Capital Missile weight

[marauder648]

How heavy are the missiles themselves?  It don't say in Sarna but IIRC they get super heavy with the Killer Whale being somewhere in the order of 50 tons per missile right?

[Liam's Ghost]

Barracuda: 30 tons
White Shark: 40 tons
Killer Whale: 50 tons
Kraken: 100 tons

[marcussmythe]

And at 20 damage apiece, an aerospace fighter can offen survive getting hit by its own mass in capital missiles, possibly several times over!

[Weirdo]

The main utility of capital missiles lies not just in their anti-fighter usage, but the insane flexibility provided by off-axis shots and bearings-only fire, allowing you to fire from behind cover, or use them as a kind of space artillery, with theoretically infinite range.

(The range is nice, but my favorite use of bearings-only shots is to get short or medium range to-hit numbers against targets at long or extreme range. Once you get beyond that, it becomes hard to predict a given unit's movement well enough to pull this off, forcing you to extend the missile's sensor setting, or just aiming for general flight path of a battle group.)

[Alsadius]

The main utility of capital missiles lies not just in their anti-fighter usage, but the insane flexibility provided by off-axis shots and bearings-only fire, allowing you to fire from behind cover, or use them as a kind of space artillery, with theoretically infinite range.

(The range is nice, but my favorite use of bearings-only shots is to get short or medium range to-hit numbers against targets at long or extreme range. Once you get beyond that, it becomes hard to predict a given unit's movement well enough to pull this off, forcing you to extend the missile's sensor setting, or just aiming for general flight path of a battle group.)

Unless you're this guy. (Not Battletech, but it's one of my favourite gaming stories ever. Doubly so when you read the comments and realize that for especially long shots it wasn't just about the accuracy of the character's shots - the player had to accurately guess the movement of the enemies too.)

Also, re capital missiles, the other big benefit to them is automatic TAC rolls. Not such a big deal at normal sizes where you can get threshold crits with typical guns, but against a monster like a Leviathan the ability to potentially lame it without needing to pound it into rubble first is really useful.

[marcussmythe]

The main utility of capital missiles lies not just in their anti-fighter usage, but the insane flexibility provided by off-axis shots and bearings-only fire, allowing you to fire from behind cover, or use them as a kind of space artillery, with theoretically infinite range.

(The range is nice, but my favorite use of bearings-only shots is to get short or medium range to-hit numbers against targets at long or extreme range. Once you get beyond that, it becomes hard to predict a given unit's movement well enough to pull this off, forcing you to extend the missile's sensor setting, or just aiming for general flight path of a battle group.)

Much of this depends on target agility.  We are watching in an AU Naval Design Campaign, run by the inimitable Alsadius, the proliferation of space based fixed defenses. While they provide phenomenal bang for their buck, I have some concerns about their future survival in the face of (hypothetical, as yet unbuilt, because the technology for bearings only launches does not yet exist) BCGs and BBGs, sending missile fire into the short range basket against immobile targets from beyond range of any reprisal.

Now, the flip of that is 'Fixed defenses work best as a force multiplier for, not a replacement for, mobile units'

[Weirdo]

What do you mean by the technology not existing? By definition, ALL capital missiles can do that. I'm even 99% sure that Sub-Caps can as well. Are you saying that in your setting, capital missiles haven't been developed yet?

[Alsadius]

I wanted to have tech growth take place over time, so I modified introduction dates slightly to smooth everything out. In the setting cap missiles exist, and they can do off-axis launches, but the tech for bearings-only launches doesn't exist as of yet. We're only in 2370 and vehicle-scale weapons still top out at the AC/5, so there's a lot of tech progression yet to come.

Yes, this is not quite canon, but it seemed more interesting this way. The joys of posts that happen in the Fan Rules section...

[cray]

And at 20 damage apiece, an aerospace fighter can offen survive getting hit by its own mass in capital missiles, possibly several times over!

They're not hit directly by missiles, but their bursting kinetic kill warheads.

[Daryk]

Marcussmythe, you just need to invest in point defenses.  Machine gun ammo (and AMS when it becomes available) is vastly cheaper than any capital missile.  Photons (i.e., Small Lasers) are even cheaper.  Yes, there are arc limits for weapons, but think about deploying multiple units to a single hex.  The fire control necessary for point defense weapons is trivial on space station scales...

[I am Belch II]

The firepower of the missles for their size is so horribly off.

[HobbesHurlbut]

The firepower of the missles for their size is so horribly off.

compared to the "magical" armor and incredibly powerful ECM in the BT 'verse?

[Liam's Ghost]

The firepower of the missles for their size is so horribly off.

I assume most of that mass is fuel. They aren't exactly costly enough that you'd expect them having a fusion plant.

[Retry]

I assume most of that mass is fuel. They aren't exactly costly enough that you'd expect them having a fusion plant.

...Fusion missiles as an alternative ammo type?

[dragonkid11]

...Fusion missiles as an alternative ammo type?

Each missile would cost million but considering the sheer price of a warship, you would think even the 'Go big and go big' SLDF would consider this too.

[VhenRa]

Congrats, I believe you just reinvented the adcap and sidearm from that old fan-project...

[dragonkid11]

Actually, now that I reread the rule. I can suddenly see why people in-universe would still use conventional chemical rocket for the Barracuda.

From the Strategic Ops, when using bearing only mode, the Barracuda could still be launched at 50 space hexes per minutes, which of course means that they have an unparalleled acceleration of 25 G.

I don't think there's any fusion powered craft that can go that fast. So even if Barracuda has barely enough fuel to burn for minutes compared to a fusion craft which can burn for hours or even days, you don't exactly need that range for a fight. And that acceleration would help against evading AMS (Which well... didn't do much and that probably spelled the end for fusion powered missile)

Seriously though, I would like to know what the heck kind of fuel the capital missile used to get such a ridiculous acceleration.

[cray]

From the Strategic Ops, when using bearing only mode, the Barracuda could still be launched at 50 space hexes per minutes, which of course means that they have an unparalleled acceleration of 25 G.

25Gs are nice, but there's room for higher acceleration in missiles. The 1970s Sprint comes to mind: 0 to Mach 10 in 5 seconds. The Sprint sustained 100Gs.
Sprint Missile
Sprint Missile Guidance Section

Seriously though, I would like to know what the heck kind of fuel the capital missile used to get such a ridiculous acceleration.

Simple, low specific impulse gunpowder can generate tens of thousands of Gs of acceleration in projectiles.

The important rocketry question is, "What's a capital missile's total delta-V?" Typical range is 50 hexes, 900km, and it crosses those in less than 60 seconds. That calls for a moderately impressive 15km/s, minimum, which is what you could expect out of a 3- or 4-stage hydrogen/oxygen, 50-ton-ish rocket pushing a warhead of under a ton. Since:
1) hydrogen & oxygen are pains to store, and
2) solid fuel isn't going to give more than 7-9km/s in that rocket size (for more than an LRM-sized warhead), and
3) You might need a lot more than 15km/s to cross a capital missile's Extreme range within 1 turn,

Then capital missiles might have some cheap, disposable fusion rocket to get sufficient delta-V.

[Alsadius]

If I had to spitball a solution, I'd say the capital launchers are railguns that give the missile a good starting kick, and they have fairly efficient chemical rockets.

The stats aren't actually crazy - for a rocket that gets an Isp of 400 seconds(well within practical chemical rocketry ranges, especially in a vacuum), you can get a payload of 654kg up to a speed of 15 km/s in a Barracuda-sized missile. If the railgun gives you 3 km/s of that, you can get 1405kg of payload instead. Some of that will be sensors, structure, rocket motor, etc., of course, so it's not like you're delivering a ton and a half of explosives. But a NAC/10 shoots a 200kg warhead to do 5x the damage of a Barracuda, and that 200kg seemingly includes propellant, so you don't need all that much of it to be the bursting charge.

Edit: Numbers from here: http://www.quantumg.net/rocketeq.html - dv is the added speed, isp is the rocket's efficiency(for reference, the best chemical-rocket lab firing I've ever heard of was 542s, and the best real-world rocket motor I know of gets 452s), m0 is the mass at the time of firing, and m1 is the mass after propellant is used up. I haven't played around with staging calculations yet.

For reference, the extreme case with Battletech rules(a 2.5M-ton WarShip using strategic fuel use of 39.52 tons/day to acccelerate at 1g) implies a rocket efficiency of about 5.5 trillion seconds.

[cray]

Ooo, crunchy numbers.

[marcussmythe]

My lack of math is showing... but to get that kind of performance, how fast is the exhaust travelling?  Other than ‘really, really, really fast’.  I get that part.  :)

[Liam's Ghost]

Then capital missiles might have some cheap, disposable fusion rocket to get sufficient delta-V.

Oooh, tiny little protium fusion orion drive?

[Liam's Ghost]

Congrats, I believe you just reinvented the adcap and sidearm from that old fan-project...

They really need to be reinvented. Those original versions I made were ridiculous.  :D

[Alsadius]

For the WarShip? If you use simple Newtonian calculations, about 54 trillion m/s, or about 180,000 times the speed of light. Naturally, that's quite impossible under Einsteinean relativity, so we have to get into advanced math.

It's been a long time since I've done this, but I think the easiest way is to use conservation of momentum, and say that the momentum of the 39.52 tons of fuel equals the momentum of the 2,499,960.48 tons of remaining spacecraft. The ship is moving at 846,720 m/s, so it has a momentum of 2.12x10^15 kg*m/s. The fuel thus has 5.36x10^10 kg*m/s of momentum per kilogram. So for 1kg we get E^2 = (pc)^2 + (Mo*c^2)^2 = 2.58x10^38 + 8.1x10^33 = 2.58x10^38 (the original mass-energy is irrelevantly small). E is thus the square root, or 1.61x10^19 J per kg of original mass. Substituting that into E=mc^2, that means 1kg of original mass now has a mass of 178.5kg. Substituting that into the equation for the Lorentz factor, we get 178.5 = 1/sqrt(1- v^2/c^2), which means sqrt(1- v^2/c^2) = 1/178.5, and then 1-v^2/c^2 = (1/178.5)^2, so 1-(1/178.5)^2 = 0.999969 = v^2/c^2, so v=0.999984c.

Simple, really.

[Weirdo]

Oooh, tiny little protium fusion orion drive?

I am NOT serving on a ship that's going to have multiple Orion drives pointed directly at it at close range on a regular basis... :o

[marcussmythe]

Simple.

"You keep using that word.  I do no think it means what you think it means." -Inigo Montoya.  :)

Yeah, I had figured the exhaust would have to be experiencing a relativistic mass increase - I got as far as 'this exhaust would have to be travelling faster than light, which it isnt' and my math left me there.

[Alsadius]

"You keep using that word.  I do no think it means what you think it means." -Inigo Montoya.  :)

Yeah, I had figured the exhaust would have to be experiencing a relativistic mass increase - I got as far as 'this exhaust would have to be travelling faster than light, which it isnt' and my math left me there.

Oh, did I leave the little  >:D emoticon out of the original? How careless of me.

Seriously, there's a good chance that my own math left at a large fraction of light speed as well, somewhere within that block of equations. But even if it's not spot-on, it's somewhere in the right vein.

As a side note, the maximum amount of energy that you can possibly get from a given mass of fuel is the fuel's rest mass-energy. So any equation that results in a higher energy in the exhaust's momentum than the rest mass is impossible without an external energy source(which WarShips do not have). Given that the engines are fusion, you're further limited by the theoretical efficiency of hydrogen fusion, which seems to be around 2.2% mass-to-energy conversion. So instead of the energy being 17,950% of the rest mass, you should only get 102.2%. Doing the numbers on paper, because it's too much of a pain to type them out, the ship should actually be using about 3,350 tons per day assuming its drive is a perfectly efficient fusion engine.

This actually makes me a bit sad, because this is something that is well within the realm of plausibility if BT used different construction and fuel consumption rules. Heck, it's not even all that far from what you'd get if the ship just used tactical fuel consumption(2 points per turn * 1440 turns per day / 2.5 points per ton = 1152 tons per day), especially once you get into more normal-sized ships - that's spot-on for a 860,000 ton ship like the Cameron. We could have had something accurately based on real-world math and physics simply by jiggling mass fractions a bit, if anyone had thought to do these calculations when they first made AeroTech.  :(

[Maingunnery]

As a side note, the maximum amount of energy that you can possibly get from a given mass of fuel is the fuel's rest mass-energy. So any equation that results in a higher energy in the exhaust's momentum than the rest mass is impossible without an external energy source(which WarShips do not have).

I blame KF interactions in the WarShip powerplant.  ;)

[marcussmythe]

Well, do we even know that the ‘fuel’ listed is the ejected reaction mass?  Of course even if the fuel is also the remass, we dont get there.

Im with Maingunnery on this.  Something magical is going on.  Some kind of handwaving.  Some energy source outside ‘mere’ perfect matter to energy conversion.

We -know- that some kind of magic is involved with the K-F drive.  (Note here by magic I mean ‘sufficiently advanced science and technology’.  Heck, K-F came out of ‘Hmm thats wierd’ with fusion powerplants, and we already know that battletech fusion powerplants themselves defy what we consider possible.

As a case in point on K-F ‘Magic’...  if a solar sail that small can charge a K-F core in that timeframe, they can charge a K-F core in the same timeframe out of the power that is goong into the ships normal, everyday hotel loads.. and certainly without burning so many tons of hydrogen in fusion.  Ergo, something is magical about the collected photons, something thats outside science as we know it - because fuel consumption and charge time and solar irradiance per unit area are facts, and do not require a theory.  They just are.

[Alsadius]

Well yes, I am well aware that fictional universes do not need to obey terrestrial physics. I checked out the news a couple times in 2012, and didn't see any stories about the Second Soviet Civil War at all(#fakenews #wakeupsheeple #https://xkcd.com/1013/). But when they can obey RL physics, I prefer that they do, because it makes reasoning inside the universe easier.

Edit: The rules to implement this are actually dirt-simple, too. WarShips are always in multiples of 10,000 tons. Each 1/10,000 of the WarShip's mass you invest in fuel gives you 200 fuel points. Fuel points are always spent at the tactical rate(so 120 pts/hour to maintain 1g). Likewise, DropShips are in multiples of 100 tons, so they get 20,000 points of fuel per 1/100 of the ship's mass that they put into fuel tanks. And that's it, you're done. Theoretical perfect efficiency is ~216 points per unit of fuel, so 200 per is a reasonable measure for a good high-efficiency fusion engine. The construction rules are simple, and you don't need to track "strategic fuel burn per day" with weird tonnage rates - every ship capable of useful interplanetary travel uses fuel at exactly the same rate in this system.

Again, I'm actually making myself a bit sad here. :/