Newtonian Aurora

[bean]

On ship structure and acceleration:

Given that we have a rough measure of how resistant TN materials are, would it be possible to enforce a ship size restriction based on weight and acceleration?

Since the acceleration of the ship comes from the engines, the front bits will press onto the back bits and there is a "limit" to how big you can build a ship before the walls crumple under the ever-so-huge nuclear torch drives. 

Might be in the hundred thousand tons or so but I have qualms about imagining what goes on in a twenty million ton orbital habitat that's under tow by a fleet of tugs.  1G on that?  Your structure might just break if your materials aren't good enough. 


EDIT:
basically, I'm suggesting a safe acceleration limit based on (weight of ship / armor tech level), capped to 3x racial gravity tolerances.
And yes, this means that an unladen freighter will have a higher acceleration limit than a fully laden one, which is only expected. 

Exceeding the limits might cause equipment to "age" far faster than usual, based again on percentage exceeding the limit.  Exceeding racial gravity tolerances might cause crew death. 

EDIT EDIT:
Might balance gravity in an interesting way too. 

Higher G races make better crews but have less qualifying planets.  Low G races can't accelerate as fast but can colonize many moons. 

I like the suggestion that certain types of things have limits on acceleration.  I would add a "space station" switch.  You can make the vessel cheaper, but max accel, even under tow, is only about .1G.  It's not a big issue for ships unless you get unreasonably large.  And by that I mean into the hundreds of thousands if not millions of tons, particularly with TN materials.
The racial acceleration thing is already included.

[Steve Walmsley (OP)]

On ship structure and acceleration:

Given that we have a rough measure of how resistant TN materials are, would it be possible to enforce a ship size restriction based on weight and acceleration?

Since the acceleration of the ship comes from the engines, the front bits will press onto the back bits and there is a "limit" to how big you can build a ship before the walls crumple under the ever-so-huge nuclear torch drives.  

Might be in the hundred thousand tons or so but I have qualms about imagining what goes on in a twenty million ton orbital habitat that's under tow by a fleet of tugs.  1G on that?  Your structure might just break if your materials aren't good enough.  


EDIT:
basically, I'm suggesting a safe acceleration limit based on (weight of ship / armor tech level), capped to 3x racial gravity tolerances.
And yes, this means that an unladen freighter will have a higher acceleration limit than a fully laden one, which is only expected.  

Exceeding the limits might cause equipment to "age" far faster than usual, based again on percentage exceeding the limit.  Exceeding racial gravity tolerances might cause crew death.  

EDIT EDIT:
Might balance gravity in an interesting way too.  

Higher G races make better crews but have less qualifying planets.  Low G races can't accelerate as fast but can colonize many moons.  

Really good point about racial gravity tolerances. I will definitely add something along those lines at some point. Maybe some type of crew grade penalty at lower levels and chance of crew injury/death at higher levels. I will have to introduce some type of penalty for undermanned ships for that reason, plus I will likely be adding radiation effects on crews as well. The radius of damage from nuclear weapons might be far less in space but the radius of radiation effects is actually greater than in atmosphere.

Some form of structural limitation on large ships is also a good idea. I'll give some thought to the mechanics of that.

Steve

[TheDeadlyShoe]

Isn't it going to be antigravity minerals or somesuch? Doesn't seem to square with racial acceleration limits. Unless it's like, you can counter gravity but not manipulate it. 

[Elouda]

Ill bring up a suggestion I made a while back for accelerations;

Up to a certain multiple (say 3x) of maximum gravity tolerance, just suffer penalties (such as crew grade). Beyond this (up to say 5x), disable the ability to actually give orders to ships, beyond perhaps a 'stop accelerating', which will take a while to take effect (like current order changes). Im not sure if weapons should still work at this stage, maybe only totally automated things like PD. Going even further results in the same penalties and crew death.

Live cargoes such as troops and colonists might have their own limits, so while your space crew can handle 4.5g acceleration, the troops might only be able to bear 3g, and the colonists 1.5g, assuming theyre even of the same race.

[Yonder]

Having an acceleration limitation separate from racial tolerances is IMO a good idea. The larger a ship is the less acceleration it should be able to take (assuming it doesn't grow purely in width) for the same reason that a building can only get so tall. Think of the engines as being the base of the building, with the acceleration the strength of the gravity. As the building gets taller for the same amount of gravity more and more force is being placed on it. (Making the building wider, but no taller, brings no change). As a spaceship gets larger it's like making the building larger, the portion of it that corresponds to a wider building doesn't change the force, but the portion that corresponds to the building getting taller requires a stronger building.

This is due to the square-cube law. As the building/spaceship gets larger the force on it diminishes with it's surface area (the square) but increases with the mass (the cube).

The reason that this is necessary from a gameplay standpoint is that it's the only thing that will allow small ships to be faster than large ships. As it is right now (rightfully IMO) the engine techs will be "Thrust per Ton" modified by a thrust modifier and a size modifier. There isn't anything stopping you from designing both your fighter and your battleship engines from being +100% thrust, then putting 20% engine mass on them, and having them each go the same exact speed.

However we don't want an arbitrary size restriction stopping that from happening, we want organic and realistic rules that are the same across the entire spectrum of hull sizes. I can see two ways of doing that, the first similar to what JSeah is talking about.
1a. Maximum acceleration limits for ships based on structural strength and size:
A_max = ArmorStrength / Tonnage^1/3
Where ArmorStrength would be a multiplier assigned to each tech level of armor.

For example:
If your ArmorStrength at your tech level was 200 then you'd have some of the following max Accels:

Tonnage	MaxAccel (m/s2)
250	31.7
1000	20
3000	13.9
15000	8.1

If you research the next level of armor, your ArmorStrength would go up (say to 300) and your max accelerations for ships with the new armor would go up. You could either put on new engines, or more of the old ones.

1b. Another possibility is to modify the above formula by adding in armor thickness to the mix. On one hand this makes a lot of sense, if you are making a stronger ship then the structure can take more wear and tear, on the other hand how exactly could we calculate that? The armor is just along the outside of the ship, so the larger the ship the less the armor can help the internals at the center of the ship. I would have to dig out my Structure textbooks from college to see how that scales, and I don't want to. It's also ignoring the possibility of internal bulkheads, which you would obviously reinforce if you were going for more acceleration resistance than weapon resistance.
Lets try adding in a multiplier based on the Square Root of the armor thickness, and see what that gives us.
A_max = ArmorStrength * ArmorThickness^1/2 / Tonnage^1/3

For example:
If your ArmorStrength at your tech level was 200 then you'd have some of the following max Accels:

Tonnage	Armor Thickness	MaxAccel (m/s2)
250	1	31.75
1000	2	28.28
3000	4	27.73
15000	10	25.64

If we wanted to go this route someone could either try to juryrig up some math to polish it up, or we could decide on the Armor Thickness effect that gives us the feel that we are aiming for. Personally I think that that last  equation makes it too easy to make super fast big ships, but that original one that doesn't take into account armor thickness is probably too penalizing.

2. I mentioned a second way, also based on the square cube law (as I suppose all realistic size mechanics would be). I'm not going to try to develop any equations for them, but the idea would be that the heat developed by an engine scales linearly with it's thrust (aka the tonnage) but the heat can only escape with respect to the surface area (aka a multiple of tonnage^2/3. You could use calculate some sort of maximum thrust ceiling that was more favorable to small engines than big ones. I like the structure-based approach much better for a couple reasons:
1. Steve hasn't modeled thermal effects that much before, so it's an odd mechanical addition to the game.
2. As described you could actually get around the effect with a lot of small engines on your big ship, which wouldn't work IRL because the engines would be bleeding heat into each other, so the ones in the center would overheat, so I guess you'd need to work ship-wide to find the total engine tonnage.

[jseah]

Another thing I realized about doing this:

If we impose limits onto maximum accelerations of equipment, this nicely leads into railgun-assisted launches.  At least, you can tack a number onto it and say "this size railgun can impart total X velocity to launch, capped by max accel and railgun length, or by energy if the railgun is too low powered"

[Elouda]

Not sure if this has been brought up yet, but with regards to railguns and launching things...any chance we might see an EM 'catapult' for launching fighters or gunboats from large carriers?

[bean]

Not sure if this has been brought up yet, but with regards to railguns and launching things...any chance we might see an EM 'catapult' for launching fighters or gunboats from large carriers?

Unlikely for physics reasons.  If we assume the crew can take 10Gs, a catapult will be about 2.5 km long for a 1 km/s delta-V.  I don't think we'll have ships that big.

Yonder:
I'm not so sure that there are such fundamental structural limitations, particularly for warships. 
First off, there are two ways that a ship can suffer structural failure (provided we model it as a column).  The first is buckling, while the second is simple yielding.  The resistance to yielding scales directly with area, or with the square of length scaling, or the 2/3 power of  mass scaling, provided we assume that all vessels are of the same proportions.  Resistance to buckling scales with the fourth power of radius, and with the 4/3 power of mass scaling.
The point is that bigger vessels will have an advantage in resisting buckling, and a disadvantage in resisting yielding.  I'm not sure where the two lines cross, but as I said earlier, I don't see it as being a major problem for reasonably-sized vessels.
On the other hand, if you do use armor as part of the structure (and there's no reason not to) military vessels will most likely be capable of higher accelerations then civilian vessels.  Then again, when said cargo ship is empty, he can pretty much go as fast as he wants.

[jseah]

The point is that bigger vessels will have an advantage in resisting buckling, and a disadvantage in resisting yielding.  I'm not sure where the two lines cross, but as I said earlier, I don't see it as being a major problem for reasonably-sized vessels.

But when this is a missile mounted in a railgun, then the question becomes relevant. 

True, a crew can't take the accel of a railgun launch.  But missiles are unmanned. 
True, a missile is small compared to a ship and TN materials are unobtanium-strength.  But likewise, this is some massive accelerations here. 


I still want that railgun-assisted missile launcher. 
And I don't want to see too many engines on a multi-million ton orbital. 

[bean]

But when this is a missile mounted in a railgun, then the question becomes relevant. 

True, a crew can't take the accel of a railgun launch.  But missiles are unmanned. 
True, a missile is small compared to a ship and TN materials are unobtanium-strength.  But likewise, this is some massive accelerations here. 


I still want that railgun-assisted missile launcher. 
And I don't want to see too many engines on a multi-million ton orbital. 

Are you sure you got the right quote?  I was talking more about ships during the post on structure.
I can see missiles being launched with some velocity.  If the missile can take 100 Gs, the launcher only needs to be 500 meters.  Still too long.  For 1000 Gs, the launcher is 50 meters.  So I would say that it is possible for a few km/s for missiles, but not much more.
And please note that in the absence of artificial gravity, an orbital hab is not a cylinder.  It's a disc.  I would put an accleration limit on certain components, such as orbital habs and cryo spaces.

[Steve Walmsley (OP)]

However we don't want an arbitrary size restriction stopping that from happening, we want organic and realistic rules that are the same across the entire spectrum of hull sizes. I can see two ways of doing that, the first similar to what JSeah is talking about.
1a. Maximum acceleration limits for ships based on structural strength and size:
A_max = ArmorStrength / Tonnage^1/3
Where ArmorStrength would be a multiplier assigned to each tech level of armor.

For example:
If your ArmorStrength at your tech level was 200 then you'd have some of the following max Accels:

Tonnage	MaxAccel (m/s2)
250	31.7
1000	20
3000	13.9
15000	8.1

If you research the next level of armor, your ArmorStrength would go up (say to 300) and your max accelerations for ships with the new armor would go up. You could either put on new engines, or more of the old ones.

I really like the idea in general and the above suggested formula specifically. If we ignore thickness for simplicity but instead use the current armour strength as a measure of 'current materials technology', we can assume that as armour increases in strength, the materials from which the entire structure of the ship is constructed, improve at a similar rate. This idea of using the unspecified material from which the entire structure is constructed avoids the complication of armour thickness as that is just around the exterior of the ship. Armour strengths at each tech level are as follows:

60, 80, 100, 125, 150, 180, 225, 260, 310, 375, 450, 560.

Bearing in mind that engine technology improves as well and that at low tech levels the acceleration rates will be low anyway, the above formula should be fine.

Steve

[bean]

I really like the idea in general and the above suggested formula specifically. If we ignore thickness for simplicity but instead use the current armour strength as a measure of 'current materials technology', we can assume that as armour increases in strength, the materials from which the entire structure of the ship is constructed, improve at a similar rate. This idea of using the unspecified material from which the entire structure is constructed avoids the complication of armour thickness as that is just around the exterior of the ship. Armour strengths at each tech level are as follows:

60, 80, 100, 125, 150, 180, 225, 260, 310, 375, 450, 560.

Bearing in mind that engine technology improves as well and that at low tech levels the acceleration rates will be low anyway, the above formula should be fine.

Steve

I'm going to disagree rather strongly with the specific formula.  I like the one that includes armor thickness better, as it provides a distinct gap between military and civilian vessels, particularly at larger sizes.  For one thing, the armor should be included in the hull structure.  For another, it provides a tradeoff between armor and speed, which turns Jackie Fisher's claim that "Speed is armor" on its head.  I guess my biggest problem is that instead of being a penalty on bigger ships, it's a sharp limit.  If you wish to build something at 60,000 tons (which I have done) it just won't go that fast no matter what.
A couple of other issues.  First, how is the limit measured?  This actually applies to all formulas.  Is it for the full-load mass, the empty mass, or the current mass?  For another, at low tech levels, a civilian ship will have absurdly low accelerations.  A "standard freighter" (the one outlined in the tutorial, or it's equivalent with 5 bays) is limited to around 1.8 m/s2 at the beginning.  That may be normal, or it may be a major headache.  However, the same ship at the end is limited to around 17.3 m/s2, which seems a little high for a civilian ship, but low for a military vessel. 
Just my opinion, but I would include armor thickness as well, which would allow more flexibility for the player in determining the capabilities of his vessel.

[Steve Walmsley (OP)]

I'm going to disagree rather strongly with the specific formula.  I like the one that includes armor thickness better, as it provides a distinct gap between military and civilian vessels, particularly at larger sizes.  For one thing, the armor should be included in the hull structure.  For another, it provides a tradeoff between armor and speed, which turns Jackie Fisher's claim that "Speed is armor" on its head.  I guess my biggest problem is that instead of being a penalty on bigger ships, it's a sharp limit.  If you wish to build something at 60,000 tons (which I have done) it just won't go that fast no matter what.
A couple of other issues.  First, how is the limit measured?  This actually applies to all formulas.  Is it for the full-load mass, the empty mass, or the current mass?  For another, at low tech levels, a civilian ship will have absurdly low accelerations.  A "standard freighter" (the one outlined in the tutorial, or it's equivalent with 5 bays) is limited to around 1.8 m/s2 at the beginning.  That may be normal, or it may be a major headache.  However, the same ship at the end is limited to around 17.3 m/s2, which seems a little high for a civilian ship, but low for a military vessel. 
Just my opinion, but I would include armor thickness as well, which would allow more flexibility for the player in determining the capabilities of his vessel.

For some reason I was reading the formula as G rather than m/s2 , which of course makes the limits about 10x higher

I'll read the original post bearing that in mind.

Steve

[TheDeadlyShoe]

Hull Reinforcement
next to the existing
Armor

Hull reinforcement could scale off armor tech as well as its own tech?

[Yonder]

I second Byron that there should be some way that the player can design the ship in order to squeeze a little bit of speed out for the same amount of mass. Maybe in addition to "Armor" there could be a second "Internal Bulkhead" category? Multiple levels of this would mass much heavier than Armor though, because Armor is for the surface area, but Bulkheads are for the whole volume of the ship.

Then maybe the ship's number of 'Internal Bulkheads', in addition to increasing the maximum acceleration, adds to the HTK of every component or something like that.