[WH40K]The Cobra Class Length and Mass

[Lunacy1]

Rouge Trader gives very useful and consistent statistical information on ship sizes masses and lengths, mostly of which i agree with (barring kiloton capital grade weaponry - as apposed to rows and rows of thousands of guns in that range with capital grade being fewer, larger, and more powerful by one to two orders of magnitude).

Regardless my post is in regard to the size and mass given for the Cobra, that is 1.5km length and 5.7 million tons. Given this size the destroyer is on par with the sword class frigate for size (only one hundred meters shorter) and three hundred thousand tons lighter, but with far greater acceleration.
Due to their comparable size and mass calculations involving them often lead to the cobra class destroyer having comparable or superior power output to the sword class frigate.

Is their evidence for cobras being smaller than this size, me myself believe they should be significantly "lesser" than the sword in mass and power, given the supposed difference in class.

Would you consider the cobra to be 0.75km (model scale), or indeed the 1.5km length provided... given the ships role and class?
Everything i know of 40k tells me it would not be the latter

[Simon_Jester]

This thread should be labeled "40K Rogue Trader" or something.

[Thanas]

Added WH tags.

[Ahriman238]

1.5 Km for a Cobra is consistent with the ships length as given in Battlefleet Gothic.

[Eleventh Century Remnant]

5.7 million tons is very light for anything that size though- unless aerogel is a major structural component, and I can't quite see it fitting the grimdark ethos, they should be vastly heavier than that.

A 5.7 million ton cube of water would be only 178 metres on a side- closer in size to a guncutter (or a Tau Manta) than a Destroyer of His Divine Majesty's Fleet.

Making a couple of guesses about the configuration of a Cobra- that it is basically slightly taller than it is broad, witha length to draft of about 4:1 and a length to beam of about 5:1 (underneath all the spiky bits, that is)- you're looking at something upwards of a hundred million tons, probably around a hundred and sixty million, for a ship that has enough internal void spaces to more or less be able to float.

If it is significantly more heavily armoured than that, it'll mass more heavily than that also.

Roue trader does seem to lowball a lot of the sizes; I was calculating and writing on the basis of 2-3km frigates, 4-6km light cruisers, 5-8km cruisers, 9-11km battlecruisers and grand cruisers, 12-15km battleships, with the masses and damage tolerance those figures imply, on the basis of previous arguments about Battlefleet Gothic.

Accelerations, too, are disturbingly low- tremendously respectable by real world standards, but leading to week and month long insystem journeys that fit some fluff sources but not others, which imply much higher speeds, into the tens of 'g'.

[Sinewmire]

Yeah, I think some guys from this forum, when Rogue Trader was released, actually wrote to FInal Flight to ask if they'd intended Imperial ships to have the density of styrofoam, and the answer was "Yes, Imperial ships use very strong, very lightweight materials" or, as I read it, "No, but we're not going to reprint everything just for that".

[Cykeisme]

For a logical estimate of ship masses to their published sizes, what would be a reasonable number to multiply the published masses by? Say, a factor of 25?

[Lunacy1]

Someone did indeed write a letter to Final Flight and they explained that it was their intent for ships to have said masses - interstellar craft also have mass reduction (not very much talked about/of-course not understood but it exists), and ballistic based weapons such as macro - cannons use contra field generators so that when the shell exit's the gun into space, it retains an apparent mass lesser than the true mass, allowing for far higher speeds with the same energy, increasing range and power.

Given the canon mass of cruisers they could still have power output in the xe+20w range, (i dont believe ships engines literally burn with the power of the sun) or that weapons are in the teraton/petaton range for normal capital grade weapons. Given the power output extrapolated from RT, it would be consistent with their gigaton level firepower.
A reasonable multiplication of the published masses (assuming non-super light materials) and no mass reduction, you would likely want a factor of 100 or so.

I have always used the week to cross a solar system as something of a rule-of-thumb for imperial ships, it is spoke of in fluff although of course there are outliers! When ships come out of the warp, they must do so out side of the gravitational effects of planets, near the edge of the system, and then commence the journey to the desired world, taking hours-maybe, days, weeks, or in the case of some races possibly months. The single digit gravities are consistent with this.

Looking at Battlefleet Gothic and the provided speeds over 30 minutes, also reveals single digit accelerations being used for Imperial ships, even with references to full thrust in places.

Tens of G I do however agree with, cruisers have millions of tons of fuel, each ton one thousand times greater in energy density than conventional fusion. Five million tons of plasma fuel would allow a cruiser to maintain power outputs of xe+20W and single digit accelerations for months (months being the operational time of cruisers before refuel). Note however single digit accelerations are their "sustainable" acceleration, as we know from the same source, they can maintain these accelerations for at least weeks, but more likely months.

For lesser periods of time, at higher strain to the ships engines and superstructure however, ships can push their acceleration past this, into the double-digit G's possibly more.

WHat im saying is the weapon yields, plasma energy densities, single digit accelerations, and multi-month patrols of cruisers all form a consistent picture - one that i personally work with. I know others disagree with this however, believing petaton/exaton figures to be the norm, but i find this far more ill-consistent to the setting tbh.


so every body is happy that a cobra and sword are around the same size and mass, and destroyers and frigates differ not in scale or power output but instead only in role? I dont have a problem with this, only i always imagined cobras/destroyers simply being lesser in scale and power (like the model scale suggests) but it does not have* to be so. Irrc cobras have severely downgraded armor (feet thick), and likely pumps most of its power into engines, whilest the frigates have more normal, multi-meter thick armour and hence slower acceleration but with more guns/endurance. The extra three hundred thousand tons of mass in the sword, would have to be that extra armour

[Connor MacLeod]

I'm a bit curious what people think are 'accurate' ship masses, as well as the assumptions going into that. I know I have my own numbers, but I want to see what other people are basign their justifications on.

[Ted C]

I got to talk to the developers when Battlefleet Gothic came out (I was a GW Outrider back then), and my understanding is that the model scale is 1cm=1km. The board/map scale is much different, something like 1cm=1000km.

That puts the Cobra destroyers at around 2km in length, the Sword frigates a little longer, cruisers at 4-6km, and battleships at 8-10km.

[Eleventh Century Remnant]

"Mass lightening" in this context has the sound of a desperate ass- pull about it, and I wouldn't take it at all seriously positively. It means that they don't have the faintest idea how much things ought to mass, got the numbers pathetically wrong, and tried to weasel out by invoking a technology from another franchise, more than that one that comes with a hell of a lot of baggage, spin- off applications, implications, and physical ramifications that are nowhere else seen in the technical repertoire of the Imperium.

(Mass Lightening itself being a spin off from the subspace technology that makes Star Trek warp drive function, and we can be absolutely damn' certain the Imperium doesn't have that.)

It's a stupidly lazy and arguably plagiaristic (maybe too strong- plagiaresque?) attempt at a fix for a problem that being stupidly lazy caused in the first place. As a solution it's hardly worth pissing on.

A more complicated solution than borrowed magic may create more interesting consequences; I don't doubt that during the Dark Age of Technology the human race reached heights of materials technology that we would probably consider outright fantasy, through titaniridite, crystaliron and buckminsterfullerene up to and including physical members reinforced by fields of nuclear binding energy, or the field alone- but how much of that remains?

When it comes to lost technology, I do believe some things have gone- but they're these things way the hell out on the technical frontier, the things that were probably too advanced to be worth encoding in the STC system as there were only a handful of worlds that could do them anyway. Most ships have descended to and settled at the level of science at which they are routinely repaired and refitted, and for most that's not massively far beyond modern day, and most of the ultra- tech has probably migrated to where it can do the most good- structural members, reactor linings, engine bells, like that. (Largely guesswork.)

Mass probably varies from individual ship to individual ship; a major fleet yard where they work in iridium honeycombs filled with shear thickening gel layered with plates of thermal- ceramic and crystalline-aligned depleted uranium is going to produce a far lighter and tougher ship than a barely functioning outpost where they just melt down the nearest nickel- iron asteroid and slab it on.

Imperium drives are, I reckon, magnetoplasmadynamic- http://en.wikipedia.org/wiki/Magnetopla ... c_thruster- high speed, high mass flow, masively high power input, fits pretty well.

On the whole, I don't think most Imperium ships would float in water. Too heavily built, too much designed to sustain wear and abuse from their own crew as well as the enemy. Average density greater than 1- but probably not as high as 2, there are a lot of cavernous voids in there after all. I also think they'd likely vary a lot more one from another, even nominally of the same class, than you could really replicate on the scale of a game like Battlefleet Gothic.

happy with gigatons ship to ship, planetary bombardment as an ordnance task.

[Simon_Jester]

Personally I don't really believe in linear range scales in these games.

Look at the tabletop version of ground combat- maximum ballistic range of a heavy artillery piece is what, 240"? Compare that to effective pistol range: 12." It's not really credible that 40k pistols are accurate out to 5% of the range of large-caliber artillery; in real life it's more like 0.2%. And effective sword range on the tabletop is 1/6 of effective pistol range, too...

So I just figure that adding a distance increment on the tabletop corresponds to multiplying the distance by a factor of e or whatever.

[Brother-Captain Gaius]

Look at the tabletop version of ground combat- maximum ballistic range of a heavy artillery piece is what, 240"? Compare that to effective pistol range: 12." It's not really credible that 40k pistols are accurate out to 5% of the range of large-caliber artillery; in real life it's more like 0.2%. And effective sword range on the tabletop is 1/6 of effective pistol range, too...

Well, strictly speaking, an Earthshaker gun is light field artillery, not heavy, and certainly not large calibre by any relative measurement...

[Simon_Jester]

Oh, don't be pedantic.

If you want, I could make things look even sillier- what's the maximum range of a Deathstrike Missile? What ICBM only outranges a pistol by a factor of... forty, I believe?

[Darth Hoth]

"Mass lightening" in this context has the sound of a desperate ass- pull about it, and I wouldn't take it at all seriously positively. It means that they don't have the faintest idea how much things ought to mass, got the numbers pathetically wrong, and tried to weasel out by invoking a technology from another franchise, more than that one that comes with a hell of a lot of baggage, spin- off applications, implications, and physical ramifications that are nowhere else seen in the technical repertoire of the Imperium.

(Mass Lightening itself being a spin off from the subspace technology that makes Star Trek warp drive function, and we can be absolutely damn' certain the Imperium doesn't have that.)

It's a stupidly lazy and arguably plagiaristic (maybe too strong- plagiaresque?) attempt at a fix for a problem that being stupidly lazy caused in the first place. As a solution it's hardly worth pissing on.

Mass-lightening predates Star Trek, though. Or at least technobabble that reduces or cancels out inertial mass does.

Then again, many franchises these days seem to be using some kind of mass/inertia trickery. Stargate did, and so did Mass Effect, Andromeda, some of the SW EU . . . So if the Warhammer guys are being derivative, they are by no means alone. (These other franchises also tend not to consider the implications of the tech, obviously enough.)

[Eleventh Century Remnant]

Inertialess drive does, certainly, but as far as the Lensman series goes, the most prominent place I know it from, that's another fictional technology in itself with a whole range of consequences, spin- offs and implications again.

I'm trying to think of anywhere else I can remember it, mass lightening or inertialessness, coming up in the range of thirties-through-sixties sci- fi, I'm sure somebody must have chanced on the physical possibility, but nothing prominent comes to mind. I'm probably missing something really obvious- if you know better, do tell.

(Whether the two amount to the same thing- or are related- interesting question. There's at least one fringe physics advanced propulsion scheme, that I have used in not-yet-fleshed-out stories that, depends on the unproven theory that the physical phenomenon of inertia is actually caused by the quantum- level effects of gravity.)

We're talking about fictional technologies anyway, I'm much more annoyed about the shabby copypasta-ism of the writing and storytelling, of the vast amount of incuriosity and not thinking it through that involved.


Edit add- the Necrons use "inertialess drive", which sounds like it was supposed to be a homage to Doc Smith, but has a different set of physical properties again; the necron connection actually makes it slightly more likely, unless the Thing Under Cydonia has been retconned again.

[Lunacy1]

I'm a bit curious what people think are 'accurate' ship masses, as well as the assumptions going into that. I know I have my own numbers, but I want to see what other people are basign their justifications on.

Well ignoring official weights, and barring mass-reduction, ild estimate 3.6 billion tons for the lunar given its length of 5 Km and and point twenty five solidity
so 128 times heavier than the canon figure.

-the multi-megaton mass thing with the single digit acceleration (for what they can maintain for weeks+) does work out quite well for ships operational times and plasma energy densities though?
-there are 2 (iirc possibly 3) references to the mass reduction in fluff though, besides the given masses
-the fact it exists in other sci-fi is irrelevant i think

[Connor MacLeod]

Yeah, I think some guys from this forum, when Rogue Trader was released, actually wrote to FInal Flight to ask if they'd intended Imperial ships to have the density of styrofoam, and the answer was "Yes, Imperial ships use very strong, very lightweight materials" or, as I read it, "No, but we're not going to reprint everything just for that".

Yes

[Connor MacLeod]

Rouge Trader gives very useful and consistent statistical information on ship sizes masses and lengths, mostly of which i agree with (barring kiloton capital grade weaponry - as apposed to rows and rows of thousands of guns in that range with capital grade being fewer, larger, and more powerful by one to two orders of magnitude).

The nature and composition of broadside, direct fire weapons mounts (macro cannon, etc.) is not uniform. This includes number of guns and the size of the guns and the shells they throw, and there are tradeoffs to either end of the scale.

Regardless my post is in regard to the size and mass given for the Cobra, that is 1.5km length and 5.7 million tons. Given this size the destroyer is on par with the sword class frigate for size (only one hundred meters shorter) and three hundred thousand tons lighter, but with far greater acceleration.
Due to their comparable size and mass calculations involving them often lead to the cobra class destroyer having comparable or superior power output to the sword class frigate.

Is their evidence for cobras being smaller than this size, me myself believe they should be significantly "lesser" than the sword in mass and power, given the supposed difference in class.

Smaller ships have existed. A 500 m rapid strike vessel in Angels of darkness, and Graham McNeill implying some 'few hundred meter' raider in Iron Warrior IIRC, but Graham has been known to go his own way on things before and may not be considered a 'standard'. There might be a km long raider in other sources, but then again Execution Hour also gives Raiders a mere 100,000 ton mass so...

Beyond that, nothing I am directly aware of ever suggests a Cobra is significantly smaller than a frigate. They're both escorts, and by role the main difference is that destroyers are dedicated recon and torpedo platforms, while frigates are multi-role (they pack direct fire weapons instead of ordnance). Power output figures based on mass and acceleration can be problematic, because you need to have an idea of exhaust velocity and the amount of propellant expelled for a given amount of thrust We know 40K starships are basically of the 'magical fusion torch' variety but that still doesn't tell us much of what we need to know.

It also depends on the relationship between reactor power and various systems. Engines may be able to draw more power than guns or shields can (depending on design.) - it's not neccesarily all 'equal' the way it is assumed to be in other universes (like Star Wars)

Would you consider the cobra to be 0.75km (model scale), or indeed the 1.5km length provided... given the ships role and class?
Everything i know of 40k tells me it would not be the latter

Artwork and game models should be treated with a massive grain of salt since there can be logical problems with their design. EG for example, lance turrets are hundreds of metres long/wide by ship scalings (depending on the size of starship you use) yet you're supposed to be able to rotate the turret in some ships by work crews using chains. OR on the ground side of things, there are massive consistency problems with the design of the Leman Russ (gun calibre and ammo size, turret size, etc.)

For that matter most of the weapons and armor tend to be grossly out of proportion IMHO as well (particularly bolters and space marine armour, but even lasguns are probably bulkier than they actually are or need to be, just because that seems to be some 40K asthetic.)

given all that I'd be very careful about what you use model scalings (and artwork) for things. Although starship artwork is probably more consistent than most.

Someone did indeed write a letter to Final Flight and they explained that it was their intent for ships to have said masses - interstellar craft also have mass reduction (not very much talked about/of-course not understood but it exists), and ballistic based weapons such as macro - cannons use contra field generators so that when the shell exit's the gun into space, it retains an apparent mass lesser than the true mass, allowing for far higher speeds with the same energy, increasing range and power.

The only source EVER to mention 'mass reduction' was Barrington J Bayley's 'Eye of Terror' and the nature and function was not very explicit. It was onyl mentioned to be used to reduce the thrust needed to lift ships up to orbit. Further, given the only technologies that are 'mass reducing' - Eg Suspensors and related tech, do not literally reduce mass, it is debatable that they do much of anything.

I have certainly never heard of 'contra field generators' using mass lightening on macro cannons. sounds like someone is copying Andromeda or Mass Effect and applying it to 40K.

Given the canon mass of cruisers they could still have power output in the xe+20w range, (i dont believe ships engines literally burn with the power of the sun) or that weapons are in the teraton/petaton range for normal capital grade weapons. Given the power output extrapolated from RT, it would be consistent with their gigaton level firepower.

What 'canon' mass are you talking about? The FFG ones? What are the propellant/exhaust velocity figures that you are using?

Also 'power of the sun' depends entirely on what kind of star you are talking about, since stars vary in luminosity (power output) rather dramatically. Assuming 'sun/star' means 'our sun/star' is wrong (which I have point of fact assumed in the past.) Besides which, if you start upping the mass (or accel) figures, the power outputs for the starships will correspondingly grow unless you play some games with propellant and exhaust velocity.

A reasonable multiplication of the published masses (assuming non-super light materials) and no mass reduction, you would likely want a factor of 100 or so.

Why?

I have always used the week to cross a solar system as something of a rule-of-thumb for imperial ships, it is spoke of in fluff although of course there are outliers! When ships come out of the warp, they must do so out side of the gravitational effects of planets, near the edge of the system, and then commence the journey to the desired world, taking hours-maybe, days, weeks, or in the case of some races possibly months. The single digit gravities are consistent with this.

The exact distances and emergence points can vary dramatically. Closest 'safe' is 2.3 million km (Savage ScarS) although only skilled Navigators and/or high tech starships can do that (Inquisition basically.) Otherwise implied emergence points can be as little as tens of millions of km (Eye of Terror, again) but more usually seem to be within 1 AU or more. Billions of km is not uncommon, but seems to be more of a 'safe bet' emergence point than anything, and prboably dictates the usual emergence point for commercial/civilian traffic (chartist ships, etc.)

And of course some races like the Orks have emerged closer (10 Planetary diameters in Rynn's World) albeit not without catastrophic losses.

Travel time will also be dictated more by the ship's velocity (limited by fuel and/or propellant requirements) and the type of engine they have. I doubt starships routinely blast across the system at max power settings unless they actually need to, especially merchant vessels.

Looking at Battlefleet Gothic and the provided speeds over 30 minutes, also reveals single digit accelerations being used for Imperial ships, even with references to full thrust in places.

Er what? Are you trying to do accel figures off the BFG gameplay?

Tens of G I do however agree with, cruisers have millions of tons of fuel, each ton one thousand times greater in energy density than conventional fusion. Five million tons of plasma fuel would allow a cruiser to maintain power outputs of xe+20W and single digit accelerations for months (months being the operational time of cruisers before refuel). Note however single digit accelerations are their "sustainable" acceleration, as we know from the same source, they can maintain these accelerations for at least weeks, but more likely months.

Based off what? I'm well aware of where the 1000x energy density thing comes from (I've made such assumptiosn before) but it's a bit context dependent, and I've never heard any mention of how much fuel starships actually carry.

For lesser periods of time, at higher strain to the ships engines and superstructure however, ships can push their acceleration past this, into the double-digit G's possibly more.

WHat im saying is the weapon yields, plasma energy densities, single digit accelerations, and multi-month patrols of cruisers all form a consistent picture - one that i personally work with. I know others disagree with this however, believing petaton/exaton figures to be the norm, but i find this far more ill-consistent to the setting tbh.

That's one possible interpretation, but as I recall the vast majority of people (here and elsewhere) typically went with gigaton/teraton range figures for 40K ships (firepower, et al.) with petaton reserved for rare things like certain kinds of nova cannons (which also have long refire rates that could translate into long recharge rates.) Indeed the only person on this board I can ever recall seriously arguing petatons was myself, and that was long before the FFG Rogue Trader material came out, nevermind that its years later and my own ideas have changed since then.

Well ignoring official weights, and barring mass-reduction, ild estimate 3.6 billion tons for the lunar given its length of 5 Km and and point twenty five solidity so 128 times heavier than the canon figure.

What assumptions were you using for this mass?

-the multi-megaton mass thing with the single digit acceleration (for what they can maintain for weeks+) does work out quite well for ships operational times and plasma energy densities though?

Again that depends on your parameters as I've oulined before. You can play around with numbers to get petawatt scale outputs for starships, for example (albeit geared more towards the high end of the scale) if propellant use is high and a significant proportion of said mass is propellant) and that would mesh with 'terawatt' level weapons, 'terajoule las broadsides', lances that can vape a square km of water (well a body of water), or 'kiloton' macro cannon shells. By one interpretation, at least.

-there are 2 (iirc possibly 3) references to the mass reduction in fluff though, besides the given masses
-the fact it exists in other sci-fi is irrelevant i think

Two references to mass reduction (Space fleet and Eye of Terror) but the former implied it was rare and likened it to a suspensor, and the latter was purely in context of ships lifting off from orbit.

This is contradicted by other examples: EG in BFG they need scores of men to haul a multi-ton macro cannon shell into the breach. Mass lightening should make loading and firing the guns (hell torpedoes and nova cannon too) than is typically displayed and yet... Plus there is that whole 'we dont know how 40K mass reducing actually works.'

[Connor MacLeod]

5.7 million tons is very light for anything that size though- unless aerogel is a major structural component, and I can't quite see it fitting the grimdark ethos, they should be vastly heavier than that.

A 5.7 million ton cube of water would be only 178 metres on a side- closer in size to a guncutter (or a Tau Manta) than a Destroyer of His Divine Majesty's Fleet.

Depends on the density figures you go with. 5.7 million tons (an APPROXIMATE figure, mind, so let's not go treating it as an absolute precision number.) is not far off the tonnages for Honorverse starships post 'great resizing', and they used an average density of IIRC 250 kg*m^3 which isn't far off some estimated figures from Atomic Rockets.

Making a couple of guesses about the configuration of a Cobra- that it is basically slightly taller than it is broad, witha length to draft of about 4:1 and a length to beam of about 5:1 (underneath all the spiky bits, that is)- you're looking at something upwards of a hundred million tons, probably around a hundred and sixty million, for a ship that has enough internal void spaces to more or less be able to float.

If it is significantly more heavily armoured than that, it'll mass more heavily than that also.

What assumptions about hull thickness are you assuming, exactly? Hull thicknesses can range from 'metres' (the smallest precise figure I recall being 5 metres from Emperor's Mercy) to scores of metres thick (for a Grand Cruiser from Black Crusade Core rulles, IIRC.) A Mars class battlecruiser had 15 m thick armour as per Wolf's Honour, and FFG mentioned a cruiser in Battlefleet Koronous having 10 m thick hull (the Ambition cruiser, I think.) Those could skew mass figures, depending on how extensive the armoring is.

Roue trader does seem to lowball a lot of the sizes; I was calculating and writing on the basis of 2-3km frigates, 4-6km light cruisers, 5-8km cruisers, 9-11km battlecruisers and grand cruisers, 12-15km battleships, with the masses and damage tolerance those figures imply, on the basis of previous arguments about Battlefleet Gothic.

It varies according to author. Battleships (or battle barges) have gotten as small as 5-6 km or 'several km' (Andy Hoare, Anthony Reynolds, Jonathan Green), whilst on the other end they can be 10+ km long (or more)2 Escorts have ranged from hundreds of metres to 4 km (as per Know No Fear and Dan Abnett) and Cruisers have ranged from 2-8 km (not including battlecruisers or grand cruisers, which up that to 9-12 km) not including the 30km outlier for the Macharius from a Rennie short story.

Accelerations, too, are disturbingly low- tremendously respectable by real world standards, but leading to week and month long insystem journeys that fit some fluff sources but not others, which imply much higher speeds, into the tens of 'g'.

Transit times across systems depend on the emergence point from the warp (which can vary with ship, navigator and system) as well as other factors. For example, we know some starships can accelerate up to a velocity before entering warp, or may exit warp at a high velocity (I believe the infamous 'Sabbat Martyr .75c velocity' example had the ship dropping out of the warp at that speed, as did the Phalanx in 'Flight of the Eisenstein.')

"Mass lightening" in this context has the sound of a desperate ass- pull about it, and I wouldn't take it at all seriously positively. It means that they don't have the faintest idea how much things ought to mass, got the numbers pathetically wrong, and tried to weasel out by invoking a technology from another franchise, more than that one that comes with a hell of a lot of baggage, spin- off applications, implications, and physical ramifications that are nowhere else seen in the technical repertoire of the Imperium.

(Mass Lightening itself being a spin off from the subspace technology that makes Star Trek warp drive function, and we can be absolutely damn' certain the Imperium doesn't have that.)

It's a stupidly lazy and arguably plagiaristic (maybe too strong- plagiaresque?) attempt at a fix for a problem that being stupidly lazy caused in the first place. As a solution it's hardly worth pissing on.

Again we don't know what the mass lightening does or how it works.. Not everything works like how the purported STar Trek 'mass lightening' is supposed to work (I'm no longer sure I even believe it does that.) and different universes/authors have had their different approaches (mass effect, Andromeda, and Revelation Space are all examples.)

Nevermind that we don't know if the mass reducing affects all the attributes of mass (EG matter, inertial mass, gravitational mass, etc.) or if it can play around with the individual attributes (EG affect gravitational and/or inertial mass without affecting matter.) or what. We know precisely DICK about how it operates, and the best guesses I've got on the matter suggest it does not, in fact, literally reduce mass (EG suspensors) - its more antigravity crap.

A more complicated solution than borrowed magic may create more interesting consequences; I don't doubt that during the Dark Age of Technology the human race reached heights of materials technology that we would probably consider outright fantasy, through titaniridite, crystaliron and buckminsterfullerene up to and including physical members reinforced by fields of nuclear binding energy, or the field alone- but how much of that remains?

It's 40K. 'enchanted metal' is not really that big a stretch of the imagination considering it is possible to 'create' stable, psychically created materials (eldar Wraithbone). hell it occurs spontaneously (waystones, and I'm pretty sure there's other examples of the warp taking tangible form in realspace.) it doesn't stretch the imagination that it can affect/enhance other mateirals, even mundane iron (most Daemon engines take advantage of this property to compensate for the fact they incorporate shit like brass and iron into their construction. OR daemons in squishy organic bodies being drmatically tougher than squishy organic bodies ought to be.)

That doesn't rule out 'high tech sci fi super materials' either (some 40K authors seem to like that kinda stuff) but its not the only option here and its not exactly implausible for the setting either. It's not as if you can just ignore the existence of what amounts to magic in 40K (but being 'magic' does not make it totally arbitrary, either.)

Imperium drives are, I reckon, magnetoplasmadynamic- http://en.wikipedia.org/wiki/Magnetopla ... c_thruster- high speed, high mass flow, masively high power input, fits pretty well.

Why do you figure that 'fits' better than other potential drive options?

[Lunacy1]

The nature and composition of broadside, direct fire weapons mounts (macro cannon, etc.) is not uniform. This includes number of guns and the size of the guns and the shells they throw, and there are tradeoffs to either end of the scale.

I know, this is shown in the artwork within the books, and BFG

I have certainly never heard of 'contra field generators' using mass lightening on macro cannons. sounds like someone is copying Andromeda or Mass Effect and applying it to 40K.

I found this image on the internet, I dont have the source at hand it so it could be fan art, I haven't looked deeply enough into it. It suggests the use of contra fiel generators to reduce apparent mass of macro shells (after they leave the ship) so they can achieve the multi-thousand km/speeds
http://imageshack.us/photo/my-images/81 ... efirs.png/

What 'canon' mass are you talking about? The FFG ones? What are the propellant/exhaust velocity figures that you are using?

Yes the FFG ones, and light speed

The reason I said a factor of one hundred, is because of the approximate>3 billion mass estimate I mentioned, over one hundred times the given canon mass. I retract that comment though, it was a quick response, the masses do not go up linearly by volume, and the factor would be different for the different classes. But for cruisers 100x seems reasonable no?

Travel time will also be dictated more by the ship's velocity (limited by fuel and/or propellant requirements) and the type of engine they have. I doubt starships routinely blast across the system at max power settings unless they actually need to, especially merchant vessels.

This is why I said I believe the single digit "sustainable" accelerations are the ones that can be maintained for at least weeks, whilst higher accelerations can be achieved for shorter periods of time.

Er what? Are you trying to do access figures off the BFG gameplay?

Only as a sort of secondary supportive source — iirc the speed in RT over the turn of 30 minutes is actually consistent with their own given accelerations (speeds which are faster than BFG assuming comparable turn length) however all ahead full where ships go to full thrust in BFG can theoretically get into the double digit G range, and speeds can be increased through game mechanics in RT each. I would not use game mechanics as a stand alone source of course xD.

Based off what? I'm well aware of where the 1000x energy density thing comes from (I've made such assumption before) but it's a bit context dependent, and I've never heard any mention of how much fuel starships actually carry.

Well i used best theoretical results expected from fusion to come to an upper limit, and as for fuel I have come across two although not for cruisers. Space-fleet iirc and Rouge Trader state the Goliath at the end of a trip lasting up to two years will have several million tons of fuel! 1-2 sources for that. Also RT continues, there is enough fuel to blow of a planets atmosphere, now this puts the energy density for each ton of fuel at the stated 1000x fusion thing (within an order of magnitude). So over the course of ~months the cruiser would have produced that energy equivalent, possibly more (it is a cruise not a frigate, but the Goliath is a mass carrier designed to refine and transport plasma, so they could be comparable in the mass of fuel carried).
I feel this is relatively consistent with the multi megaton masses and G accelerations though i sense not many agree): :L

[Lunacy1]

That's one possible interpretation, but as I recall the vast majority of people (here and elsewhere) typically went with gigaton/teraton range figures for 40K ships (firepower, et al.) with petaton reserved for rare things like certain kinds of nova cannons (which also have long refire rates that could translate into long recharge rates.) Indeed the only person on this board I can ever recall seriously arguing petatons was myself, and that was long before the FFG Rogue Trader material came out, nevermind that its years later and my own ideas have changed since then.

Fair enough, I read several forums the petaton/exaton thing is taken seriously on Factpile or at least it used to be, i dont read up there any more... I found it a poor source of information.
Well i think single-double digit gigatons is the norm for cruisers, with certain very heavy weapons getting into the hundreds-thousands of gigatons, whilst remaining below certain benchmarks (as to not destroy almost all life in shorter time frames than Exterminates and generally remaining below the teraton range to that end, and because of a lance like energy beam with teratons of energy capable of vaporizing several trillion tons of rock is inclined to be beyond the capability of ordinary Imperial lance armed ships (Shadow Point). I think if cruisers can consistently put out teratons, then they would destroy planets populations to fast in relation to dedicated WMD's for said role.

I have searched the internet for the quote but could not find it, however somewhere in the collection of Warhammer books in my room is a passage describing the yield of torpedoes used by a strike cruiser (30k iirc). The yield of these weapons was 3 gigatons. The scale of Imp torpedoes likely means a far higher yield, in the same magnitude.

[the atom]

It varies according to author. Battleships (or battle barges) have gotten as small as 5-6 km or 'several km' (Andy Hoare, Anthony Reynolds, Jonathan Green), whilst on the other end they can be 10+ km long (or more)2 Escorts have ranged from hundreds of metres to 4 km (as per Know No Fear and Dan Abnett) and Cruisers have ranged from 2-8 km (not including battlecruisers or grand cruisers, which up that to 9-12 km) not including the 30km outlier for the Macharius from a Rennie short story.

In Ghostmaker I believe Abnett talked about 20km sizes for larger ships.Truth be told I find I'm actually coming up on the 5km frigates/escorts and 20km cruiser/battleship sizes much more often then the 1km and 5km sizes (though I'll be damned if I can remember exactly where...).

[Connor MacLeod]

I found this image on the internet, I dont have the source at hand it so it could be fan art, I haven't looked deeply enough into it. It suggests the use of contra fiel generators to reduce apparent mass of macro shells (after they leave the ship) so they can achieve the multi-thousand km/speeds
http://imageshack.us/photo/my-images/81 ... hefirs.png

I've seen that online too, but I dont know where it comes from. As a rule of thumb if I dont know where it comes from and if someone whose opinion I trust (EG white Rabbit or black admiral for example) can't identify it for me I don't believe it. I've had too many leads turn out to be false or messed up due to hearsay or forum/wiki opinion or shit I found on the internet.

Besides which, while some of it I can kinda agree with (implied thousands of km/s velocity for shells, which you kind of need to strike at tens or hundreds of thousands of km) the ranges are a bit goofy (half an hour for an unguided shell to reach a target? Not likely!)

Yes the FFG ones, and light speed

I'm not sure you can just assume 'near-c' covers exhaust velocity. For one thing, it really amps up the numbers and if you're trying to avoid TERATONS or petatons (esp if you want to amp up the ship masses) you need to cut back on exhaust velocity as much as you can, given velocity contributes far more to KE than mass. As a rule of thumb I've been going more along the lines of thousands/tens of thousands of km/s, that leads to some not so insane propellant requirements, and it can kind of be justified based on estimated plasma cannon velocities (starship or ground based.)

The reason I said a factor of one hundred, is because of the approximate>3 billion mass estimate I mentioned, over one hundred times the given canon mass. I retract that comment though, it was a quick response, the masses do not go up linearly by volume, and the factor would be different for the different classes. But for cruisers 100x seems reasonable no?

It depends on the parameters you're using. Cruisers for example range between 3 km and 8 km, and the hull thicknesses (as I noted) vary greatly. If we were talking 10+ meters average hull thickness, then yes, a few billion tons (assuming an iron density or thereabouts) is not terribly unreasonable as an estimate. If you stick with thinner hull thicknesses (EG 5 meters as per Emperor's Mercy) then it probably won't be nearly that massive. And then there's always hull densities (what if the density of the magic metals is closer to aluminum or titanium rather than iron or tungsten?)

This is why I said I believe the single digit "sustainable" accelerations are the ones that can be maintained for at least weeks, whilst higher accelerations can be achieved for shorter periods of time.

In context I was trying to also point out cases where a ship might spend a small part of its time accelerating, spend most of the time coasting through the system at a given velocity, then only slow down (not neccesarily stop) when it reaches the edge of the system. A ship that could (for example) pull 50 gees could spend 5-6 hours accelerating up to around 10,000 km/s or so and then spend the bulk of that time crossing the system with engines idle.

Only as a sort of secondary supportive source — iirc the speed in RT over the turn of 30 minutes is actually consistent with their own given accelerations (speeds which are faster than BFG assuming comparable turn length) however all ahead full where ships go to full thrust in BFG can theoretically get into the double digit G range, and speeds can be increased through game mechanics in RT each. I would not use game mechanics as a stand alone source of course xD.

The problem with game mechanics is that its extremely abstracted. Andy Chambers gave some rough ideas for the BFG game as far as times and distances go, but they weren't meant to ever be taken as absolute gospel (even though people do in fact treat them as absolutes.) For example, during the half hour how do you treat a ship's movement? Is it moving EXACTLY in a straight line unwaveringly, or does it slow down, adjust course, etc. or perform any other sorts of manuvers. Does firing during a turn represent a single broadside, or a sustainrd barrage of multiple broadsides over that period of time? And so on and so forth.

Well i used best theoretical results expected from fusion to come to an upper limit, and as for fuel I have come across two although not for cruisers. Space-fleet iirc and Rouge Trader state the Goliath at the end of a trip lasting up to two years will have several million tons of fuel! 1-2 sources for that.

space fleet indicated 'conventional nuclear fuels' as I recall it, which can mean anything from fission to antimatter. It also doesn't specify the efficiencies of the reaction (not all fusion reactions are alike as I recall on atomic rockets) so its open for debate. Not to mention the not-so-minor probelm of explaining how one kg of fuel can break E=MC^2 without throwing physics out the window (which is a whole lot of mental gymnastics to go through, so the justification better be pretty damn solid.)

Also RT continues, there is enough fuel to blow of a planets atmosphere, now this puts the energy density for each ton of fuel at the stated 1000x fusion thing (within an order of magnitude). So over the course of ~months the cruiser would have produced that energy equivalent, possibly more (it is a cruise not a frigate, but the Goliath is a mass carrier designed to refine and transport plasma, so they could be comparable in the mass of fuel carried).

That depends on how you defined the exact quantity of fuel the Goliath carries. As well as the hwole 'break E=MC^2' thing. I'm pretty sure someone would try to argue that the calc depends on the atmosphere of the planet involved (and might then go to argue its a really thin atmosphere.)

Fair enough, I read several forums the petaton/exaton thing is taken seriously on Factpile or at least it used to be, i dont read up there any more... I found it a poor source of information.

Petatons could depend on the weapon or the ship. Some of the bigger battleships (which can get pretty big) and the fortress monasteries like Phalanx probably could manage at least petaton range. Exaton range.. dunno. Rare stuff maybe like Phalanx.

Certain exterminatus munitions like Cyclonics could also get up into the petaton range, as can nova cannon (potentially), and both can be used in a ship to ship role in at least a few sources. Alot of it can hinge on interpretations and how you're trying to balance all the examples (both low end and high end).

Well i think single-double digit gigatons is the norm for cruisers, with certain very heavy weapons getting into the hundreds-thousands of gigatons, whilst remaining below certain benchmarks (as to not destroy almost all life in shorter time frames than Exterminates and generally remaining below the teraton range to that end, and because of a lance like energy beam with teratons of energy capable of vaporizing several trillion tons of rock is inclined to be beyond the capability of ordinary Imperial lance armed ships (Shadow Point). I think if cruisers can consistently put out teratons, then they would destroy planets populations to fast in relation to dedicated WMD's for said role.

Destroying all life on a planet isn't really going to be much of a benchmark, given that they can and do employ viral weaponry and probably have other means. Likewise, it depends on the kind of world (depopulating an agri world or a research colony is going to be easier than one where the populace is belowground.) It's also going to vary based on context - Some forms of Chaos, as well as particularily persisent xenos with microscopic forms (Orks, Tyranids, and Necrons) probably require considerably greater energies to sterilize the planet (which is going to be orders of magnitude more than simply wiping out all life on the planet.)

Besides which, one of the big things arguing FOR teraton range firepower is going to be greater masses and accelerations. A 5 km cruiser massing billions of tons with tens or hundreds of gee max accel is going to be pumping out energies well into the teraton range over any appreciable timeframe. Nevermind things like nova cannons, or macro cannon (Depending on estimated mass and velocities and payloads) and such. hell we know from BFG and more than a few other sources that lances, fusion torpedoes and mass drivers all constitute methods of exterminatus as well, and those all represent starship weaponry.

I have searched the internet for the quote but could not find it, however somewhere in the collection of Warhammer books in my room is a passage describing the yield of torpedoes used by a strike cruiser (30k iirc). The yield of these weapons was 3 gigatons. The scale of Imp torpedoes likely means a far higher yield, in the same magnitude.

The only obvious 'gigaton' I ever heard of were the Space Hulk 1st edition hulk killer nukes (112 5 gigaton nuclear warheads, 100 which of each were carried by a battlecruiser.) Other novels have gone with 12 megaton warheads (Deliverance lost), 36 20-megaton directed yield assassin mineds (Imperial armour IX-X), and the Atlas Class ground bobmardment missile which is a megaton yield as well (how many we don't know), but its designed to take out reinforced targets and titans. OH and then there's the usual megaton range tactical bombardments (codexes dealing with hive fleet behemoth and the Battle of macragge, planetstrike, etc.)

[Simon_Jester]

It depends on the parameters you're using. Cruisers for example range between 3 km and 8 km, and the hull thicknesses (as I noted) vary greatly. If we were talking 10+ meters average hull thickness, then yes, a few billion tons (assuming an iron density or thereabouts) is not terribly unreasonable as an estimate. If you stick with thinner hull thicknesses (EG 5 meters as per Emperor's Mercy) then it probably won't be nearly that massive. And then there's always hull densities (what if the density of the magic metals is closer to aluminum or titanium rather than iron or tungsten?)

Regarding size ranges- one thing that occurs to me is that some cruisers may be much boxier, with a higher width-to-length ratio than others. For example, some of the big 'cruisers' have those big nova cannon: those sound like long-barreled axial weapons, and you may need a long, spindly hull to build the nova gun into the keel of the ship. The long narrow hull also favors bow-on engagements, because it means you present a much smaller target to the enemy. And you can save mass on your main armor belt by putting it perpendicular to the axis of the ship, like the gun shield on an artillery piece.

(It doesn't have to stick out like a gun shield, it can just be a solid "pie plate" of armor that separates the expendable stuff near the front end of the ship from the important stuff near the back, built into the hull where you can't easily see it).

Whereas something designed to launch broadside barrages of torpedo and what Battlefleet: Gothic models as "weapons" or "lance" fire might well be built shorter but with a fatter hull, so that it can wrap more defensive depth of armor and shielding and expendable spaces (like crew quarters and fuel bunkers) around the core hull.

In context I was trying to also point out cases where a ship might spend a small part of its time accelerating, spend most of the time coasting through the system at a given velocity, then only slow down (not neccesarily stop) when it reaches the edge of the system. A ship that could (for example) pull 50 gees could spend 5-6 hours accelerating up to around 10,000 km/s or so and then spend the bulk of that time crossing the system with engines idle.

This actually makes a lot of sense if life support and routine sensor watch use less energy than firing up the main engine. We normally think of high-power SF drives as being continuous boost, but there's no logical reason to do that if it doesn't pay.

For a continuous-boost spaceship with high accelerations, adding an extra hour of engine burn time gives you diminishing returns in saved travel time. The first hour gives you a fixed travel time, say 60 days. The second hour gives you a travel time of 30 days (one half that). The third gives you 20 days (one third), and so on.

So does it make sense to burn the engines for another hour, taking off component lifetime and "expending a prodigious amount of the Emperor's fuel," just to save five days of trip time?

It might not, under a variety of conditions. Say, if you aren't confident of being able to refuel and your tanks are low. Or if you might have to fight a very energetic and dangerous battle at the end of your mission. Or if this is a routine redeployment of troops or ships and you aren't in any real hurry to get things done. Or you aren't totally sure of how long your century-old most Omnissiah-blessed rocket engines will hold up under a continuous 50g burn and don't want to risk blowing a gasket before your next scheduled maintenance stop.

So maybe 120 hours in transit is a smarter option than spending 1 hour burning the engines at top acceleration. Unless you're in a hurry.

Besides which, one of the big things arguing FOR teraton range firepower is going to be greater masses and accelerations. A 5 km cruiser massing billions of tons with tens or hundreds of gee max accel is going to be pumping out energies well into the teraton range over any appreciable timeframe. Nevermind things like nova cannons, or macro cannon (Depending on estimated mass and velocities and payloads) and such. hell we know from BFG and more than a few other sources that lances, fusion torpedoes and mass drivers all constitute methods of exterminatus as well, and those all represent starship weaponry.

Of course, there's a great difference between sustained barrage and individual weapon capability.

At the Somme, the British fired off roughly one and three quarter million artillery shells, easily translating to a few thousand tons of explosives. This does not mean they managed to do as much damage to the German lines as a couple of low-yield tactical nuclear warheads would have done.

The same comparison might lend itself to a seven-day bombardment from shipboard energy weapons, versus a few shots from something like a nova cannon.