Thoughts on hulls and their construction

[warwizard]

Ok fellow travellers this discussion is not tied to any particular ruleset,it's for general discussion of hulls.

As currently stated in multiple rulesets the standard hull is built up with a frame (internal or external) and plating.

A lesser used option is to use a found asteroidal body and carve out some portion of the asteroid for the volume required for the machinery.

As I found in another thread there are some objections to the use of a asteroid type hull, with house rules from larger sizes than required in the rules, to outright prohibition.

 

[warwizard]

The more general hull construction with a frame and plating has a number of assumptions that I'd like to examine.

Let's start with today's spacecraft. The hulls are of the stressed skin type wherin the plating is intended to carry most of the loads the craft will be subjected to, and are designed to only take large accelerations in one direction with transverse loads to be very limited. A saturn V rocket can pull some 7g's, but as little as 1/4 g applied at right angles to that may result in failure of the hull. It's just not stressed for 6 axis of thrust nore for high rates of rotation in any axis.

So we are assumming in the design sequenses that the thrust will be largley applied from a single point on the hull's surface, and we completly ignore any attitude control system, and no provision is made for off axis thrust and the structural bracing that off axis thrust would require.

 

[warwizard]

So what does a field based propulsion system do to this design paradgim?

Case in example would be an antigravity equiped small craft, wherin the anti gravity modules are distrubited many places on the skin of the craft. An additional thrust agency may be installed which would follow the normal paradgim, but your thrust provided by the antigravity is not located on a single point on the hull, so you would not need to add a structual factor for the accelerations available from the antigrav modules.

What is the effect of an inertial compensation system where the mass inside the hull does not "feel" the acceleration? Are these forces simurally foccussed on the distrubited nodes of the inertial compensation system? Does this break the single point of thrust concept for designing the internal bracing? Should you be able to build a bigger ship if you install g compensation, will it take less internal bracing?

 

[Dragoner]

From looking at the plans, Traveller starships are a semi-monocoque fuselage, with structural reinforcing bulkheads.

 

[DaveChase]

Space Crete

Using the concept of concrete but in space.

You could use something similar to concrete canvas
http://www.concretecanvas.co.uk/index.html


Or you could do the inflatable form that stays as part of the hull.
I like this idea as you can have a reflective or absorbing like hull (the inflatable material) and everything pre- wire, plumbed and outer airlocks in place.

This also would allow for some very custom designed ships that other ship yards might not be willing to attempt.

Pump in the crete which is made up of that useless junk that the miners can not sell and bonding agents. The interior walls can be of the same material or other.

The ship will have lots of mass and unless you honeycomb or build very solid interiors, the ship most likely will never be able to land on a gravity world.

(Of course this is not a solid true fact, it might be possible to make a very structurally sound crete ship that can handle multiply gravity landings. After all there are concrete canoes that are built and used every year.)

During battle, depending on what type of weapon damage you receive to the hull, you might automatically have a laser and missile dispersion field that travels with the ship.

The outer hull, (the inflatable mold) can be easily repaired by just slapping on a patch over the exposed area.

Just a basic concept of my idea of Space Crete built ships.

Dave Chase

 

[warwizard]

Thanks Dave, that sounds like it could be adapted to use a bit more temperature stable form (mold) and spray pressurized gas saturated liquid metal into the mold (under vaccuum conditions to create an expanded metalic foam hull shape) As you pointed out the metals would be the stuff for which there is no market that would bear the cost of transport, such as iron and nickel.
What would be the in game statistics of such a hull? The limitations and benefits and the cost?

Ok what about toughness and density per cubic meter?
If we have an Iron hull it's not very tough, could carbon be added to the molten metal to achieve steel, (or nickel steel) giving a slight bump to the toughness, perhaps, so we'll use the toughness of a hard steel (TNE or T4 or T5) and go by the mass we want per cubic meter if solid steel is toughness 2 and density 8, perhaps the expanded hard steel will be toughness .5 and density 2. this would have the effect of using 4 times the volume of the hull material in a standard hull in these rule sets, this could be applied to the rule sets that do not track this by consuming a percentage of the normally usable internal volume somewhere in the 2% to 4 % range I'd guess.
Benefits: Cost is very low, it does not take thousands of man hours to create a molded hull form, and the mold would be reused so you'd get the volume discount, standard drives can be mounted. by carefully controlling the process the bubble size could be controlled, perhaps in some areas creating a open cell foam for use in storing hydrogen... fuel tanks shattered? So what? put a patch on the hull the hydrogen's still here, well most of it any way.

Concrete can be quite remarkable stuff, if processed correctly you can create concrete springs. an ultrasonic vibration causes all the normal voids in the bulk material to be removed prior to the material setting, and it's these voids that serve as starting points for cracks.

 

[aramis]

From looking at the plans, Traveller starships are a semi-monocoque fuselage, with structural reinforcing bulkheads.

Agreed; tho' I'd hazard, based upon the much thicker outside lines on most plans, that the bulkheads are not really structural members, making them truly monocoque hulls.

TNE/T4 FF&S/FF&S2 hulls are NOT monocoque, but apparently frame designs which may be armored to become semi- or full- monocoque designs.

Asteroid Hulls - issues
My objections to asteroid hulls are primarily that the larger non-spheroidal asteroids appear to be rubble-piles, not monolithic chunks.

But note that many smaller asteroids (up to several dozen meters short axis) are monolithic (literally, "single-rock"), or more literally, solid chunks of either metal alloy or silicates... I'd put an UPPER limit on asteroid hulls, not a lower. The middle zone is the "no man's land" of neither collapsed to polylithic nor small enough to be routinely monolithic. If we say a 24x36x48 chunk as a larger monolithic sub-collapsing non-rubble-pile, that caps around 1551Td... Call it 2000Td for good measure... and the smallest self-rounding look to be in the 300m range, or about 321KTd...

Anything in between is likely to be rare. I'd happily allow larger asteroid belts to have up to even 5KTd monolithic chunks... but most of the bigger stuff is looking to be either ices or rubble piles real world.

Asteroid Hulls part 2: TANSIS Lives

The "cool reason" to have an asteroid hull is stealth. But since stealth goes out the window the moment IR telescopes are invented (ca TL 6), they're really only good for preventing TL 5 or lower societies from detecting you.

Other peoples neat ideas so far
So... polymerized fabric is cool. Especially DaveChase's inflated concrete form... Concrete is relatively cheap.

Just remember, tho': concrete can take years to cool. Especially when it can only radiate, not conduct, the heat away. And concrete has a lot of thermal storage capacity - a high specific heat - tho' not the highest known, and it is a mediocre thermoconductor. And most concrete releases heat as it sets. A lot of that gets trapped within.

IIRC, A meter thick concrete structure can take over a year to cool with air conduction... A friend's house, a poured concrete structure with up to 1m thick areas, has less than the normal snowcover 2 years on... He said it should be finished cooling by the end of summer next. (He's a construction foreman and contractor.)

 

[DaveChase]

Actual I was not figuring or counting on any metals. More the left over dust and debris that miners don't want. Metals will always have some market.

There might be some left over metals scattered in the material that was too time consuming for the cost of sale/profit, but not much.

I am also counting a bit on higher technology than we have right now to make Space Crete work well. Concrete will work if you can keep it warm enough to dry. But make it too thick and it will take decades or longer to cure. (Hoover Dam is a good example of this.)

The only major down fall to a solid 'concrete' ship under combat is no flex to such a structure. Get some massive explosions close but not on top of the ship and it could stress the hull like an earth quake does a solid concrete home. Sure the hull/building is still there, but it will need some repairs. Where a regular hull/building would be demolished.

Hence the outer skin and possibly the inner one to would be an extra layer of sealant to help keep the air in. The inflatable hull skin that I am thinking of is a double layer of the shape of the ship and the crete is forced into that void between the outer and inner layers.

Dave Chase

 

[Whipsnade]

The only major down fall to a solid 'concrete' ship under combat is no flex to such a structure. Get some massive explosions close but not on top of the ship and it could stress the hull like an earth quake does a solid concrete home.

Bingo.

The problem with the current HG2 planetoid hull model is two-fold. First, the hulls are too cheap. They're too easily found in too many convenient sizes which can be too easily modified into hulls.

The second part of the problem is one of armor. Planetoid hulls provide too many armor levels too cheaply.

I'm not saying that starship hulls cannot be made out of chunks of planetoids. I am saying that such hulls will not be "essentially free", will not only need a 100Cr/dTon transport, will not require only a 1000Cr/dTon tunneling fee to make them fit for use, and will not provide automatic armor levels depending on how much of the chunk is left intact.

 

[warwizard]

Ceramics can get past the whole tap it with a hammer and it shatters assumption. Have a read here

 

[Enoki]

I would assume that the standard hull design (armor 40) is some sort of composite armor much like is used on AFV today. The materials probably would be tougher than plain steel as more choices would be available. By using several layers of different materials you greatly increase the probability that some object won't make it through the hull.
At higher tech levels the materials might have been increased in density over their naturally occuring ones through various gravitational and pressure manufacturing processes.
I could see metals using powder technologies to control crystal size and give very uniform small crystals that are extremely tough. I would think that triple alloy steels (where steel is used, if it is) would be the norm.... Chrome, vanadium, molybednyum, nickel, cobalt, are all possible additives.
I would also think that as tech levels advance the quality control process would improve where the materials have zero flaws, zero impurities, etc., in them making them stronger and less succeptable to things like corrosion.

Using a meteor for a hull would give up many of these qualities so a constructor would have to substitute brute force for subtitlety.

 

[Dragoner]

Structual concrete is generally sleeved in steel to prevent shattering in shear.

Agreed; tho' I'd hazard, based upon the much thicker outside lines on most plans, that the bulkheads are not really structural members, making them truly monocoque hulls.

Small ships like the Pinnace look like monocoque construction, the Plankwell looks like an interior frame. Problem with a structural skin only design like a monocoque, is it isn't very strong, the pictures of crashed ships generally shows them intact.

 

[far-trader]

...They're too easily found in too many convenient sizes which can be too easily modified into hulls.

Yes! This is one thing I long wanted to change/fix/houserule. Some randomness in the size you find. Say for example you want a 400ton hull, you go out asteroid shopping and find a suitable candidate after a week that is 283tons before working. Too small. Another week of looking and you find one that is 821tons before working. So you could trim that one down to your 400tons (at the basic tunnelling cost*) and then begin the real work, or look for one closer to what you want.

Also, the nature of "found" rocks for hulls should mean all the components cost more to fit to the unusual layout, or you lose even more waste space.

I also think the waste space requirements are too low. I once deckplanned a buffered rock and the amount of material left was woefully thin for a skin over the whole volume. It looked barely thicker than what I'd make a metal hull.

 

[DaveChase]

Structual concrete is generally sleeved in steel to prevent shattering in shear.





Small ships like the Pinnace look like monocoque construction, the Plankwell looks like an interior frame. Problem with a structural skin only design like a monocoque, is it isn't very strong, the pictures of crashed ships generally shows them intact.

As Concrete tech advances, it may no longer be steel or other metal. It may very well be a fiber mesh.

There are several fiber mesh mixtures on the market now that help reduce or eliminate the need for structure metal mesh or rods in the concrete.

The fiber mesh also helps reduce the number of micro cracks which can lead to larger cracks or seepage issuses.

Note: I am not in any way claiming that Space Crete would replace or be better than what is currently listed in any Traveller Tech for hulls. I am just offering an alternative to the common hull.

This Space Crete might be less expensive than a standard hull, and could be put together quicker and allow a more custom type hull. Then it would also be more massive in mass versus a standard hull so it would take more power to get it moving or stopping. It could also be done in places that don't have a shipyard. But it would take prep time for local materials and certain equipment like pumps and slurry (Mixing) machines to make the crete.

Like I said just some thoughts on an alternative type hull.

Dave Chase

 

[aramis]

Structual concrete is generally sleeved in steel to prevent shattering in shear.





Small ships like the Pinnace look like monocoque construction, the Plankwell looks like an interior frame. Problem with a structural skin only design like a monocoque, is it isn't very strong, the pictures of crashed ships generally shows them intact.

Crashed Cessnas often look terrifically intact until you get to the right angle. And those are semi-monococque.

Some larger monocoque aircraft can look pretty much intact until you get close, as well. It depends a lot on whether or not it was able to flare off the speed prior to impact.

 

[Whipsnade]

Note: I am not in any way claiming that Space Crete would replace or be better than what is currently listed in any Traveller Tech for hulls. I am just offering an alternative to the common hull.

This Space Crete might be less expensive than a standard hull, and could be put together quicker and allow a more custom type hull. Then it would also be more massive in mass versus a standard hull so it would take more power to get it moving or stopping. It could also be done in places that don't have a shipyard. But it would take prep time for local materials and certain equipment like pumps and slurry (Mixing) machines to make the crete.

All excellent ideas and all very different from HG2's "find a rock, tunnel a rock, fly a rock" model.

 

[Enoki]

Given that space is generally cold, this might be a cheap alternative too:

http://en.wikipedia.org/wiki/Pykrete

 

[aramis]

Given that space is generally cold, this might be a cheap alternative too:

http://en.wikipedia.org/wiki/Pykrete

There's a reason that stuff isn't used much - anyplace warm enough to be comfortable for humans is too warm for long term use of pykrete. And radiative cooling of it is going to make it less than practical as an emergency shielding material.

Still, it has some wonderful practical applications for cold worlds... building barriers, building rafts on open ocean....

 

[Enoki]

There's a reason that stuff isn't used much - anyplace warm enough to be comfortable for humans is too warm for long term use of pykrete. And radiative cooling of it is going to make it less than practical as an emergency shielding material.

Still, it has some wonderful practical applications for cold worlds... building barriers, building rafts on open ocean....

As a hull application it would work. Simply build a inner hull as a dewar flask. The hull stays cold the humans stay toasty..... At least in space it would work... just don't go too close to the star......

 

[warwizard]

Proposed house rule:

Ok so let's call this construction method a cast hull rather than a constructed or a tunnelled one.

A mold is produced defining the size and shape of the finished hull. This method is usable for unstreamlined and partially streamlined hulls, (and some airframe/ fully streamlined configurations at a higher cost)

forms are placed in the interiour to establish and define the interiour spaces of the finished ship. plumbing and radiator heat conduits are placed. If needed lanthanum grids are placed, very large items like power plants, maneuver, and jump drives may be prepositioned inside the interiour forms.

The hull material is delivered into the space of the hull in a liquid or slurry form, and converted to a solid through cooling (liquid metal, polymer reinforced water or other matrix materials of advanced composite materials) or a chemical reaction (cement), or by applying heat, (ceramics).

Game effects: Construction time is reduced, construction cost is decreased
Hull may have defects such as brittleness, eroding/melting, or reduced toughness per volume.

I invite others to propose the in game effects for their rule set of choice with specific values for the different proposed materials and to show improvements as the TL increases.