Effective Combat Range in Space

[doom3607]

Regretfully, even at the 1000c the drives can do going to resupply would necessitate a supply base effectively in whatever system you're fighting in, otherwise it would take days to get there and back, not counting time to reload. But that might work, I'll wait for further feedback. At any rate it's something I didn't consider.

And for the last time, it's not "anywhere to almost anywhere" it's "almost anywhere to anywhere, but inaccurately"!

[Purple]

And for the last time, it's not "anywhere to almost anywhere" it's "almost anywhere to anywhere, but inaccurately"!

It's the same thing really. 1000km is nothing, assuming your ship can achieve escape velocity (11.2 km/s) your ship will cover that distance in about a minute and a half. With the kind of firepower and ranges you are talking about that is trivial.

[doom3607]

No, I mean in the sense that he seems to believe you can jump out of gravity wells, but not in. It's the other way around.

[Dwelf]

No, I mean in the sense that he seems to believe you can jump out of gravity wells, but not in. It's the other way around.

No you mentioned that you can't jump out so I left it at that. The almost anywhere was a reference to the inaccuracy of the drives. I could probably have phrased that better but there you have it.

bah fixed my spelling

[Terralthra]

Unless you're launching your missiles by shoving them out the back of your ship with the BEEFCAKE MUSCLE POWAH of your sweaty crewpersons, you're going to have the same problem with what to do with the waste heat produced by launching them.

Pssst. Pressurized gas or springs don't have heat management problems. After the thing is at a few dozen meters it ignites its engines and goes where it must go.

Good sir, the laws of thermodynamics are not tramps. You must at least buy them dinner before violating them.

1st Law violation: Springs and pressurized gas do not generate energy; they are essentially batteries, storing energy in a way that is easy to release as kinetic energy. Even if you use them, they still must get the energy from somewhere, and that energy generation method will produce waste heat, because of the 2nd law of thermodynamics.

2nd Law violation: Springs and pressurized gas do, in fact, generate waste heat. Compressing a spring and a gas produces heat as a byproduct of friction. Always. You don't detect this when you compress a spring in your hand because the amount of energy is miniscule and your hand isn't a good detector of heat on that scale. That doesn't mean it isn't there, and when you're talking about enough energy to move KKVs around en masse, that amount will get rather non-miniscule rather quickly.

[Simon_Jester]

Eh.

You can probably manage missile launch racks without causing unacceptable waste heat problems- the amount of energy required to get the missile going at ~10 m/s just to get it out of the ship isn't really that extreme, especially if it's done by mechanical means that are (relatively) energy-efficient such as hydraulics.

At that point you've got more work on your hands handling the waste heat from the engines than from the launch system.

Of course, this increases the danger that the missiles will be destroyed by random fire in the space immediately around your ship before it can light off its main drive.

[Connor MacLeod]

So instead of dumping missiles out of the ship, dump some sort of standoff weapon system or disposable weapons pod/directed warhead(again a bit more like Revelation space) There's a couple ways you could do that depending on how your tech works.

[Beowulf]

2nd Law violation: Springs and pressurized gas do, in fact, generate waste heat. Compressing a spring and a gas produces heat as a byproduct of friction. Always. You don't detect this when you compress a spring in your hand because the amount of energy is miniscule and your hand isn't a good detector of heat on that scale. That doesn't mean it isn't there, and when you're talking about enough energy to move KKVs around en masse, that amount will get rather non-miniscule rather quickly.

A cold gas thruster would not, in fact, generate waste heat. Due to adiabatic expansion, the pressurized gas would have a lower temperature as exhaust, than when it started, resulting in the gas thruster removing heat. This almost certainly will be greater heat removal than is added by friction, resulting in a decrease in heat overall (assuming that the pressurized gas is created well before battle begin).

[Simon_Jester]

If the pod is armored enough, this works, or can work. But at a certain point you have to ask: why not simply take these missile pods, mount a drive on them, and make them independent warships in their own right?

There are always going to be physical factors that lead to diminishing returns in construction of warships past a certain size- you can do it, but the strain on your engineering establishment is high, there will be a lot of unresolved bugs, and the ship won't perform as well as its tonnage might lead you to think it will relative to a host of smaller ships.

[Terralthra]

2nd Law violation: Springs and pressurized gas do, in fact, generate waste heat. Compressing a spring and a gas produces heat as a byproduct of friction. Always. You don't detect this when you compress a spring in your hand because the amount of energy is miniscule and your hand isn't a good detector of heat on that scale. That doesn't mean it isn't there, and when you're talking about enough energy to move KKVs around en masse, that amount will get rather non-miniscule rather quickly.

A cold gas thruster would not, in fact, generate waste heat. Due to adiabatic expansion, the pressurized gas would have a lower temperature as exhaust, than when it started, resulting in the gas thruster removing heat. This almost certainly will be greater heat removal than is added by friction, resulting in a decrease in heat overall (assuming that the pressurized gas is created well before battle begin).

Why are you saying that as if you're contradicting me? I said compressing the gas would generate waste heat. Nothing you've said contradicts that. Indeed, by saying that allowing the gas to expand would remove heat, you're agreeing with me that compressing it adds heat by default. If the gas is pressurized well before combat, that limits the throw weight of the ship to whatever gas storage is, in addition to whatever missiles are actually being launched.

[someone_else]

Problem one: Engine plumes really aren't very good armor, period. They may damage incoming projectiles, but by the time said projectile gets close enough that the damage starts piling up at a useful rate, the projectile no longer really needs to be guided- so burning off its targeting radar or telemetry receivers doesn't do you a lot of good. And vaporizing it, if the thing is well designed, is pretty much out of the question.

It's not the engine plume proper (that is going to be not particularly dense anyway), but the IR/visible radiation from the reaction chamber. I'll show you why its engine is a good defense.
You say this thing weights 10 billion tons (omyfuckinggod! ), and doom said the engines in his setting give accelerations in the 1-5 gravities scale.
The engine's thrust power is Fp = (F * Ve ) / 2 (courtesy of Atomic rockets)
F is thrust and Ve is exhaust velocity.

F= m*a = 10'000'000'000'000 kg * 3*9.81 = 294'300'000'000'000 newtons.

Ve is very high, in the 200-300 km/s range since this is a fusion torch expelling plasma (hell, even VASIMR can reach Ve of around 300 km/s). Let's say 250 km/s.

Fp = (294'300'000'000'000 newtons * 250'000 m/s) /2 = 3,67875 E+19 Watts, or 36'787'500 Terawatts or 36.79 Exawatt.

Now, to put it in context, the total solar irradiance on the whole Earth surface is 130 or so Petawatts (or 0.13 exawatt), this is a 9-gigaton-bomb going off per second into your reaction chamber.

This assumes a 100% efficient torch, where the whole reaction energy is directed in thrust power. Given that it's rarely the case, you are looking at at least the same amount of energy escaping as IR and visual radiations (for a 50% efficient torch).

Since you'll likely want your reaction chamber to be like Daedalus's (a bowl that is both the reaction chamber and the nozzle), you are shining half that in the direction of the enemy. Half shines at you. So be prepared.

When you find something that can withstand these levels of irradiation and remain a solid, give me a call.

By the inverse-square law, at 1000 km from the engine there are still P/(4*3.14*r) = 36'787'500 TW/(4*3.14*1'000'000) = 2.93 TW/m2
Still too much for a KKV, and any solid slug will be significantly ablated and recoil away.

Btw, this also points out how murderously difficult is to reject the insane amounts of waste heat from torch drives.

At this scale and performance, Kzinti lesson is pretty much law.

I wind up with clouds of little mini-impactors going all over the place in the kilometers immediately surrounding the ship.

This is a not-so-smart tactic, since fragments aren't optimized for penetration (anyway, how big those fragments are? I see them as thumb-sized or less and you say are "mini"), and will be stopped by relatively simple whipple shields that I can install on KKVs. If instead of wasting your mass like this you shoot rod-like projectiles, you get through whipple shields much more easily. But the area you cover gets smaller.

Or it can fire off small multi-KKV armored boosting stages that will then deploy the KKVs after they get clear of this mincemeat.

The same problem arises if I have efficient laser or particle beam weapons, which can be detuned to deliver a 'wash' of light or charged particles surrounding your ship- continuously, with no gaps to make it easy to launch KKVs in.

If you have so efficient beam weapons the whole design becomes a glorified KKV barge (an engine and little more) whose orders are to deploy huge amounts of KKVs at high speeds while it is well beyond the laser's range.

And at this point it should become far cheaper than the boatload of lasers you are using.

Good sir, the laws of thermodynamics are not tramps. You must at least buy them dinner before violating them.

I said "don't have heat management problems", not "they don't generate waste heat". I meant that the waste heat generated by springs or pumping gas to eject a missile are minuscule when compared to the heat management problems of a gun throwing a projectile at the same speed that the missile can boost it (after it is clear of the launching ship).
The former heat problem can be solved with passive cooling, the latter is unpractical or even impossible with modern tech.

And in any case, the work will be done when the KKV racks are reloaded, at the port, so who goddamn cares.

[doom3607]

I was actually thinking the missiles were less KKVs and more good old megaton-range fusion bombs.

And actually, Simon raised a good point about stuff being too light. If it makes it more reasonable, weight shall be increased by an order of magnitude! Fear my hundred billion ton warships! Hmm. This may wind up requiring even more suspension of disbelief than some of Star Trek... But still less than holes in event horizons.

And 36.79 exawatts for a ten-billion-ton abomination? Crap, now it's 367.9 exawatts!

Cold gas... I think I may go with using cold gas to shove missiles off the ship. Or, hell, since everyone on board would be bracing for wildly changing g-forces anyway I may just start spinning the ship and let the things roll off.

[Sky Captain]

What happens to ships that enter FTL at very high STL velocity? Do they exit at same velocity they enter? If so it is very easy to attack a planet if all you want is to wreck it. Just have dedicated kamikaze ship (basically huge missile with efficient STL engine and FTL drive) that attains high STL speed, then enters FTL and pops out of FTL few thousand km from planet while moving at some 10 000 - 20 000 km/s. Good luck stopping something like that without a planetary shield.

[doom3607]

Exactly. And yeah, you could do that, but why would you? This isn't Star Trek, there's not a habitable planet in every other system. The United States of Earth is a sphere about five hundred light years across. It contain eighty-three habitable worlds. if the world has a main defense facility, it makes more sense to just get a big ship into low orbit and use your engine on it.

[Simon_Jester]

I wind up with clouds of little mini-impactors going all over the place in the kilometers immediately surrounding the ship.

This is a not-so-smart tactic, since fragments aren't optimized for penetration (anyway, how big those fragments are? I see them as thumb-sized or less and you say are "mini"), and will be stopped by relatively simple whipple shields that I can install on KKVs. If instead of wasting your mass like this you shoot rod-like projectiles, you get through whipple shields much more easily. But the area you cover gets smaller.

Hmm. In answer to the question of fragment size, it depends on how energetic you think of a kinetic impactor as being, and how massive. I tend to think in terms of kilogram-range objects that can fragment into gram-range pieces, and in terms of relative speeds during the engagement of hundreds or thousands of kilometers per second. If not, the time scale of the battle becomes very large, which raises a whole different set of problems.

Firing very large numbers of rod-shaped penetrators out of large dispersed batteries of small, quick-firing mass drivers is also an option. I may have some of the engineering wrong here, but there is a critical point- when you've got people casually throwing around billions of tons of hardware and enormous volumes of energy, it actually is possible to saturate a (small) volume in space with intense radiation or large numbers of impactors and effectively deny that space to anything not well armored.

Or it can fire off small multi-KKV armored boosting stages that will then deploy the KKVs after they get clear of this mincemeat.

Noted earlier- you can do this, but at a certain point one begins to wonder why you bothered with the monitor in the first place. Is it anything but a large missile bus that carries the swarm of kinetic impactors? Why have only one such bus, instead of several smaller ones, with reduced risk of some isolated failure wrecking your whole offensive? If you're launching from such ranges that armor protection of your launch platform is largely irrelevant and saturating the space the impactors are expected to be launched through is impractical, what's the point of building a huge, heavily protected platform to do it on?

The same problem arises if I have efficient laser or particle beam weapons, which can be detuned to deliver a 'wash' of light or charged particles surrounding your ship- continuously, with no gaps to make it easy to launch KKVs in.

If you have so efficient beam weapons the whole design becomes a glorified KKV barge (an engine and little more) whose orders are to deploy huge amounts of KKVs at high speeds while it is well beyond the laser's range.

And at this point it should become far cheaper than the boatload of lasers you are using.

Deploy from that far out and you run into targeting problems, because the required intensity of laser/particle radiation is relatively low for this purpose: I'm not trying to melt meter-thick steel plates here. Sure, you can lob your impactors on ballistic trajectories from umpty million kilometers away, but your ability to line up your shots against the important targets of the engagement is in doubt under those conditions.

I was actually thinking the missiles were less KKVs and more good old megaton-range fusion bombs.

That is not necessarily a better idea. Fusion bombs are large and structurally fragile relative to a rock or a hunk of iron; there are many ways to damage a fusion bomb so that it will not create the desired explosion without having to destroy it outright, whereas to neutralize a kinetic impactor as a threat you pretty much have to melt large chunks of it- to knock it off course, if nothing else.

Now, there will be contexts in which a fusion-tipped missile honestly is the best weapon to use in space combat. But there are also plenty of cases where it isn't.

And actually, Simon raised a good point about stuff being too light. If it makes it more reasonable, weight shall be increased by an order of magnitude! Fear my hundred billion ton warships!

Er... why are you making the weight larger, instead of making the ship smaller? Would it somehow harm you to reduce the physical size of these ships you've dreamed up, scaling down to a reasonable size for their predetermined mass?

That's how Weber did it when he made the same mistake you did...

Also, you have not yet addressed the issue of what happens when this beastie runs into an alpha-strike missile launch from its own weight in smaller units. Due to surface area constraints it can't possibly throw as many missiles as quickly as said swarm of smaller units, so if ships have drives that allow them to teleport the hell away from a battle, it is going to get creamed, because the battle may only last a few minutes and in those minutes the monitor gets hit by, say, 10000000 nukes while only launching 10000 nukes of its own.

[someone_else]

I was actually thinking the missiles were less KKVs and more good old megaton-range fusion bombs.

The point is that to kill each missile you only need a tiny piece of crap, and nukes are expensive.

Besides, with your engines, getting up to relativistic speeds is a breeze. This calculator (that takes relativity in account, although calculates a full acceleration/deceleration trip so you have to halve the time and distance figures) can tell you how little time you need to do so. In around one month of steady 10 gees acceleration, traversing "only" 0.025 light years (1581 AUs), you have stuff going at 0.6 c, or 60% lightspeed.

I'm not going to calculate the mess 10 billion tons can do on a planet, at that speed.

Frankly, I'd advise to place some restrictions on the engine performance (say it has "combat thrust" and "voyage thrust", with the former being in the gees and the latter in milligees, and say that the "combat thrust" uses loads of fuel so it's used only in combat), or you risk this going way out of hand.

Why have only one such bus, instead of several smaller ones, with reduced risk of some isolated failure wrecking your whole offensive?

The reason was what I proposed earlier, that engine performance does scales faster than engine size. So a Honking Big missile bus can carry much more payload than a swarm of vehicles of smaller sizes.

Also, the BIG engine provides an "umbrella" to keep enemy kinetics from approaching too much. Assuming it is shaped just as an hemisphere (otherwise it burns my KKV too and I don't want that), anything incoming at less than a very big distance from the hull is incinerated or deflected by the hellish heat, while its own KKVs have time to spread more before becoming a target. You can run the inverse square rule to see how big the umbrella really is.

I was trying to save the concept. I personally prefer cheap second-hand space transports as missile buses, and something much more sedate than this.

Hmm. In answer to the question of fragment size, it depends on how energetic you think of a kinetic impactor as being, and how massive.

I was thinking in the 50 kg range, and I have no fucking idea about the speed.
At beyond 50 km/s targeting them gets slightly complex. I mean, if they go at 100 Km/s in one second they traverse 100 km. In one second, even if their engine can push them at 100 gees around, they can move trasversally of only 492 meters (displacement =0.5*a*t*t).
They need much bigger sensors to home on target autonomously from this range, and they cannot be guided in the final run due to lag becoming a problem.

Sure, you can lob your impactors on ballistic trajectories from umpty million kilometers away, but your ability to line up your shots against the important targets of the engagement is in doubt under those conditions.

Nah, the main factor that influences KKV targeting them is their relative speed, not their distance (the distance does not even influence the number of the ones you can shoot down, since they are deployed from well beyond the laser range anyway). They can be remote-guided by spotters until the final run, and it's there that speed cuts both ways if it is too much.

[doom3607]

Wow, this is getting into a hell of a lesson on how not to make a warship. Right, what would make ships as I've described them viable? From the sound of it, some sort of 'jump point' network would help- that's fine, I can do that. And some sort of energy weapon for the bigger ships- fine, I can do that too. Maybe some sort of by-product of the FTL drive being the ability to make sort of a gravity wave gun or something? Or is that completely insane? Because something like that I can see as sort of a lightspeed space shotgun that utterly shreds little ships but takes fuckloads of power restricting it to big ship carrying it... Anything else?

[someone_else]

Somehow tangential to the thread, but I think this is still an appropriate read for you.

Battleships: a ridiculous but awesome idea

[doom3607]

I hereby declare that no torch drive can ever get a decent fusion reaction going and limit itself to surviveable gees for anything as light as a fighter. Or something. Screw carriers.

[Simon_Jester]

I hereby declare that no torch drive can ever get a decent fusion reaction going and limit itself to surviveable gees for anything as light as a fighter. Or something. Screw carriers.

...You just also screwed missiles rather effectively.

[Simon_Jester]

Ghetto Edit:

Someone_else, that article you linked to reminds me a bit of a Cracked.com article. Entertaining and with some insights, but not really adequately researched or thought out, suggesting someone whose knowledge of the subject is kind of superficial.

Taking it apart line by line would involve a bit more work than I'm interested in this evening, but suffice to say that he seems to have drawn some very broad, easy, facile conclusions about "the way history works" that ignore a lot of context and details. In particular, on the subject of the battleship, I am honestly suspicious that he hasn't made much study of some of the context in which battleships played a role.

One point is that in many cases battleships had a huge effect on the outcome of naval campaigns just by existing, because like it or not, a handful of destroyers or a cruiser a third of the battleship's size didn't have much chance of taking one on. Fast battleships could dart out of harbor, intercept a convoy or invasion fleet, and maul the shit out of it; this was a well known capability that entire campaigns would up planned around.

If you look at, say, the Allied attempts to get supplies through to Russia via the North Atlantic to help them against the Germans, you will note that one of the huge limiting factors was the risk that the German battleship Tirpitz would charge out of the harbor it occupied in Norway and maul the convoy, because it could outrun the freighters in the convoy. Such a disaster would do so much damage to the supply line that the convoys only dared to go around Norway at a great distance (to provide warning time if Tirpitz came out and attacked), and with battleship escort of their own (to even up the odds against Tirpitz). Air power could sink a battleship, yes, but only in good weather and daylight. Submarines could sink a battleship, but the submarines were so slow underwater they practically had to park in front of the battleship and hope it practically ran over them.

He talks about how "The torpedo boat probably would have done the same thing against the battleship had it been used properly. In fact, when it was, it did pretty well," which is blatant bullshit- how much good did torpedo boats do against battleships in, hell, anywhere? Aerial torpedoes yes, submarine torpedoes yes, but torpedo boat torpedoes never really accomplished that much against enemy capital ships. The torpedo boat was just too small and too slow a platform, an eggshell armed with a sledgehammer- certainly not something capable of "maneuver warfare" except under the most perfect of conditions against opposition whose feet are nailed to the floor, which is a common assumption made by people who make a fetish of maneuver at the expense of actual firepower.

Now, I could make more general comments about how the man seems to make a fetish out of maneuver warfare, missing the point that this is as much a strategic concept as a tactical one and that so very often the positional combat still matters; there is honestly not always a way to sneak around, outrun, outmaneuver, and elude the enemy so that you can kill him on the cheap.

But best to stick to battleships.

Edit to the Edit: anyone who wants to see more of what I have to say on the matter can go looking in the comment thread of that very post.

[doom3607]

I didn't say the gees weren't surviveable for the fighter. I'm just saying you can't get a fusion flame small enough to propel a small fighter with few enough gees to not kill a human.

[Simon_Jester]

I didn't say the gees weren't surviveable for the fighter. I'm just saying you can't get a fusion flame small enough to propel a small fighter with few enough gees to not kill a human.

Use an AI fighter. Save the weight of hauling eighty kilos of meat plus life support around.

[Dwelf]

I hereby declare that no torch drive can ever get a decent fusion reaction going and limit itself to surviveable gees for anything as light as a fighter. Or something. Screw carriers.

So you just upped the size of the thing the carrier carries. All hail frigate carriers that clears up 2x busses worth of space for more guns. In addition it speeds bringing them into the system up since you don't have 100 inaccurate vessels to transition but 1 inaccurate vessel.

[Sky Captain]

One purpose for huge multi billion ton space dreadnought would be to carry biggest most powerful gamma ray or x ray laser possible to attack stuff orbiting on predictable trajectory from ligh hours away although aiming the thing accurately would be difficult. But in this setting there is little need for such weapon because it is possible to jump in close proximity and spam missiles from few thousand km.