Exploring Efficient Weapons in Sci-Fi Settings

[essenmein]

Been doing a bit of reading re weaponry, and the general conclusion is that mass throwers of some sort beat energy weapons (odd term, basically both are "energy weapons", kinetic or other wise).

One thing I'm stuck on is the "if you have anti gravity why bother with literally anything else as, just use the AG to accelerate rocks at the baddies".

On the surface this makes sense, but a slightly deeper look to me makes it not so clear, since efficiency should be a huge influence, ie how much damage you get from how much of your own input (since you have to carry this "input" with you).

In my world I try to follow the "few big lies" principle, make some rules around this but otherwise its hardish sci fi. So the few big lies are the sci fi standards, FTL, anti grav and anti matter, all three are intrinsically linked as the base phenomena involves gaining control over negative energy/mass (don't try to explain, that's the fiction part!).

(note below when talking "units" I'm referring to mass-energy equivalence)

So if I look at this from an efficiency perspective, let's say my anti grav is 100% efficient (it won't be, but just as an example), then 1unit of (say) electrical energy makes 1unit of kinetic energy in the projectile, so far so good, my bullet gets 1unit of kinetic energy.

Now my anti matter process is also pretty good, 1unit of energy makes 1units of anti matter, but this 1units of anti matter now meets another 1units of normal matter (that I did not have to provide) to make 2units of energy. So to me at minimum anti matter weapons should have a factor 2x more destructive force per unit of input due to the fact that they use mass from their targets. In war getting 2x destruction for the same effort would be huge incentive to never bother with anti grav based launchers.

So IMO anti grav based mass throwers are very destructive, but not near as destructive as the same amount of energy used to make AM weapons.

Thoughts?

 

[Rive]

So IMO anti grav based mass throwers are very destructive, but not near as destructive as the same amount of energy used to make AM weapons.

Actually, what I think is that the deciding factor would be the possibility of stocking up instead. Just like the actual railgun controversy: to have enough peak power to launch a projectile on electrical basis you need some really heavy machinery - on the other hand, to do it by chemistry you need some explosives only.
There are limitations of course, but it is really difficult to beat the ammo rack.

AM weapons would be also about throwing mass, right? But you need less energy during launch since the small projectile for the same destructive power. So you can stockpile with only a limited peak power in cruise mode - having your main reactor available for the engines in combat.

 

[essenmein]

Actually, what I think is that the deciding factor would be the possibility of stocking up instead. Just like the actual railgun controversy: to have enough peak power to launch a projectile on electrical basis you need some really heavy machinery - on the other hand, to do it by chemistry you need some explosives only.
There are limitations of course, but it is really difficult to beat the ammo rack.

AM weapons would be also about throwing mass, right? But you can stockpile with only a limited peak power in cruise mode - having your main reactor available for the engines in combat.

The peak power requirement argument is absolutely valid. Here IMO AM wins hands down. Reactor take 10 min to make enough AM for one weapon, that weapon releases that energy in micro seconds.

If you are at the "can just make AM" level of tech, you reach kind of an asymptote, e=mc^2, no matter what form it takes, mass or energy, it weighs the same and you have to carry it with you...

 

[essenmein]

Also FWIW near c velocities are not achievable, they can jump (einstein rosen bridge), but limited to about 0.1-0.2c for sublight (due to dilation effects), and arbitrary engine tech limited max velocity of about 0.35c.

Saw some math somewhere that showed a mass traveling faster than about 0.89c the kinetic energy of that object exceeds the energy in the mass (e=mc^2). So I'm going to avoid the issue of masses traveling at velocities where the resultant kinetic energy exceeds the energy in the rest mass.

 

[Klystron]

Proliferation of anti-gravity devices in science fiction probably owes more to artistic license than weapon design. Depicting and filming free-fall is difficult, expensive and may even detract from the plot. Much easier to stipulate ship-wide artificial gravity and get on with telling the story than to have actors floating around the sound stage when not accelerating. Convenience over realism.

In other words artificial gravity suffices to explain Earth normal gravity in spaceship scenes but is usually not sufficiently developed to use as a plot device; that is, as a directed weapon.

 

[gleem]

One thing I'm stuck on is the "if you have anti gravity why bother with literally anything else as, just use the AG to accelerate rocks at the baddies".

Let the force be with you.

 

[DaveC426913]

Depicting and filming free-fall is difficult, expensive and may even detract from the plot. Much easier to stipulate ship-wide artificial gravity and get on with telling the story than to have actors floating around the sound stage when not accelerating. Convenience over realism.

Yeah, they didn't even attempt low-g on the Moon in the latest "realism" sci-fi Ad Astra.

 

[essenmein]

Proliferation of anti-gravity devices in science fiction probably owes more to artistic license than weapon design. Depicting and filming free-fall is difficult, expensive and may even detract from the plot. Much easier to stipulate ship-wide artificial gravity and get on with telling the story than to have actors floating around the sound stage when not accelerating. Convenience over realism.

In other words artificial gravity suffices to explain Earth normal gravity in spaceship scenes but is usually not sufficiently developed to use as a plot device; that is, as a directed weapon.

No doubt true, however I'd like to have it well enough thought out so the implications of technologies are at least a little more developed and more importantly considered in war strategies and what the vessels look like.

So anti gravity in my story is tasked with some pretty heavy duty requirements. Keeping 1G in the correct direction for the occupants inside is actually the easy part, preventing those occupants becoming red smudges on walls, or keeping the ship from tearing itself apart due to accelerations from maneuvering are its primary task. So locally it must be capable of canceling the effects of maybe 1000's of G's.

Which raises the question, if you can do this, does it make sense as a weapon? Specifically claims on the internet (eg TVtropes) that if you can do this, no other weapons even make sense! The efficiency aspect jumps to mind as a good reason why its NOT used, it is feasible, but just not as effective in terms of ship energy system use as other weaponry. I'd like this to seem plausible, not just handwavey because I said so.

 

[essenmein]

Since thinking implications of various technology, with anti gravity fields you have basically "shields" against mass projectiles, ie if you can cancel 1000's of G inside your ship, surely you can also decelerate incoming projectiles...

 

[DaveC426913]

Which raises the question, if you can do this, does it make sense as a weapon? Specifically claims on the internet (eg TVtropes) that if you can do this, no other weapons even make sense!

It still remains a matter of debate how small, stable, reliable, economical, portable, controllable and above all - tactically effective - such a weapon might be.

Think about the 1940s saying "We can split the atom and make H-bombs. That's so efficient, no other weapons make sense!"

That's not true, by a long shot.

 

[Rive]

No doubt true, however I'd like to have it well enough thought out so the implications of technologies are at least a little more developed and more importantly considered in war strategies and what the vessels look like.

Above a level of speculation the issue is no longer technological in nature, but about the reasonable limitations to keep the story in check and prevent weapons becoming an 'I won' buttons or 'I won, but there are no survivors in the galaxy' type WMDs => matter of good technobabble.

 

[essenmein]

Above a level of speculation the issue is no longer technological in nature, but about the reasonable limitations to keep the story in check and prevent weapons becoming an 'I won' buttons or 'I won, but there are no survivors in the galaxy' type WMDs => matter of good technobabble.

True, I just want to avoid gaping plot holes, like having technology that is effectively a super weapon but it's only use is to hold people on the ground because of lazy story writing. I can't not address this if internet sites on Earth already worked out artificial gravity is a super weapon!

 

[essenmein]

It still remains a matter of debate how small, stable, reliable, economical, portable, controllable and above all - tactically effective - such a weapon might be.

Think about the 1940s saying "We can split the atom and make H-bombs. That's so efficient, no other weapons make sense!"

That's not true, by a long shot.

Working through all the tactical stuff is kind of where I am at the moment. The first step there though is working out logically what my available weapons actually are based on the tech that I've made available.

 

[DaveC426913]

... like having technology that is effectively a super weapon but it's only use is to hold people on the ground because of lazy story writing.

Indeed, you have (independently?) stumbled upon one of the Laws of Sci-Fi:"The effectiveness of a propulsion system as a weapon is directly proportional to its effectiveness as a propulsion system."
- paraphrased - and I can't remember the author

They made this mistake this in the script of SW: The Last Jedi.
1] Ships that go to hyperspace can ram enemy ships with devastating effect.
2] Hyperspace drives are small enough to fit in an X-wing.

Oops. The Rebels just invented unmanned hysperspace Star-Destroyer-killing torpedoes.
As long as they can produce hyperspace drives they don't have to sacrifice another person.

 

[essenmein]

Indeed that one move basically broke the whole universe, why bother with three movies worth of story telling when a few old freighters with hyperdrive would have dealt with the death star.

Although I did read some fan fiction explanation about why this worked on snokes ship, namely that the new order or what ever they are called were an isolated faction and they are the only one that had the hyperspace tracking thing, and that worked by "having a presence in hyperspace", so they rammed its hyper space shadow or something. Since that ship was the only one with the tracker, it only worked on that ship.

Although during lead up to that action in the movie, no where did they elude to this being a special trick that only works on this one ship, it seemed like they were just good old hyperspace ramming like they have always never done (why was autopilot not sufficient?!).

Its a little ridiculous that basically fans had to make up a plausible sounding explanation because the writers broke their own story so badly.

 

[Rive]

"The effectiveness of a propulsion system as a weapon is directly proportional to its effectiveness as a propulsion system."
- paraphrased - and I can't remember the author

From Larry Niven: Kzinti Lesson

 

[Rive]

The first step there though is working out logically what my available weapons actually are based on the tech that I've made available.

With those speed/acceleration parameters I think the most important part is that any battle would end long before the (biological) crew would be able to notice that it has started.
Also, effectiveness of radars and such would be reduced, since due the return trip of the signal and the inevitable delay in the circuitry there is just limited time to react. Also, the long ranges makes the signals weak and noisy.
I think in such environment permanently deployed complex/fragmented gravity fields (to sweep aside any pebbles or bullets) would be the most basic form of defense.

 

[stefan r]

If you have gravity manipulation you can disect neutron stars using controlled antigravity. You could keep a high gravity field around a relatively small dwarf planet mass of Neuton material. Makes a significant neutron bomb.

 

[DaveC426913]

From Larry Niven: Kzinti Lesson

I know he's used it, but I'm pretty certain he didn't create it.
It was one of his contemporaries - Pournelle or Scalzi or Pohl or Brin or one of those guys.
Wish I could find the reference. There's a bunch of corollaries - other related laws - associated with it.

 

[DaveC426913]

If you have gravity manipulation you can disect neutron stars using controlled antigravity. You could keep a high gravity field around a relatively small dwarf planet mass of Neuton material. Makes a significant neutron bomb.

If you have gravity manipulation of sufficient power to dissect a neutron star, you don't need a neutron star. Just dissect the enemy ship instead.

 

[Rive]

I know he's used it, but I'm pretty certain he didn't create it.

Did not know that. It's not really surprising, though: that generation of writers shared a lot.

 

[essenmein]

If you have gravity manipulation you can disect neutron stars using controlled antigravity. You could keep a high gravity field around a relatively small dwarf planet mass of Neuton material. Makes a significant neutron bomb.

We have magnetic manipulation today, yet oddly we don't have magnetar magnets.

Just because we know how something works does not mean we can go straight to creating 10^10 Tesla fields found in a magnetar, we haven't even crossed 100T!

So even if somehow you could develop gravity field generators, that doesn't mean immediately you get to make 10^11G found on a neutron star.

Then, if you could, you don't need to go to a neutron star to get a spoon of neutrons, you can make your own, I mean at that level of gravity manipulation, just collapse the target planet/ship to neutron star density, and then remove the field. I imagine the resulting explosion would probably wipe out that systems star.

 

[essenmein]

With those speed/acceleration parameters I think the most important part is that any battle would end long before the (biological) crew would be able to notice that it has started.
Also, effectiveness of radars and such would be reduced, since due the return trip of the signal and the inevitable delay in the circuitry there is just limited time to react. Also, the long ranges makes the signals weak and noisy.
I think in such environment permanently deployed complex/fragmented gravity fields (to sweep aside any pebbles or bullets) would be the most basic form of defense.

So far battles are essentially chases. The extremely hostile alien (for various reasons) are faster than us (at sublight, no engagement is possible in FTL), so they tend to match trajectory and catch up, then slow so relative ship to ship velocity is sufficient for their weaponry to be effective (mass throwers).

(Wreckage of already destroyed ships still traveling at the faster velocity catching us first has some pretty negative impacts!)

If distances are too great or relative velocities too high, neither side can hit the other, and since the aliens are both faster and aggressively hostile, they make sure that they can shoot at us, which means by extension we can shoot at them.

(You might notice that this is a loosing position for the protagonists to be in)

 

[essenmein]

"The effectiveness of a propulsion system as a weapon is directly proportional to its effectiveness as a propulsion system."

Figured I'd run some calculations around the ships I'm proposing.

The larger ship we find is ~2800m long, and ~800m diameter. If I assume a 50% fill factor with something like steel I get a ship mass of around 5e12kg.

At 0.1C this thing has about 5 orders of magnitude more impact energy than the Chicxulub impactor... lol

0.001C is the same impact force as Chicxulub...

The ships reactors would have to burn about 2.5e10kg in mass to do this (0.1C), or about 0.5% of the ships total weight, sounds like a lot but 0.5% of the ships weight consumed feels within the realm of how much fuel you can bring. (for example an F18 hornet take off weight for attack missions is over 50% fuel)

I was originally thinking 0.2C might be a reasonable max speed, but I think I'm going to have to seriously re think that one!

Maybe even 0.1C is still wayyyyy too fast.

Man space reality sucks.

 

[Zachsphy]

Been doing a bit of reading re weaponry, and the general conclusion is that mass throwers of some sort beat energy weapons (odd term, basically both are "energy weapons", kinetic or other wise).

One thing I'm stuck on is the "if you have anti gravity why bother with literally anything else as, just use the AG to accelerate rocks at the baddies".

On the surface this makes sense, but a slightly deeper look to me makes it not so clear, since efficiency should be a huge influence, ie how much damage you get from how much of your own input (since you have to carry this "input" with you).

In my world I try to follow the "few big lies" principle, make some rules around this but otherwise its hardish sci fi. So the few big lies are the sci fi standards, FTL, anti grav and anti matter, all three are intrinsically linked as the base phenomena involves gaining control over negative energy/mass (don't try to explain, that's the fiction part!).

(note below when talking "units" I'm referring to mass-energy equivalence)

So if I look at this from an efficiency perspective, let's say my anti grav is 100% efficient (it won't be, but just as an example), then 1unit of (say) electrical energy makes 1unit of kinetic energy in the projectile, so far so good, my bullet gets 1unit of kinetic energy.

Now my anti matter process is also pretty good, 1unit of energy makes 1units of anti matter, but this 1units of anti matter now meets another 1units of normal matter (that I did not have to provide) to make 2units of energy. So to me at minimum anti matter weapons should have a factor 2x more destructive force per unit of input due to the fact that they use mass from their targets. In war getting 2x destruction for the same effort would be huge incentive to never bother with anti grav based launchers.

So IMO anti grav based mass throwers are very destructive, but not near as destructive as the same amount of energy used to make AM weapons.

Thoughts?

While you can probably achieve severe damage with a rock shooting out really fast, it’s nowhere near as cool as a laser. I’m pretty sure it’s just used to keep viewers entertained.

 

[DaveC426913]

The ships reactors would have to burn about 2.5e10kg in mass to do this (0.1C), or about 0.5% of the ships total weight, sounds like a lot but 0.5% of the ships weight consumed feels within the realm of how much fuel you can bring. (for example an F18 hornet take off weight for attack missions is over 50% fuel)

Wait. How did you arrive at these numbers? Don't you have to know the conversion rate of fuel to thrust?

 

[DaveC426913]

While you can probably achieve severe damage with a rock shooting out really fast, it’s nowhere near as cool as a laser. I’m pretty sure it’s just used to keep viewers entertained.

You're missing the point with KE weapons.

You don't have to shoot them out really fast.
You take advantage of the delta v between the two craft.
You simply drop a payload of diffuse mass in the path of the enemy - no targeting, little aiming - who cannot avoid it at these speeds, and they are pelted with shot moving at hyper velocity.

It's a technique suited to more physically realistic space battles - ships don't fight like airplanes - they build up high velocities and can't turn on a dime like in fantasy battles.

 

[Klystron]

You're missing the point with KE weapons.

You don't have to shoot them out really fast.
You take advantage of the delta v between the two craft.
You simply drop a payload of diffuse mass in the path of the enemy - no targeting, little aiming - who cannot avoid it at these speeds, and they are pelted with shot moving at hyper velocity.

It's a technique suited to more physically realistic space battles - ships don't fight like airplanes - they build up high velocities and can't turn on a dime like in fantasy battles.

Excellent points. Triple-A as far back as 1940's attempts to lay a barrage in front of moving aircraft using shells fused to explode either at the flight's relative altitude else in proximity to metal. The planes essentially fly into the flak sustaining damage. Sometimes called 'shotgun effect' or, if the gunners fire blindly at engine sounds, 'golden BB's'.

Early experiments replacing AAA guns with lasers could directly illuminate an aircraft or missile target but without causing much, if any, damage to the moving vehicle. Later models "splash" the target providing guidance for small missiles sensitive to the laser or maser wavelengths. In other words electronic weapons are commonly used to designate or 'light up' moving targets in order to direct kinetic or explosive weapons that do the damage or at least force a rapid course change.

SF authors looking for tense high-tech space war action might focus on the back-and-forth of energy weapons (EW), counter-measures (ECM), and counter-counter-measures (ECCM) as the military does.

 

[essenmein]

Wait. How did you arrive at these numbers? Don't you have to know the conversion rate of fuel to thrust?

The (fictional) ships are anti matter powered with a reaction-less "sublight" drive, mind you I did not consider "drive efficiency" here. The math was simply Ke=1/2mv^2 (Where m = mass of ship, an estimate in of itself), then m=Ke/c^2 (where m = mass equivalent of the resulting kinetic energy), note I did not calculate relativistic kinetic energy.

Mind you for any of this to have a hope in hell of working, due to the absurd power numbers involved in doing the acceleration in a reasonable amount of time, any significant inefficiency will result in an impractical level of heat dissipation.

 

[essenmein]

You're missing the point with KE weapons.

You don't have to shoot them out really fast.
You take advantage of the delta v between the two craft.
You simply drop a payload of diffuse mass in the path of the enemy - no targeting, little aiming - who cannot avoid it at these speeds, and they are pelted with shot moving at hyper velocity.

It's a technique suited to more physically realistic space battles - ships don't fight like airplanes - they build up high velocities and can't turn on a dime like in fantasy battles.

As a possible defense:
A single fairly large nuke detonated on the approaching mass cloud front with the detonation centered on the ships path would partially vaporize, and significantly alter the course of the remaining projectiles, creating a hole for the ships to fly through. Basically use the nuke to clear a path.

Alternately if using some sort of rocket (ie not reaction-less drive) simply spin the ships 180deg (ie full reverse thrust), and clear a hole through with the plasma plume.

 

[DaveC426913]

As a possible defense:
A single fairly large nuke detonated on the approaching mass cloud front with the detonation centered on the ships path would partially vaporize, and significantly alter the course of the remaining projectiles, creating a hole for the ships to fly through. Basically use the nuke to clear a path.

Alternately if using some sort of rocket (ie not reaction-less drive) simply spin the ships 180deg (ie full reverse thrust), and clear a hole through with the plasma plume.

The kinds of stories that employ KE weapons tend to be hard sci-fi, and use as real physics as possible, and verify the plausibility by doing the math. This is how Niven and his kin do their stories (Niven has a BA in Math from CalTech). Those defenses you suggest would never fly in his stories, because the math won't back them up.

 

[essenmein]

The kinds of stories that employ KE weapons tend to be hard sci-fi, and use as real physics as possible, and verify the plausibility by doing the math. This is how Niven and his kin do their stories (Niven has a BA in Math from CalTech). Those defenses you suggest would never fly in his stories, because the math won't back them up.

I'd be curious what aspect of nuclear flak wouldn't work. I would have assumed that the addition of a pile of energy would at least divert the masses from their trajectory.

I don't know much about the Man-Kzin wars or the known space universe, but have been reading up on them just now.

(from reading wiki)

In the first man kzin war, a bussard ramjet craft was used to accelerate iron slugs to 0.99c to devastate wonderland. And then later the outsiders gave the humans hyperdrive.

This already doesn't seem feasible or have math backing. Esp from an energy perspective:

 

[GTOM]

I'd be curious what aspect of nuclear flak wouldn't work. I would have assumed that the addition of a pile of energy would at least divert the masses from their trajectory.

I don't know much about the Man-Kzin wars or the known space universe, but have been reading up on them just now.

(from reading wiki)

In the first man kzin war, a bussard ramjet craft was used to accelerate iron slugs to 0.99c to devastate wonderland. And then later the outsiders gave the humans hyperdrive.

This already doesn't seem feasible or have math backing. Esp from an energy perspective:
View attachment 255376

The problem is that both nukes and rockets expend lots of energy, but pretty much unfocused, like a flamethrower against a bullet.

 

[GTOM]

Otherwise, while anti matter weapons make big explosion, but it is very dangerous to store it. Also the faster the weapon the harder to defend against it.

 

[essenmein]

The problem is that both nukes and rockets expend lots of energy, but pretty much unfocused, like a flamethrower against a bullet.

Kinetic energy is vector quantity, so I agree its not going to stop it, that is not the goal, the idea is to give it a gentle nudge normal to the direction of travel where even a fractional change in trajectory over large distances in space would make it completely miss the intended target.

More plausible is that a relativistic object may not spend enough time in the fireball of a nuke to impart any significant Ke on it even if it is normal to its travel.