be the same as knitting a hat for it.   And I want a material that is more protective for the same volume and less dense, not more dense. 

3 minutes ago, kerbiloid said:

Can kevlar hold the gas pressure?

Woven like a net to help contain forces on a pressure hull, it would do just fine, as it is very strong.   But given the differences of pressure in space are usually less than 1 atm, most craft don't need to withstand a large pressure difference. 

Edited November 3, 2018 by Gargamel

[satnet]

18 minutes ago, Xd the great said:

How does kevlar fare in the extreme heat and cold of space?

Based on DuPont's technical report it actually handles both extreme heat and cold very well. According to their site it does see some applications in space, though it isn't a long list. It is susceptible to degradation under UV light and according to the Texas space grant consortium link provided in the original post it tends to sublimate in the vacuum of space. It also tends to absorb humidity and without sealant would let it evaporate into space. It is worth pointing out that Bigelow's inflatable habitats are based on Vectran, which is very similar to Kevlar (it is actually twice as strong). There probably are more than a few applications where it would be a good fit, but it doesn't seem to have found its niche in space just yet.

[kerbiloid]

6 minutes ago, Gargamel said:

Woven like a net to help contain forces on a pressure hull, it would do just fine, as it is very strong. 

So, instead of a simple aluminium waffle envelope made out of single sheet of aluminium, they should make a composition of foil, net, and glue.

Edited November 3, 2018 by kerbiloid

[Gargamel]

Just now, kerbiloid said:

they should make a composition of foil, net, and glue

Well, I guess, but without some numbers, that seems a lot heavier....

4 minutes ago, satnet said:

It is susceptible to degradation under UV light

Ohhh... Forgot about this...   We had to retire some of our ropes after a couple years of use just from this factor alone.   Not worth risking our life to something that has been exposed to sunlight for a long period of time..... of wait......

[YNM]

TBH I could see a spacecraft being made from such resin composite materials are covered in further things like aluminized mylar or somesuch. After all, punctures in space are almost always bullet-like rather than knive-like.

I'd say that if we give the inflatable modules a go that's primary usage for kevlar.

Edited November 3, 2018 by YNM

[kerbiloid]

1 hour ago, YNM said:

punctures in space are almost always bullet-like rather than knive-like

That was not about punctures.
As kevlar is much stronger than aluminium, and a kevlar envelope could be made much thinner, could such thin but fibrous envelope hold proper amounts of gas for a spaceflight duration.
Or to make it enough hermetic, it should be made even thicker and heavier.

Metallized plastic balloons didn't require atmospheric pressure inside.

Another point: you can attach things directly to the aluminium waffle envelope. Unlikely to kevlar.

Spoiler

Look, kevlar is just like Kerbals, it starts with "Ke-" !

 

Edited November 3, 2018 by kerbiloid

[YNM]

27 minutes ago, kerbiloid said:

you can attach things directly to the aluminium waffle envelope. Unlikely to kevlar.

Would stick to the resin though.

[kerbiloid]

1 minute ago, YNM said:

Would stick to the resin though.

Resin tanks to resin hull.

[YNM]

10 minutes ago, kerbiloid said:

Resin tanks to resin hull.

Yup. Sticks like glue !

[kerbiloid]

8 minutes ago, YNM said:

Yup. Sticks like glue !

A Bubbly Bubbly ship. 
A handful of sticky slime and a balloon with compressed air. Blow any shape you wish, they deflate and blow another one.

[Northstar1989]

I think some people here are under a false impression- that the primary force on a spacecraft to be resisted is the internal pressure of the fuel tanks.

It's not.  At least not on high-thrust chemical rockets, or any stage launched atop one (electric thruster-propelled spacecraft built in space would be an entirely different story, for instance...)

The main force the spacecraft have to contend with is that of their own THRUST: two, maybe three g's of force translating up the entire z-axis of the spacecraft from engines all the way up to the nose.

The forces involved are greater than those from the fuel pressing out on the pressure vessels (an interesting aside: the thickness of spherical pressure vessel laws increases in direct proportion to their volume, due to the Square-Cube Law for surface area vs. volume, and the linear relationship between pressure vessel mass and volume.  Larger tanks require thicker walls.  This is relevant to a few points raised in earlier posts.. ) at many point in the rocket, and so many rockets (especially large, tall ones: *cough* BFR *cough*) require extra structural reinforcement beyond the strength required to contain the internal pressure at many points along their length...

---

It is the external shells of large spacecraft, that overlay the pressure vessels and have no direct role in contacting the gasses, that I thought Kevlar (or better yet, Vectran) would be useful for.

Structural elements (the use I quite clearly emphasized in the OP: *not* use in strengthening the pressure vessels, which carbon fiber overwraps are actually more appropriate for...), which could, by the way, easily be overlayed with an extremely thin metallic outer coating to reflect UV away from the polymers beneath...

---

On Polymers and Ceramics:

- Further reading indicates that composites made using spun polymers such as Kevlar are exceedingly strong in tension, but very weak in compression.

- By contrast, certain ceramics are exceedingly strong in compression (far stronger, pound-for-pound, than Aluminum: which explains why there has already been substantial research into greater use of ceramics, and ceramic-based composites in spacecraft...  https://www.space.com/31516-3d-printed-ceramics-next-gen-spaceships.html   https://sbir.nasa.gov/content/ceramic-matrix-composites-spacecraft-propulsion).

- Appropriate use of polymers such as Kevlar where tensile forces dominate, and ceramics in places where compression is king, seems to be the key to next-generation, lighter-weight spacecraft design...  Indeed a lot of NASA research appears to be focused in precisely this direction.

---

In short, further reading indicates that what I was suggesting... has already been considered by much smarter people than myself, and indeed is actually precisely where spacecraft design is headed (although there seems to be more focus on Carbon Fiber than on Kevlar, as it is potentially even stronger: although far less capable of shielding crews and components from radiation...)

[kerbiloid]

1 hour ago, Northstar1989 said:

The main force the spacecraft have to contend with is that of their own THRUST: two, maybe three g's of force translating up the entire z-axis of the spacecraft from engines all the way up to the nose.

That's only for the first several minutes, when the ship can be deflated and the crew can hold the breath.

In orbit accelerations are < 0.1 g.

1 hour ago, Northstar1989 said:

Larger tanks require thicker walls.

But usually they are made of standard sheets, so are overweighted.

P.S.
Btw we should use an inflatable rocket (like Atlas) for an inflatable ship.

Spoiler

 

Edited November 18, 2018 by kerbiloid

[DDE]

Atlas was inflatable, AFAIK the R-7 uses tension loads on the center stagewhen the boosters are attached (hence the fancy sep sequence), but mainly spacecraft are built to survive compression loads. That's where metal is nogh-unbeatable. The only option for a non-metal hull is to depart from the monocoque design. Question is, would lightweight hull plus the structural frame weight less or more?

[4472TJ]

On 11/3/2018 at 2:10 AM, Northstar1989 said:

My basic idea is this: since Kevlar is both stronger (pound-for-pound) and better at radiation-shielding than Aluminum, why not make greater use of it in spacecraft?  Particularly, why not work it into the structural elements of more spacecraft?

Problem, Kevlar is more like a kind of putty than a solid form (correct me if I'm wrong). The problem there is obvious if you were to use it for a structural element. If you are trying to mean that you could use it in the ISS for radiation prevention that could be a possibility but the problem with liquids in space is that they like to clump together so if you had a hull like this:

(Kevlar(inside)Kevlar) 

After some time it would become, 

(Empty "space"(inside)Kevlar ×2) 

And for an astronaut that's not so good as it is letting in the radiation still.

[DDE]

5 hours ago, 4472TJ said:

Problem, Kevlar is more like a kind of putty than a solid form (correct me if I'm wrong).

Corrected.

Blankets of ‘raw’ SVM fibre, similar enough.

[wumpus]

Long, long ago I worked for a company working with scaled composites to build drones [a novel unmanned aircraft, not some helicopter variant, although it could take off and land in a *very* small runway] (sometime between the first and second wars in Iraq.  Unfortunately a major partner was a French military company and it didn't go anywhere).  Anyway, I was shown one of the early prototypes that was made out of Kevlar.  It had survived hitting a tree.  Kevlar might not be officially "strong", but it is very, very tough.  It also took far too long to cut and fabricate and they went back to fiberglass.

Note that the link below appears to be in Russian (or at least other Cyrillic using language), but the picture and untranslated parts appear to match.

[snip]

Edited November 19, 2018 by Vanamonde

[Vanamonde]

@wumpus, I'm sorry but that site is triggering some forum member's malware protections, so we've removed it. Maybe find a more secure source? 

[wumpus]

11 hours ago, Vanamonde said:

@wumpus, I'm sorry but that site is triggering some forum member's malware protections, so we've removed it. Maybe find a more secure source? 

Try this: https://en.wikipedia.org/wiki/Freewing_Scorpion

(note that specs refer to the larger craft built by Scaled in the Mohave, the smaller one was being built in Maryland).

http://stargazer2006.online.fr/unmanned/pages/scorpion.htm

(apparently the key was to remove both Scorpion and Scaled and stick with freewing and Rutan for searchterms).

[KG3]

EVERY time I've ever bought bicycle tires made out of Kevlar I've been told "it's twice as strong as the material in the regular tires".  But it seems like they use 1/5 the amount of material in the regular tires to "make them even lighter".  These tires have always disappointed me because they wear out twice as fast and get 5 times the punctures as the regular tires.  

[4472TJ]

22 hours ago, DDE said:

Corrected.

Blankets of ‘raw’ SVM fibre, similar enough.

Now the possibility is much more clear, the new(ish) blow up module on the ISS was mode of very thick layers of lots of material and this looks quite similar to the sort of stuff used in space suits and since a spacesuit is just a small spacecraft filled with air, like the module I mentioned, it could in theory work. One problem though is its ability to make an airtight seal (adding weight and costing) and its capability to endure heat from the sun and the shaded of the earth, and lots of materials don't like heating up and cooling down so rapidly (take a blacksmith working with metal, they do not want to cool the metal down too quickly and let it ruin their work) and this may be a reason for it not being used.

[wumpus]

6 hours ago, KG3 said:

EVERY time I've ever bought bicycle tires made out of Kevlar I've been told "it's twice as strong as the material in the regular tires".  But it seems like they use 1/5 the amount of material in the regular tires to "make them even lighter".  These tires have always disappointed me because they wear out twice as fast and get 5 times the punctures as the regular tires.  

if 700mm is the diameter, then you are dealing with more than 2m of tire with a moment of inertia based on a .35m radius (considerably bigger than most car tires).  So weight certainly matters.  But wearing out 5 times faster might not justify that.  But if there is one thing on the whole bike you want light, it is the tires (of course, it defeats all the benefit of lightness when you have a flat).