Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Cryxis, Prince of Doom]

Well it's not meant to be ideal, it's meant to be cheap.

What's easier/cheaper, transporting many special designed rounds or grabbing a couple asteroids and fitting them into the barrel?

[Rolepgeek]

Long run?

The rounds. Rather than needing to fix your barrel when that one asteroid obliterates the front fifth of your ship/barrel after splintering under the forces you're making it undergo.

[Parsely]

Some of the smallest asteroids are 1km in diameter, that means you need a bore diameter in excess of 1km. That's absolutely insane. Not to mention the massive amount of energy it'll take to get that thing moving.

[GiglameshDespair]

Frankly the cost of producing a few rounds for a railgun is insignificant compared to the cost of producing a spaceship built for war.

You've also got to consider more than just the cost of ammunition for your railgun, you've got to consider logistics. If you're not taking asteroids with you, you're going around with no ammunition for your weapon. If you are taking asteroids around with you, why not just take produced rounds as something that will take less space and work better?

To make asteroids into weapons, you've also got to spend fuel travelling to them, capturing them, and then you have to have both the machinery and resources to convert them into usable munitions. That costs, too. In the mean time the enemy has already shot you with their railgun. Or travelled to your base of operations and shot it with their railgun.

As asteroids, they'll have different compositions and weights, so each will shoot differently. If they've got an unstable structure, the stress of firing could perhaps cause them to break. That's really not something you want to happen, either in the railgun or once fired.

Some of the smallest asteroids are 1km in diameter, that means you need a bore diameter in excess of 1km. That's absolutely insane. Not to mention the massive amount of energy it'll take to get that thing moving.

I'm assuming he just mean generic space rocks of any size.

[Cryxis, Prince of Doom]

Yeah generic space rocks


And this would be a more specialized ship meant for well going into a fight where you know you have asteroids laying around.

You wouldn't haul asteroids with you, you would just bring this ship along in engagements where you know there are plenty of resources but yes I think you are all correct with manufactured rounds being just better in all circumstances





You said it would be bad of it broke up after leaving the barrel? Wouldn't that cause a sort of shotgun effect? Which I guess would be bad if prediction is what you were aiming for but wouldn't that be good for say shooting up a base or large group of fast moving ships?

[Amperzand]

The issue with that is distance. Going from a conventional shotgun firing combat buckshot, the pellets spread steadily from the muzzle, equating to about a foot-wide circle about 50 feet from the muzzle. Another 50 feet, and they're spread around a considerable area, leaving insufficient firepower on any one target to actually be worth much, AFAIK. Now imagine instead of fifty feet, the spread has to remain useful over 50 miles, or 50,000 miles, entirely valid ranges for space combat. I've seen it said that if two embattled vessels are actually within naked-eye visual range of each other, somebody fucked up hugely.

[GiglameshDespair]

Space is big. Real, real big. The distances are huge, and ships are tiny by comparison. "Close together" is not close like you're thinking. You may be fighting at distances it takes light several seconds to reach your enemy. Space combat ain't easy. The light-speed lag also means you know where they were, but you have to calculate where they are and where they're going to be. You have to hit where they're going to be in the very small space of time that they're there.

Each piece of the blast will have a different velocity, so you can't aim precisely with it. If you're not aiming precisely at where they're going to be, you're going to miss. It's simply not valid as a weapon for space.

Against a static target, it might work in the wood-axe to battle-axe way, but... a base would likely have defences against rogue space rocks that might threaten it. Lasers, perhaps, smaller mass drivers, whatever. The smaller the pieces, the easier it is to counter as each has less individual energy, and the more effectively any base armour would protect against it.

[Amperzand]

Keep in mind that the thing in The Moon is a Harsh Mistress was firing at a range of merely 8 light seconds, at a target tens of thousands of miles across.

[Culise]

You said it would be bad of it broke up after leaving the barrel? Wouldn't that cause a sort of shotgun effect? Which I guess would be bad if prediction is what you were aiming for but wouldn't that be good for say shooting up a base or large group of fast moving ships?

Two reasons.  First, presumably your ship is not fighting alone, but is fighting alongside other ships.  This is a bit of a presumption (if your situation is bad enough that you can't afford what are essentially metal slugs, this might be a jury-rigged pile of junk that you can only put into the field in isolation), but it does mean that your engagement envelope just expanded to include any of your escorts that happened to be on either side of the firing line between you and your target.  The second is the bane of so many things, the inverse-square law.  Basically, as a conical influence moves outward as a linear distance, the area covered expands proportionately to the square of that distance.  In the case of a directional radiator such as a laser or our space shotgun, this actual fall-off varies (lasers, f'rex, are much more susceptible to beam divergence due to diffraction), but note that for any cone (that is, neglecting inter-particle collisions that may send your projectiles veering off wildly) with a fixed firing arc θ, the area of the circular area of effect (the base) is going to be proportional by that square to any linear variation in the distance h.

Spoiler: Specifically... (click to show/hide)

r / h  = tan θ
A = πr² = π(h tan θ)²
A = π h² tan² θ

So, let's put this into perspective.  Say you're one hundred thousand meters away from an object (that's a mere one thousandth of a light-second, very close range).  Instead of a solid object firing alone a line (θ = 0), you accidentally fire this thing off in a shotgun spread of...30°.  You've just spread your asteroid across over ten billion square meters of area by the time it reaches your target, even assuming it all reaches its destination in a conical pattern (it won't, by the bye; it'll be a sectored sphere, but I'm getting a bit of a headache at this point).  Assuming it's...say, the size of 25143 Itokawa (a respectable asteroid at about half a kilometer on its longest arc chosen mostly for a very convenient order of magnitude for its mass: 3.51*10¹⁰ kg) and that it somehow spreads perfectly evenly (it won't, but here we're into "perfectly spherical cow" territory), you are now delivering approximately 3.31 kg of space dust per square meter.  Not completely awful, but remember that (a) you won't be reducing the asteroid to sand as a part of your mishap, but rather randomly moving chunks that can be individually tracked and (b) you presumably needed the bang that came from that magnitude-ten difference, otherwise you wouldn't be firing something that size in the first place. 

By the bye, a kinetic space shotgun is arguably going to be the worst possible weapon to deal with highly-maneuverable ships, because they can track and dodge the projectiles much more effectively, and a miss is as good as a mile, whether it's by kilometers or millimeters.  It's the reason why bomb-pumped warheads, that so-recent staple of mil-SF that came about as part of some sort of Teller craze, are delivered so close to their targets by missiles before going off.  The inverse-square law is to SF physics what the square-cube law is to SF biology; it's a spoilsport.

Finally, though, imagine one final thing by analogy.  Imagine that you've created a sniper rifle, only every so often it fires a shotgun blast at random.  You can't control this, you can't select for it, and you've basically ended up in a situation where you're going to have your gun randomly firing in one or the other "mode" regardless of which role you place it in.  In other words, no matter whether you use it as a sniper or shotgun, you're going to have to deal with misfires.  It's not going to do particularly well in either role, in essence. 

NOTANEDIT: Also, Gig did this much faster than I.  And Amperzand points out the one reason you would use such a weapon - close range against something that can't dodge. 

[Parsely]

You know the asteroid belt? Standing on one 'roid, you need a telescope to see the next one in line, so to speak. When we're talking about space combat this is the kind of scale you need to be thinking in. If you're fighting in space you are doing it looking at a computer.

[Culise]

You know the asteroid belt? Standing on one 'roid, you need a telescope to see the next one in line, so to speak. If you're fighting in space you are doing it looking at a computer.

Yes and no, I would say; the low density of the asteroid belt has nothing to do with space combat.  "No" because it depends on your ability to apply a useful amount of damage (both in terms of raw damage delivered and the chance to hit) at a given distance.  The fictional Minovsky particles were (in)famous for this: by disrupting all uses of EM such as radar, they ended the rule of over-the-horizon combat and reduced combat (as intended by the writers) to visual ranges.  Your kinetic projectiles won't do much good if you fire them from so far out that the enemy can maneuver around them, your missiles won't do much if they can be shot down before getting close, and your lasers won't do much good if enemy ability to re-radiate the influx of energy outstrips the amount of power you can pump into a laser before beam divergence reduces its focus).  Purely as a hypothetical literary exercise, I believe circumstances can be conceived in which the best way to take out an enemy ship is actually to maneuver yourself into a physical boarding action; the fact that this results in anything from SPEHSE ROMANS to SPEHSE PIRATES IN THE SPEHSE AGE OF SAIL is not an unintended bonus.

"Yes" because if you're in space, computers are going to be what keep you alive.  Even in the aforementioned Gundam series where space melee is a thing, the suits were still piloted via computer screens hooked to cameras; when in combat, you don't open your front door (and put a giant hole in your armor) unless you're really desperate. 

EDIT:
Ah, and your edit did fix my question of relevance, I see.  Anyways, yes, I do agree in a general realistic sense that you cannot simply plop terrestrial scales (where for most of history visibility was artificially restricted by the horizon, at most in the low dozens of kilometers away); I'd just hesitate before adopting it as a hard-and-fast rule if we ever shift to writing. ^_^

[Amperzand]

Additionally, even visible range in space, assuming the civilizations in question know what a telescope is and the Minovsky particles don't disrupt visible light to any great degree, is going to be far beyond melee range. Sure, you can't use radar, but LADAR, telescopes, and the like leave you able to effectively aim dumb-fire projectiles, which I believe the Gundam universe was limited to, over distances that would be terrifying to anybody stuck with a SPAHSS SORD or complement of MURHEENS.

[Tuxfanturnip]

Keep in mind that the thing in The Moon is a Harsh Mistress was firing at a range of merely 8 light seconds, at a target tens of thousands of miles across.

The projectiles in TMIAHM were also guided, being originally designed as precision-landing space barges. What's really worth mentioning is that the target was non-accelerating (), being the closest thing to stationary in space combat.

Perhaps a mass driver could be used to turn asteroids into "rod from god" type precision kinetic bombardment weapons?

[Amperzand]

Oh, yeah, and planets don't accelerate, that too. My bad. :V

[Grimlocke]

On the subject of lobbing space rocks at things, wouldn't it be a lot easier to just grab one or more of them, fly really fast at the target and let go? One could use a gaggle of commandeered cargo vessels to overwhelm defenses by sheer volume and mass of the projectiles, assuming the target isn't something that moves around much like a drydock, space elevator, mining site, habitat, etc.