[Flaser]

Here are the Space Warfare musings and subsequent discussion posts from Rocketpunk manifesto.
If one were to hold a space warfare training, these would be *required* reading. Not only are the articles chock full of thoughtful ideas with multiple lot of well laid out scenarios for each argument, the discussions also tend to back up their stuff with maths and citations.

I: The Gravity Well
II: Stealth Reconsidered
III: 'Warships' in Space
IV: Mobility
V: Laser Weapons
VI: Kinetics, Part 1
VII: Kinetics, Part 2 - The Killer Bus
VIII: Orbital Combat
IX: Could Everything We Know Be Wrong?
X: Moving Targets
XI: La Zona Fronteriza
XII: Surface Warfare

Also ...

Battle of the Spherical War Cows: Purple v Green
Further Battles of the Spherical War Cows

And last but not least

Space Fighters, Not
Space Fighters, Reconsidered?

[headdie]

Some very interesting reading and defiantly a valuable resource for discussions like this and defiantly something to consider about when creating mods etc

[NGTM-1R]

something to consider about when creating mods etc

We have no interest in your "realism".

[headdie]

something to consider about when creating mods etc

We have no interest in your "realism".

I said consider not follow

[StarSlayer]

Realism

Yeah...

WAVE MOTION GUN!!!

[Nuke]

i still think gatling guns in space is the way to go, they just have to be recoilless gatling guns.

[watsisname]

Pfft, projectiles. Put me down for a freaking laser -- nothing screams cool like vaporizing your enemy with the power of PHOTONS.  That said, if Wave Motion Guns are allowable, sign me up for one of those.

[MR_T3D]

I think real space warfare would be lame, ****ing newton and Einstein.

[Flipside]

Thing is, Space combat could be anything from pitched battles in approximately Geostationary orbits to Frontieresque jousting at relative speeds of hundreds of kps, whilst you could effectively accelerate particles up to nearly the speed of light, I suspect most Space-borne weapons would be wave-based, not particle. Missiles, for example, would be pretty much useless unless you have a BSG type situation where ships were quite happy to remain effectively stationary and engage in a tiny area of an infinite combat theatre.

[Flaser]

Thing is, Space combat could be anything from pitched battles in approximately Geostationary orbits to Frontieresque jousting at relative speeds of hundreds of kps, whilst you could effectively accelerate particles up to nearly the speed of light, I suspect most Space-borne weapons would be wave-based, not particle. Missiles, for example, would be pretty much useless unless you have a BSG type situation where ships were quite happy to remain effectively stationary and engage in a tiny area of an infinite combat theatre.

Wave based? What are you smoking gent, I want some! If you meant light-speed, then... maybe.

Seriously missiles can accelerate just as well as a ship, and there's no reason why they couldn't intercept a ship. The same physical laws apply to both and the ship's also weighted down by a mission section and the delta-v requirement (huge fuel to mass ratio) to carry out its mission. Meanwhile the missile can be designed with a lower delta-v requirement and it won't have squishy humans inside with their bulky and heavy life support system.

Finally just put a bomb-pumped laser on the missile as a warhead and you've got one deadly weapon that can do a "proximity kill" in space from a light-second away. Even atomic warheads would need to get a lot closer (couple of kilometers) to do the deed with sheer gamma radiation pressure.

For sanity's sake: read the damn stuff people with engineering and science degrees have posted above. Especially the spherical war-cows stuff, as they debate kinetics-vs-lasers to kinetics-vs-lasers-vs-missiles to death in a myriad scenarious.

The correct answer is: "It depends". For mili-gee drives even ballistic kinetics are an issue, however for torch-drives they have so much power that only light-speed and missile weapons with a similar drive would be.

This isn't about far future tech with anti-matter or some gravity/quantum quirk that would allow a "reactionless" drive.

This is strictly plausible mid future tech. You've got miligee nuclear-electric drives (with Giga-Watts of power! ~ a current nuclear power-plant can do about 500-1000 MW!) on the low, pretty sure end and full-g torch drives (with Terra-Watts! of power) on the far power that also does some magic hand-waving about how a magnetic nozzle operates. Between the two are micro- to deci-gee direct nuclear drives, the big brother of NERVA.

Those are the drives with enough specific impulse to make interplanetary missions viable. So anything "realistic" will have to be based on those figures.

Space Battleship Yamato, Battlestar Galactica, Star Wars, Star Trek, Babylon 5, any goddamn sci-fi show is *BULL***** as far as hard realism and number crunching goes, especially since they use magitech like forcefields or just engines (like on the Vipers) that are beyond what is physically possible. If you don't like this, then stick to your fantasy...

...but don't mix the two.

[Flipside]

Yes, by wave based I mean Lasers and other Energy based weapons, and yes, I was talking about light speed, else I wouldn't have mentioned it was possible to some Particle Accelerators to reach those kinds of speeds as well.

And whilst a missile can accelerate just as well as a ship, how quickly can it do it, what happens if an object has been accelerating towards Earth using some kind of Ramjet, how quickly is a response to that going to be defined, is a missile going to be able to intersect or match speeds with something that has been accelerating for months?

In the situation you described, regardless of the mount, what is doing the damage, the missile or the weapon attached to it? The reason I pointed out the BSG scenario was because of the unlikelihood of it happening in a genuine space theatre, which was one of the reasons why missiles would be of limited use.

As for 'what I'm smoking', well, if you are going to drag the debate down there, there's no damn point having a discussion, it just turns into a thread on SpaceBattles.com

[Herra Tohtori]

I have found this thread. It can no longer hide from me.

That said, let the nitpickery commence.

"Fast" is in fact a bit of a slippery concept when it comes to spacecraft. Speed in space is all relative to begin with; the more useful measure for a spaceship is delta v,  "change in velocity" - especially, how much you can change your velocity before you run out of gas. For any given propulsion technology, the way to get more delta v isn't a more powerful engine but a bigger fuel tank. What a powerful engine does give you is higher acceleration - so you can achieve any given delta v more quickly.

This is, of course, wrong.

The delta v of any given space ship is not as simple as the writer assumes. Calculating the movement of a variable-mass system like space ship filled to brim with propellant is complex and annoying and time-consuming, so let's simplify the problem by looking at a short duration burn, where the mass of expended propellant is significantly less than the entire mass of the ship:

m << M


The mass of the propellant is given ejection velocity v_e, and the conservation of momentum assures that the ship gains equal but opposite momentum.

Now, the momentum given to the propellant mass is

p = mv_e

while the momentum that ship gains is

p = Mv


And conservation of momentum means that

mv_e = Mv

and solving the equation for the end velocity of the ship, we get

v = mv_e / M


From here, you can see the following statements can be made:

1. Increasing propellant mass expelled during the burn while keeping ejection velocity and ship mass constant will increase the end velocity v.

2. Increasing the ejection velocity of propellant while keeping other variables constant will increase the end velocity.

3. Reducing ship's mass and keeping engine parametres constant will increase the end velocity.


By now you should see the flaw in the reasoning in the quoted paragraph. "More powerful engine" does not only mean that it can dump bigger propellant mass per dt out into space, it can also mean that it can do it at higher ejection velocity, which is in fact the more important term for the efficiency of the engine.

Basically, the higher the ejection velocity, the less propellant you need for a given change of momentum (and velocity). Keeping your ship as light as possible will also help immensely, but as far as propulsion technology goes (as long as it's based on conservation of momentum), increasing the amount of propellant is much less efficient than increasing the ejection velocity.

EDIT: Of course, it could be that when the writer says "any given propulsion technology", he means to say that the ejection velocity is fixed or in the same order of magnitude; however I disagree with this sort of classification, because especially with electromagnetic engines you can increase the ejection velocity pretty much linearly, unlike with chemical rockets where you are limited by materials and the properties of the expanding gas and chemical energy available from reactions.

[Nuke]

i think the best bet for inter stellar drives would be long duration nuclear reactors generating power for drives that operate on the interstellar medium. not quite the fusion powered ramjets (which essentially use the ism as propellant, by collecting burning, and accelerating it out the tail pipe) that have been considered in the past. instead you just provide power to electromagnetic or electrostatic devices to change the velocity of particles in the ism. you wound need to operate on single atoms so the amount of volume contained by the whole acceleration system would need to be huge. without the need for propellant, you can maintain lightweight construction (a real engineering challenge considering the amount of volume to be considered). such a ship would likely have very slow acceleration, however the drive could operate for decades on a single fueling. il leave it up to the super-physicists in this thread to pick apart the idea.

[Flaser]

@Herra: that is a bit of a nitpicking, if you checked more of the articles then it will be abundant that the writers are *very* much aware that specific impulse (the speed at which propellant leaves the engine, divided by its mass) can have massive effects.

That's why most realistic designs use electric (ion, field-effect, etc.) engines since they have a massive isp.

You also made a not entirely correct assertion, as merely lowering the craft's mass (without changing any engine parameters) would include carrying less fuel, which we all know won't result in more delta-v. However if we amend, that lowering the mass of ship components beside fuel, then yes - it would produce more delta-v. However that's the very same thing as increasing the ship's fuel-to-mass ratio.

What the entry refers to is sticking a "bigger" engine on a craft. It will give more thrust, but isp for a given technology is set or at least won't scale that much with size... as a result you won't gain any (significant) delta-v, only the ability to accelerate, ergo reach your delta-v faster.

So to sum it up:
Delta-v is the result of your technology specific isp and your fuel fraction.
Acceleration is the result of your technology specific isp and the size of your engine.

@Nuke: why do you keep referring to nuclear drives as "ramjets"? Rockets are a specific technology, that is a (for pressure and other engineering considerations) combustion chamber with only a single outflow, whereas ramjets, like all jets also have an intake.

Granted propellant is pumped into a reactor in most nuclear designs, but these don't qualify as jets, since the energy of the propellant is independent of the speed of the craft compared to its medium. Ramjets are just a kind of jet, with no moving parts, and compression achieved by intake shaping. None of this applies to nuclear rockets.

What might confuse you, is the Bussard Ramjet, which travels at relativistic speeds and uses the sparse hydrogen in space as propellant. That is a very far-far future technology. What do you mean "operate on the interstellar medium"? If you mean a "collection system" like a Bussard Ram, and an ion drive that uses this as propellant, then there's no reason not to use a ramjet as otherwise you'd have to slow (from an inertial frame fixed to the spaceship, the propellant has a massive velocity) the propellant down before accelerating it again. You could combine an electric drive with the ram, by also accelerating the propellant with an electromagnetic field. In the end, these drives can only operate at significant fractions of lightspeed, so they're far ahead of what we've been discussing.

[Nuke]

as anyone who has watched cosmos at least once, ramjet, in space propulsion context, refers to a fusion powered spacecraft that uses the interstellar medium as a both fuel and propellant. its a very old concept that has been around since the 60s.

for the idea i proposed, the term ramjet works fine. it would have an intake, to bring in the interstellar medium, but rather than burning it if a fusion reactor like the bussard ramjet, you really just let it go through the acceleration chamber, and using magnetic and/or electrostatic devices to change its velocity, and it exits. its kind of like a coil gun, but instead of accelerating a projectile, you accelerate the natural occurring dust and gas particles in space. never does the ship in question expand any propellant. it is by no means a reaction-less drive. by imparting acceleration to particles of the ism, you get the equal and opposite momentum that you impart on it. its not much momentum, but its some. my hope is that having a nuclear reactor (not a nuclear engine, the purpose of the reactor is to provide electrical power for the drive hardware) onboard, you could run the drives continuously for a long periods of time (decades). there is no confusion here, ive read about all kinds of drive systems, i dont think ive read anything like that.

[Herra Tohtori]

@Herra: that is a bit of a nitpicking, if you checked more of the articles then it will be abundant that the writers are *very* much aware that specific impulse (the speed at which propellant leaves the engine, divided by its mass) can have massive effects.

That's why most realistic designs use electric (ion, field-effect, etc.) engines since they have a massive isp.

You also made a not entirely correct assertion, as merely lowering the craft's mass (without changing any engine parameters) would include carrying less fuel, which we all know won't result in more delta-v. However if we amend, that lowering the mass of ship components beside fuel, then yes - it would produce more delta-v. However that's the very same thing as increasing the ship's fuel-to-mass ratio.

Yep, I meant the dry mass of the ship. But propellant-to-ship mass ratio and total delta v doesn't translate directly to combat efficiency - increasing propellant/ship mass ratio by increasing the amount of propellant onboard will increase delta v but reduce acceleration (assuming the engine stays the same), while increasing propellant/mass ratio by reducing dry mass increases both acceleration and delta v.

What the entry refers to is sticking a "bigger" engine on a craft. It will give more thrust, but isp for a given technology is set or at least won't scale that much with size... as a result you won't gain any (significant) delta-v, only the ability to accelerate, ergo reach your delta-v faster.

So to sum it up:
Delta-v is the result of your technology specific isp and your fuel fraction.
Acceleration is the result of your technology specific isp and the size of your engine.

Yeah, I amended my post with an edit, because I frankly disagree with the assumption that specific thruster technology would always have more or less same ejection velocity.

With chemical rocketry, this assumption holds true because the gas expansion velocity is limited. However, with most other technologies, the ejection velocity can be scaled up by increasing reactor output power to engine.

Though I suppose the maximum factor limiting the ejection velocity of an ion drive engine would be vacuum's permittivity - that would largely define how strong an electric field you can use to accelerate the propellant without creating arcs of electricity through the engine itself. Using a nuclear reactor to heat up gas, accelerating it by expansion would be limited by the maximum reactor temperature which of course is limited by materials' thermal durability.

So maybe there are natural maximum performance limits for each specific propulsion technology. But the assumption that all the engine systems would be developed to the maximum is quite interesting.

I do agree with what the emphasis of the text was - that increasing propellant flow doesn't increase delta v, only acceleration (and propellant lasts shorter duration of time, obviously) and that if ejection velocity stays constant, the only way to increase delta v is to increase the ship's propellant/mass ratio.

I just felt that it was necessary to specify that the "thrust" of the engine can be increased by either increasing mass flow or ejection velocity. To be absolutely accurate, you can't even measure meaningful "power" for a thruster, so the term "more powerful" is a bit badly worded in either case...

[Flaser]

Another excellent thread was made by Memphet'ran on spacebattles.com:

http://forums.spacebattles.com/showthread.php?t=131056

It largely focuses on single ships and is a bit orthodox in the divide between missiles and ships, but it has a lot of sound conclusions and good insights. One thing it lacks compared to the Rocketpunk articles is the socio-economic grounding of the scenarios that Rocketpunk has so ingrained into its readers as of late.

The later are just like Charles Stross' space colonization beat down - which can be read here - wrought large - yeah it *can* happen, but will anyone bother when it won't make money? Namely, what's oft forgotten is how much all this stuff could cost. Granted we might get there one day - but not any time soon. Still even in our "romance" literature such sensibilities will still play a large role, so politics and economics which they arise from will have some hard effects on space combat.