Ship Design Philosophy

Discuss the Traveller RPG and its many settings
Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Tue Oct 22, 2013 9:30 pm

The Jump drive doesn't care what's within it's sphere, just the mass. There are two precedents it's possible, grappled craft and drop tanks. Welding is quite possible, and would follow a modular concept.

The tricky part is the wiring, and if you kept fuel in the secondary hulls. For ease of control, the primary hull could hold the bridge, the engines and the fuel.

I'm surprised no one else didn't come up with a similar scheme. You could set up a short haul passenger/courier company, which we could call RyanSpace.

RyanSpace leases/buys new hundred ton hulls. Because the order size would be large, further discounts are involved. The company either skims gas giants itself or obtains long term fuel contracts at favourable prices.

The drives would be standard Bs, spare parts available at most starports, and so easy to maintain that a monkey with wrench could do it.

A single pilot cross trained as an engineer could handle the freight runs. A designated flight engineer and a medic would be required for passenger runs.

You configure Jump 2 express runs with a single secondary hull. The normal configuration would be three secondary hulls on Jump 1 routes.

RyanSpace would prefer it's passengers all choose Economy class, 189 low passage seating in one hull. They'll reintroduce no frills Business Class, forty passengers per secondary hull with two stewards.

Freight would be carried in the standard hundred ton container.

At the end of the lease or manufacturer's warranty, the hulls are replaced, since it's cheaper to get new ones (due to safety and maintenance concerns) than refurbish old ones.
dragoner
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Re: Ship Design Philosophy

Postby dragoner » Tue Oct 22, 2013 9:59 pm

The process of attaching the hulls together would probably equal the cost of the bigger hull. BUT, it is still an interesting dispersed structure design. :)
Yatima
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Re: Ship Design Philosophy

Postby Yatima » Wed Oct 23, 2013 10:35 am

The process of attaching the hulls together would probably equal the cost of the bigger hull.
The rules are broken in this respect, I would argue.

When you choose a distributed hull configuration in step 1 of the design process you are essentially saying that the ship you are making is a collection of parts bolted together and not a single monolithic enclosing shape with bits contained inside. This saves you 10% on the hull cost, which is too little, I think.

Now, High Guard (p. 41) states that up to 75% of a ship can be modular (excluding bridge & drives) but this increases the cost of the hull by that percentage – so up to 175%.

This makes no sense to me and is overpriced. I think the author had a monolithic hull with clever modular internal add-ons in mind when creating this rule. What if I want to build a long structural truss with drives and power plant at one end and a bridge and crew quarters at the other (picture the Discovery from 2001. I want the truss to support my adding on cargo modules, extra living space, spin habitats and a series of drop fuel tanks attached to the truss. This enables me to reconfigure the spacecraft from one mission to the next. Does this hull cost 175% of the price, or 90% as a distributed hull?

GURPS Traveller starships handles this more sensibly IMHO:
A dispersed hull is a structure with a minimum of open frame armor, to which components are attached. The hull itself cannot be sealed or pressurized; instead, separate sub-hulls are constructed and attached to the frame to provide pressurized environments.
You make the frame which is 20% of the usual cost of hull with the selected armor value, and design and attach the sub hulls as individually designed components. This is much more flexible, and realistic and enables you to design ships that do not share the underlying assumption that a spacecraft is a sealed tub, and the design process involves stuffing that tub with sub-systems.

GURPS sub-hulls cost nothing extra - but they are not removable. To make them removable (modular), you add a modular socket, which allows you to add a removable component of a given volume. The sub-hull module would cost a mere 20% extra (which I presume models grapple points, airlocks, power and data links etc. and is fair enough).

J

PS: This sort of system is a much better one for modelling ships from 2300AD or Orbital as well as OTU ships from less advanced worlds.
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dragoner
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Re: Ship Design Philosophy

Postby dragoner » Wed Oct 23, 2013 2:14 pm

Yatima wrote: The rules are broken in this respect, I would argue.
I wouldn't say they are broken, just a different set of assumptions. Such as with the Discovery, iirc, it was built that way to keep the propulsion unit away from the hab module. From an engineering standpoint, the dispersed structure ships are not that great as they would naturally tear apart under the stress of acceleration with trav m-drives. In those GURPS descriptions, the term hull is used incorrectly and open framed armor ... what? The Mongoose rules are ok, they work within whatever standard there is of trav starship rules.
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Re: Ship Design Philosophy

Postby Yatima » Wed Oct 23, 2013 2:50 pm

dragoner wrote: I wouldn't say they are broken, just a different set of assumptions.
True, Dragoner, not broken in the sense of mechanically inconsistent. More specifically, I would say they are:

1. Simplified to the point of making it difficult to represent many reasonable designs one could conceive of that should be possible to build.
2. Based on assumptions that make the costs proposed higher when you'd expect something to be cheaper, because it's simpler or uses less materials.

Of course, YMMV.

As to toleration of high accelerations, this is another matter the rules represent simply using hull and structure points, which is fine. But there isn't any good reason a distributed hull cannot be rated for higher G operations as well as a enclosed (or Standard) hull. The rules just abstract these considerations away, making them a matter for deck plan design and visualisation.



J
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dragoner
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Re: Ship Design Philosophy

Postby dragoner » Wed Oct 23, 2013 3:15 pm

Yatima wrote:
dragoner wrote: I wouldn't say they are broken, just a different set of assumptions.
True, Dragoner, not broken in the sense of mechanically inconsistent. More specifically, I would say they are:

1. Simplified to the point of making it difficult to represent many reasonable designs one could conceive of that should be possible to build.
2. Based on assumptions that make the costs proposed higher when you'd expect something to be cheaper, because it's simpler or uses less materials.

Of course, YMMV.

As to toleration of high accelerations, this is another matter the rules represent simply using hull and structure points, which is fine. But there isn't any good reason a distributed hull cannot be rated for higher G operations as well as a enclosed (or Standard) hull. The rules just abstract these considerations away, making them a matter for deck plan design and visualisation.



J
Points one and two somewhat contradict each other, but imo, I don't want more complex starships, that happened with MegaTraveller and I hated them, plus it merely showcased how little of practical engineering they understood. With anything aerospace, generally materials are the cheapest portion, the labor of building and designing are going to be the biggest costs. As per a dispersed structure versus a regular hull and G forces, per real world physics, the tighter the structure, the more resistant it is to the G forces; if then a dispersed structure was made to be able to handle it, it would be about of the same cost as a unified structure - my original point.
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Re: Ship Design Philosophy

Postby Yatima » Wed Oct 23, 2013 4:16 pm

dragoner wrote: Points one and two somewhat contradict each other, but imo, I don't want more complex starships, that happened with MegaTraveller and I hated them, plus it merely showcased how little of practical engineering they understood. With anything aerospace, generally materials are the cheapest portion, the labor of building and designing are going to be the biggest costs.
As I said YMMV. I don't want more complexity for it's own sake, just a system that allows me to express ideas without running into the boundaries of the possible too easily. A little more flexibility would be welcome.
dragoner wrote: As per a dispersed structure versus a regular hull and G forces, per real world physics, the tighter the structure, the more resistant it is to the G forces; if then a dispersed structure was made to be able to handle it, it would be about of the same cost as a unified structure - my original point.
Your first point is undeniably correct, your second may or may not be true, but without a specific structure to discuss we'd only be handwaving and generalising in a way that proves nothing much. You may find this article interesting if you hadn't seen it before:

Ship Structure and Hull Size Limitations, by Christopher Thrash

This analyses the structural properties of traveller hulls under acceleration using guidelines from the currently accepted text book on space craft design, SMAD III. It's a fascinating read.

J
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dragoner
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Re: Ship Design Philosophy

Postby dragoner » Wed Oct 23, 2013 4:34 pm

Interesting article, but he only uses a monocoque-columnar structure, which would preclude a dispersed structure; the difference would be very big in replacing skin tension stress with the structural stress points of strut connections. The inertial momentum the various smaller masses would be borne by the strut connections, both in the design of the body of the struts and how they attach through.
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Re: Ship Design Philosophy

Postby Condottiere » Wed Oct 23, 2013 7:56 pm

There are two aspects to consider - 2 MCr covers a standard hull; a pure freight container should be cheaper, theoretically.

The secondary hulls could conform to the primary hull.
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Re: Ship Design Philosophy

Postby Yatima » Wed Oct 23, 2013 9:24 pm

dragoner wrote:Interesting article, but he only uses a monocoque-columnar structure, which would preclude a dispersed structure; the difference would be very big in replacing skin tension stress with the structural stress points of strut connections. The inertial momentum the various smaller masses would be borne by the strut connections, both in the design of the body of the struts and how they attach through.
Yes, and by putting the drives at the back of the 'tower' that design needs more structural strength to withstand being pushed along. One design that's really interesting is the ship in Avatar, which puts the drives at the front and pulls the rest of the ship instead, thereby saving on mass because the tower does not need to be as strong. Nice piece of work, all the same.

J
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dragoner
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Re: Ship Design Philosophy

Postby dragoner » Wed Oct 23, 2013 10:59 pm

Yatima wrote:
Yes, and by putting the drives at the back of the 'tower' that design needs more structural strength to withstand being pushed along. One design that's really interesting is the ship in Avatar, which puts the drives at the front and pulls the rest of the ship instead, thereby saving on mass because the tower does not need to be as strong. Nice piece of work, all the same.

J

Yes, it is interesting; and I want to say is that I do NOT want to dissuade anyone from doing dispersed structure designs. No. 1&2 design elements should be fun and creativity.
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Re: Ship Design Philosophy

Postby locarno24 » Thu Oct 24, 2013 7:46 am

F33D wrote:Actually, the rules don't allow for welding together a bunch of different complete hulls to make a ship. No matter what the config is. See hull prices.
They do and they don't. If you really want a multi-component ship (as opposed to 'distributed' being nothing more than a hull type code), then build your hull sections and fit them together with docking clamps from High Guard.

I've done that on occasion to allow for 'sub ship' elements - for example, the limit of one spinal mount per ship (regardless of the percentage of the ship it occupies) means that a clamped on 'heavy gun mount' might be sensible for a super-heavy capital ship.
Understand that I'm not advocating violence.
I'm just saying that it's highly effective and I strongly recommend using it.
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Re: Ship Design Philosophy

Postby Condottiere » Thu Oct 24, 2013 10:07 am

There's an old cartoon movie, a rip off from Star Wars, which impressed by the fact that the ship engines were placed on rotatable pylons that changed direction to allow thrust to be applied as a break or when landing.
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Re: Ship Design Philosophy

Postby SSWarlock » Thu Oct 24, 2013 11:40 am

Condottiere wrote:There's an old cartoon movie, a rip off from Star Wars, which impressed by the fact that the ship engines were placed on rotatable pylons that changed direction to allow thrust to be applied as a break or when landing.
And don't forget the "Serenity" from the Firefly TV series and movie.
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Condottiere
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Re: Ship Design Philosophy

Postby Condottiere » Sat Oct 26, 2013 8:37 am

Firefly is supposedly iconic, yet I really only remember the character archetypes. And Christina Hendricks. And Morena Baccarin.

Are the Solomani still committed to their doctrine of commercial raiding, and is there a current order of battle? With reaction drives and the need to secure and transport sources of fuel, this doesn't really seem a very viable strategy to base the majority of the fleet on for an extended war.
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Re: Ship Design Philosophy

Postby coldwar » Sat Oct 26, 2013 7:54 pm

I've done that on occasion to allow for 'sub ship' elements - for example, the limit of one spinal mount per ship (regardless of the percentage of the ship it occupies) means that a clamped on 'heavy gun mount' might be sensible for a super-heavy capital ship.
Thats given me a couple ideas for my Universe.
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Re: Ship Design Philosophy

Postby Condottiere » Sat Oct 26, 2013 10:03 pm

I had them on grappled battleriders equipped with batteries, using the battleship as command and fast getaway.
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Re: Ship Design Philosophy

Postby Condottiere » Mon Oct 28, 2013 11:02 am

Fighter design is an interesting dilemma. Light fighters tend to serve as trainers, counter-insurgency, close air support, tactical reconnaissance, patrol, second line interceptors.

Classic ones go as small as six tons. Current theory goes that a netcentric swarm could probably overwhelm a less flexible opponent. Frankly, I doubt that's really a viable strategy against an aware opponent, besides the fact that you're spending an awful amount training the pilot in both time and operating costs, though that's a current perspective, and doesn't include the potential effectiveness of future simulation ground facilities/programmes, skill software implant transfers, and mass production, the economies of scale and millions of eager volunteers.

Constraints for light fighters would be pilot and fuel endurance, and while I believe most pilots would regulate cockpit gravity to make sitting for hours in the acceleration couch a pleasant experience, you probably want to reel them in after eight hours on station. There are no freshers onboard, and diapers only last so long. Stillsuits might be an option. Mongoose should do Dune.

So you build around the 1.5 ton acceleration couch, a cheap Model One computer, an sG power plant for a beam laser at 3 tons (an sA power plant at 1.2 tons if not), and a ton of fire control. Plus basic civilian electronics at a ton.

So how much does a fixed mount weigh? You need enough space in a turret for an operator and three weapons, so that should work out to be around one hundred to two hundred kilos. A missile should weigh around eighty kilos.

Two interesting questions are, how long do you expect the battle to last, and how long do you expect the pilot to be able to carry out his mission. This reflects on the maximum ammunition he needs to have, and the optimum amount he should take with him. This determines if an energy weapon or a missile rack is a better fit. The difference would be three kilos minus one point two, which gives us one point eight tons, or twenty one missiles, not counting the one in the chamber. It should be noted, that I would find it a little strange if anyone authorized nuclear missiles to be issued to light fighters.

So, let's incorporate a half a ton magazine, which gets us to 4.2 tons, an sB reaction drive, which leaves, enough for three hundred kilogrammes of fuel, for two hours of serious partying, at around 8Gs.

So that would be a five ton ultralight space fighter. Though my maths is probably off.

Speaking of maths; the hull probably costs 750'000, streamlining 75'000, stealthing 500'000, reflecing 500'000, self sealing 50'000, maybe 850'000 for the mounted missile rack, 130'000 for the bridge, 4'000'000 for the drives. 6'855'000, not counting missiles, anti-personnel weapon or production discounts.
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Re: Ship Design Philosophy

Postby Condottiere » Tue Oct 29, 2013 6:16 pm

I appear to have been remiss.

TL 9 missiles are either 60% smaller, or can have three upgrades. Radiation shielding comes at 1'250'000, heat shields at 500'000.

An interesting option is to turn it into a drone with more austere features.


The civilian version could substitute a Grav drive model sA at 3.2 tons with standard electronics, with 1.8 fuel/cargo, or upto three passengers at 4Gs. A lite skiff sounds an appropriate description. Or a space-taxi. Aerofins at 250 kilos at 500'000.
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Re: Ship Design Philosophy

Postby Condottiere » Thu Oct 31, 2013 6:14 am

Speaking of Grav drives, they seem to be the game's equivalent to diesels, since they require no extra fuel besides that of the power plant. The CEO of RyanSpace will have all reaction drives replaced by smallcraft Grav drives in order to cut down on fuel usage, besides the fact that a constant acceleration will move the spacecraft to and from the jump points to the terminals much faster, speeding up the turnaround rate.

For capitol ships and heavy fighters, I'd use them for cruise, and reaction drives as afterburners.


I notice that smallcraft individual torpedo tubes don't need fire control, meaning that a TL 12 torpedo weight 1.5 tons could conceivably be loaded on a five ton torpedo bomber, though the picture you get is closer to this:

Image

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