The best shape for Massive ships

[Crossroads Inc.]

So in the world of SciFi, there are a lot of BIG ships. The DS being one of the best examples. But when we get into just how exactly to MOVE really big ships, thing can get a bit murkey.

Now one would think for ships, say over 100km in diameter, that a sphere is the best way to go. But with a ship that big, what is the best way to put engines? one of the few examples we have is Fortress Geiersberg From "Legend of the galactic heros" Which had a ring of engines all the way around it. However as also shown in the show, this can be very unstable if only a few engines are destroyed.

So the question is put forth, if you have a ship over 100km, what is the best shape to make it if you wish to move it like a normal starship?

[Imperial528]

In terms of moving it I would say some sort of elongated sphere, with the profile of an oval. That way, it is strongest in the direction of primary thrust, and the curved shape should give it enough sheer strength to stand turning. That is, if you want it to be maneuverable and fast.
If you're going to go with a sphere, I'd suggest 6 clusters of engines, two clusters per axis so to have manageable thrust and counter-thrust. Each cluster would have engines whose direction of thrust is aligned with the axis and facing out from the origin, and they would also have engines whose thrust is perpendicular to the axis of that cluster, to allow for rolling and linear movements. It would provide more maneuverability than the first example, but you would be limited as far as speed goes relative to the first setup, although it would be much more stable and more able to handle the stress on itself.

[Elheru Aran]

I actually always did enjoy the Executor's proportions...

A sphere works well enough, but it's going to require a LOT of material to build because of its great volume, as does a cube. A more or less flat plane like the Executor, on the other hand, means you can create 4 or 5 ships with the same amount of material that you could use for a sphere of the same width/diameter.

And you also have to consider the function of the ship as well. Does it require a lot of interior space, does it need optimal weapons distribution, will it need thick reactor shielding, etc, etc... A sphere works well for some purposes but for others some shapes might work better.

[Ellindsey]

Is your hypothetical Massive ship bound by the laws of thermodynamics? Real-world machines generate waste heat from every energy-using component, and that heat needs to be transferred to the environment somehow to keep the machine at working temperature. In a vacuum, the only ways to do this are by passive radiation or venting consumable coolant overboard. If you are using passive radiation to keep cool, your ability to eliminate heat will scale with the square of linear size, while the amount of heat you need to get rid of scales with the cube of linear size (assuming homogeneous construction and design, anyway, which is a gross oversimplification.) Therefore, unless you're assuming some kind of thermodynamics-violating cooling method, it will become harder and harder to radiate waste heat the larger a ship becomes.

We can already see this at work with real-world spacecraft. Apollo and Soyuz are small enough to get by with radiators embedded in the outer skin of the craft. The Space Shuttle lines the inside of the cargo bay doors with radiators, and needs to keep them open all the time in orbit. (It also can keep cool by vapor sublimation, but their on-board water supplies are limited). The Space Station needs huge fold-out radiator panels to keep cool. The larger your ship becomes, the more surface area you're going to have to devote to cooling radiators. A sphere is actually the worst possible case from a cooling point of view - minimum radiative surface area per volume.

Of course if you're assuming some kind of laws of thermodynamics-violating cooling technology, or fairly large and frequently recharged tanks of expendable coolant, you can ignore this restriction.

[Simon_Jester]

In terms of moving it I would say some sort of elongated sphere, with the profile of an oval. That way, it is strongest in the direction of primary thrust, and the curved shape should give it enough sheer strength to stand turning. That is, if you want it to be maneuverable and fast.

The word you're looking for is "ellipsoid."

I actually always did enjoy the Executor's proportions...

A sphere works well enough, but it's going to require a LOT of material to build because of its great volume, as does a cube. A more or less flat plane like the Executor, on the other hand, means you can create 4 or 5 ships with the same amount of material that you could use for a sphere of the same width/diameter.

And you also have to consider the function of the ship as well. Does it require a lot of interior space, does it need optimal weapons distribution, will it need thick reactor shielding, etc, etc... A sphere works well for some purposes but for others some shapes might work better.

Yes. Spheres have a minimum surface area per unit volume, which is good if you don't have lots of features you need to mount on the surface and (obviously) bad if you do have lots of stuff to mount on the surface.

Another problem with a sphere is that there is no way to give any weapon an arc of fire of more than about half the sky. Either your main battery is fixed-mount and you turn the sphere to bring it to bear (Death Star), or you mount redundant weapon batteries all over the sphere. With, say, a box-shaped hull, you have a bit more flexibility in terms of how you lay out your weapons, and thus how you define your 'alpha arc,' the region you can fire the greatest possible volume of weapons into.

Also, a sphere has high target profile in all directions: you will be relatively easy to hit from all directions as a result, unless you are very agile. For this reason too, box-shaped or cylindrical hulls are also helpful with spinal armament, in my opinion. They're less bulky than a sphere capable of accomodating a weapon of the same size; this makes it easier for them to sidestep enemy fire. Since you're always trying to fight enemies directly 'ahead' of your main armament, you want to optimize your defense against attacks from that direction, and the most optimal defense possible is not to be hit at all.

So it's worth thinking about those concerns: mass per unit thrust, target profile, armament layout... all those things play a large role in deciding how you want to design your ships. Spheres are great if you expect to be surrounded and don't care about trying to evade enemy fire, but not so great if you're concentrating your armament on fixed-axis weapons and would prefer to evade than to tank the hits.

[Sea Skimmer]

The best shape would be a battle between optimal shapes for structural strength, and optimal shapes for low cost of manufacturing the thing. The requirements for structure strength in turn depend among other things on engine placement and expected maneuverability.

A sphere seems bad in just about every way. It would be expensive to build, it has to be almost equally strong all over, and it needs highly distributed engine thrust or else extremely strength. Something more rectangular like Executor would be easier to make for certain, and probably stronger too because all the mass is stacked ahead of the engines. Acceleration in a straight line would primarily produce a compressive load; and steel is strong as hell in compression. A sphere will have far more shearing and tensile pulls on it. However given a sufficiently massive ship, then compressive limits would be exceeded and the only choice would be to distribute engines more widely; then a sphere isn’t so bad. However a disk with or without some braces might make a lot more sense in turn.

So the answer really is going to lie in just what the hell you want to build in the first place. Form follows function. I don’t think you can build a 100km starship that can move at any significant acceleration out of any real material, so specifying it has a single dimension isn’t that helpful. If we had a mission, desired performance, engine types (do they need 'reactors' or something nearby or just a big cable for electrical power?) if everything needs to be heavily armored or not, and other information then it could be worked out.

[Chaotic Neutral]

Speaking of shapes, how would this include armor? Flat and round are the worst for weapon penetration, no?

[sirocco]

I once tried to tackle the same problem with some kind of 4km wide generational ship. Everything looked sweet until I looked at the actual structural issues (where to put the engine to have maximal thrust for minimal deformation) and thermal issues (where can I still put the radiators).

After modifiying the design 3 times I just gave up =D

http://www.deviantart.com/download/1709 ... y_9nin.jpg

[Purple]

Flat armor is not necessarily worse at all. It depends on the type of load you expect it to face and the material the armor is made from. For example modern tanks use flat sides since the ceramics used in the armor crack when hit at a sloped angle.

It also depends extremely on what level of hardens your setting has. If you are somewhere at Star Trek levels the design you will come up with will be extremely different than what you would do in a truly hard near future setting.

[Simon_Jester]

It also depends on the size of the weapons. If people are slinging around relativistic impactors with nuke-equivalent energy yields, material properties really don't matter very much. What matters is density, and possibly the way different materials interact with different forms of radiation. Structural strength of the armor isn't a big factor, except insofar as you don't want shock waves from the impact ripping the hull frames apart at points far from the impact.

[Crossroads Inc.]

Another problem with a sphere is that there is no way to give any weapon an arc of fire of more than about half the sky. Either your main battery is fixed-mount and you turn the sphere to bring it to bear (Death Star), or you mount redundant weapon batteries all over the sphere. With, say, a box-shaped hull, you have a bit more flexibility in terms of how you lay out your weapons, and thus how you define your 'alpha arc,' the region you can fire the greatest possible volume of weapons into.

Also, a sphere has high target profile in all directions: you will be relatively easy to hit from all directions as a result, unless you are very agile. For this reason too, box-shaped or cylindrical hulls are also helpful with spinal armament, in my opinion. They're less bulky than a sphere capable of accomodating a weapon of the same size; this makes it easier for them to sidestep enemy fire. Since you're always trying to fight enemies directly 'ahead' of your main armament, you want to optimize your defense against attacks from that direction, and the most optimal defense possible is not to be hit at all.

So it's worth thinking about those concerns: mass per unit thrust, target profile, armament layout... all those things play a large role in deciding how you want to design your ships. Spheres are great if you expect to be surrounded and don't care about trying to evade enemy fire, but not so great if you're concentrating your armament on fixed-axis weapons and would prefer to evade than to tank the hits.

A sphere seems bad in just about every way. It would be expensive to build, it has to be almost equally strong all over, and it needs highly distributed engine thrust or else extremely strength. Something more rectangular like Executor would be easier to make for certain, and probably stronger too because all the mass is stacked ahead of the engines. Acceleration in a straight line would primarily produce a compressive load; and steel is strong as hell in compression. A sphere will have far more shearing and tensile pulls on it. However given a sufficiently massive ship, then compressive limits would be exceeded and the only choice would be to distribute engines more widely; then a sphere isn’t so bad. However a disk with or without some braces might make a lot more sense in turn.

So the answer really is going to lie in just what the hell you want to build in the first place. Form follows function. I don’t think you can build a 100km starship that can move at any significant acceleration out of any real material, so specifying it has a single dimension isn’t that helpful. If we had a mission, desired performance, engine types (do they need 'reactors' or something nearby or just a big cable for electrical power?) if everything needs to be heavily armored or not, and other information then it could be worked out.

Well defiantly gives me a lot to think about. I think to begin with, many leap to the sphere because we are so familiar with the DeathStar, one of the few really "BIG" spaceships most everyone knows from SciFi, well that and the lesser know Berzerker which also where sphere like. However the main point form what I see so far is that a Sphere takes a GREAT deal of resources and is rather unwieldy to move around, hence of course my initial thoughts in the OP.

Sea Skimmer has the best point about "form follows function" So the basic 'function of what I had in mind, well the short version.
Basically a high end galaxy spanning Civ (about StarWars tech level) find that the supermassive Blackhole in the center of its galaxy is about to off kilter and flood huge portions of the Galaxy with immense radiation, effectively sterilizing the most populated parts of the Galaxy. Some of the most powerful groups of the Civ deiced to leave the galaxy all together and build "Arc-Ships" Self sustaining mobile fortress command and colony ships. The ships would contain small cities inside for the population, so there would be Immense large open space with an artificial sky. At the same time they are built to be formidable, the Galaxy is going into the carper as everyone freaks out, so military groups are starting to try and take over and such.

After reading some of the comments I am starting to think of a more oval / cone shape to the design. something that would make a simple, engines in back, weapons in front set up more logical. in terms of Armor.. well when you get to the sizes we are talking about, you could have individual, immensely dense plates that could be fitted in any number of shapes. Even rounded would not be hard because at the scale, all those curves could be broken up over innumerable dense plates. Sense it would be around StarWars tech, you would look at the calcs of firepower from what we have in terms of what the ship could expect to be up against.

Also:

Is your hypothetical Massive ship bound by the laws of thermodynamics? Real-world machines generate waste heat from every energy-using component, and that heat needs to be transferred to the environment somehow to keep the machine at working temperature. In a vacuum, the only ways to do this are by passive radiation or venting consumable coolant overboard. If you are using passive radiation to keep cool, your ability to eliminate heat will scale with the square of linear size, while the amount of heat you need to get rid of scales with the cube of linear size (assuming homogeneous construction and design, anyway, which is a gross oversimplification.) Therefore, unless you're assuming some kind of thermodynamics-violating cooling method, it will become harder and harder to radiate waste heat the larger a ship becomes.

I would LIKE to keep things as grounded in reality as much as possible, the ship would generate a Metric Crapton of heat from its engines and Reactors so it would have to be venting just as much. One imagines there are ways of dealing with, not to go back to a Sphere but the DS obviously was able to handle such a thing so I am sure someone has considered what it would entail.

[Simon_Jester]

The death star was entirely handwaved, as far as the tech went. No real consideration of heat problems, for instance.

Basically, if you have a space drive that amounts to teleportation (relatively low energy costs, highly versatile, no need for extensive STL combat maneuvers), you can afford to build giant spheres. Spheres do have virtues, like sheer defensive depth. But if you need engines that work in some roughly Newtonian way, exerting a significant force on the ship, then you want something a bit more linear.

Though there are other interesting possibilities, like a giant flying pie-pan, a disk wider than it is thick. That's one way to circumvent practical limits on how big you can make the ship: effectively build an enormous number of smaller ships that are loosely connected side-by-side, in a modular design. It won't be very maneuverable, but you should be able to make it big.

[Imperial528]

Given what you've said, Crossroads, I should think that a long, thin cylinder would be the best option. Given the size, a very low RPM would be sufficient to generate 1g, and if you're using rotation, then you don't need energy and heat costs going into silly a-grav devices. Additionally, a cylinder offers a small target profile, especially at a distance since anyone trying to attack it would find themselves aiming at a line unless they got in close. The shape also allows rather straightforward engine design. If the plan is to leave this galaxy, one could expect that the path is going to be more or less a straight line, so what you could do is have rotating modules around a strong core which is attached to the non-rotating engine and thruster modules that move the ship.
Which brings us to armament and defenses. For armor, the best idea I can think of at the moment is to have a second cylinder made up of the individual plates mounted to a frame. One could also decide to mount the weapons on this second cylinder, which essentially gives you a three layer ship: "Core"; power, fuel, and engine modules. "Filling"; living spaces, food production, etc. And "Shell"; defensive and offensive capabilities.
Which leaves the issue of heat. Out of combat, the entire armor surface, if designed correctly, would be a perfect radiator for the inner sections, since it is essentially a giant hunk of metal. Which brings us to heat radiation during combat, which would still work to use the armor as a radiator, but it would also likely compromise the armor against most weapons. Really, having a disposable coolant for combat heat management would be best.

[Sea Skimmer]

Speaking of shapes, how would this include armor? Flat and round are the worst for weapon penetration, no?

Rounding off armor used to matter with shells because it could make them skip off. With modern HEAT fuses and long rod sabots it’s unlikely anything would make the round deflect except an extremely shallow impact angle (in which case it would skip off a flat plate too) so its no longer a very useful advantage. Modern armor is all about putting as much thickness and density of material in front of the projectile as possible, often by exploiting material that deforms under impact. Any kind of realistic space warship armor for a heavy warship intended for direct combat is going to need to be thick as hell (not necessarily all that dense) and include numerous layers and void spaces.

A major factor in armor choice will be the armor mass fraction. Depending on how much sci tech is involved a warship may not be able to afford dedicated armor material. It may be that all armor must also serve as structure, which would seriously constrain material and design choices. In just about any case I would expect fuel to be used as armor. Ships would also be heavily compartmented and further subdivided by armor, because you can’t sink so this is only highly logical and you’ll need lots of heavy bulkheads for strength anyway. Redundant local power and life support gear would further support that, as the men may have to wait months or years for rescue after surviving heavy damage.

A ship fueled by ‘fast fission’ or similar nonsensical combustion of millions of uranium fuel rods would be an awesome example of fuel-armor. You could have them all stacked up around vital spaces and magazines and constantly have officers nervous about keeping fuel levels high so fractional C throwing darts can’t explode the torpedoes.

[Purple]

Could the same not be achieved much more cheaply by simply applying some ludicrously small rotation to the ship? If it has any sort of maneuvering capabilities this should be easy and it only needs a bit of trust for the inertia to do your job for you.

And in case of war ships this might also help you bring all your weapons to bear on an enemy over time allowing you to make up for any damages to those on one side. There is no need to use broad sides in space.

[Simon_Jester]

I don't like this solution.

It's mechanically complex, requiring multiple layers of rotation bearings for the armor panels and a drive train to keep them spinning. Depending on how much of the ship's mass is spinning in this way, the torque can be an issue if anything breaks, and the armor's ability to protect against kinetic impactors is severely compromised.

And at ranges short enough that the enemy really can focus a laser on a spot small enough that this is useful, for periods long enough that this system is useful, it is very much viable to lob guided missiles (or, hell, glorified cannonballs) at you and rely on brute force to smash through all those spinning plates.

Sounds cunning, but it's got too many moving parts, and too much optimization against a single threat type, to be a good passive defensive scheme.

[Purple]

That and I imagine the joy of anything breaking and the armor spinning out of control on its own momentum ripping the ship apart in the process.

[Imperial528]

This is just speculation, but perhaps a combination of reactive/reflective armor would be best? If the compound that makes up the reactive armor has a high enough concentration that the surface layer of each brick of reactive armor can reliably refract a laser of the same energy as the kinetic projectile it is designed to repel, then you have a pretty good armor, especially if it is made in layers, so that the same spot can be hit multiple times. It's probably also wise that it be mounted on a layer of good old dense armor plate that is coated in a reflective substance, so that sustained fire won't be as effective on it. The bonus is that the entire thing is almost completely solid-state once deployed, especially if the reactive armor is triggered by being hit at a certain speed or size of object rather than through the use of sensors.

[Purple]

This is just speculation, but perhaps a combination of reactive/reflective armor would be best?

Reactive armor as in active reactive (ERA/NERA) or as in armor that enters into a chemical reaction. Because the term Reactive Armor is usually used to describe ERA plates.

I mean, if you want anti laser ERA the simplest thing would be to have some way of projecting a cloud of particles into the beam to disperse it.

[Simon_Jester]

You don't want ERA against lasers, or I wouldn't think you would. Ideally, you want something that will vaporize into a fogbank, which temporarily disperses the beam and limits its effect. Or something that's extremely difficult to burn off and rotating (spinning the ship helps; firing maneuvering thrusters randomly can help more in my opinion).

"Armor" that explodes into the path of an oncoming projectile is a specialized counter to a specialized type of threads. I'm really not sure it would translate well into space combat at all, though there are people I respect who believe it would.

This is just speculation, but perhaps a combination of reactive/reflective armor would be best? If the compound that makes up the reactive armor has a high enough concentration that the surface layer of each brick of reactive armor can reliably refract a laser of the same energy as the kinetic projectile it is designed to repel, then you have a pretty good armor, especially if it is made in layers, so that the same spot can be hit multiple times. It's probably also wise that it be mounted on a layer of good old dense armor plate that is coated in a reflective substance, so that sustained fire won't be as effective on it. The bonus is that the entire thing is almost completely solid-state once deployed, especially if the reactive armor is triggered by being hit at a certain speed or size of object rather than through the use of sensors.

Well, optimum armor design is sure to be some kind of sandwich of layered passive defenses. The exact composition is hard to say: would reactive armor be all that helpful against hypervelocity impactors that crater rather than penetrate the armor? What does it mean to make "reactive armor" that "can reliably refract a laser of the same energy as the kinetic projectile it is designed to repel?"

This is a complicated subject. The dynamics of high-speed impacts on armor plate are already a very complex, very technical subject. The variety and nature of threats faced by armor on a hypothetical spacegoing warship would make the issue even more technical.

[Imperial528]

@Purple: I meant ERA, yes, but the ERA part for projectiles, with the surface plate being reflective, unless you could create a reliable hybrid ERA that works against KEW and DEW.

@Simon_Jester: I mean that each brick of ERA has a coating that would reflect/refract/otherwise neutral a laser pulse hitting it that contains an equal amount of energy as a kinetic projectile that a single brick of ERA would effectively protect against.
Although if we're talking high-speed as in hyper-velocity, then I'd just go with thick layers of, well, anything that's dense and cheaply produced in large quantities to be effective.

[Spectre_nz]

Mostly already covered, but the size of your void spaces becomes increasingly important as the velocity of the kinetic impactors you expect to face goes up. Empty fuel tanks and seldom used crew-compartments also function well as void spaces, if you're prepared for a little damage control.

As far as resisting laser weapons goes, this is my pet solution and may be total bollocks if I haven't thought about it hard enough, but I'd pair a 'field' of plasma around the ship with an outer layer of plastic impregnated with sand (actually, tungsten carbide grit) as an ablative appliqué for the whipple shield armour.
Laser bloom is something of a problem in an atmosphere, so why not give a ship its own small atmosphere of plasma. Then your opponent wastes laser energy heating your plasma ball and not your ship.
Then under that, plastic and grit. Plastic vaporizes ejecting vapour and carbide grit out into the path of the beam. Carbide has a high heat of fusion and further diffuses the laser, just like suspended dust in the atmosphere does.

As I said, my pet solution, for a hard-ish sci-fi setting. Effectiveness depends on how much plasma you can tolerate holding around your hull vs how high energy the lasers you're facing are, and if you can stand you ships ending up looking like fluorescent lights.

Edit: Or, you can just handwave starwars shields and be doen with it.

[jollyreaper]

I don't think there is any universal truth here. It all depends on the tech of the setting and personal preference.

I find that rationalizing the hypothetical tech can yield interesting designs. Form follows function and fictional tech looks better when people give it some thought.

I'm still very partial to the design of the mothership from homeworld. That was one classy ship. Also a fan of the guild ships from the dune miniseries.

[Purple]

I completely agree. The original mothership from HW1 was just epic.

This said, if laser weapons are used by both sides would it not be simple to store old used up coolant and just flush it into the general direction of an enemy laser making a smoke screen. That should cause quite a lot of bloom at a fraction of the cost of creating plasma shields.

[Crossroads Inc.]

Mang didi anyone read my last post? I said this was a StarWars tech Civ, you have that to work with