sci-fi creative writting tips?

[manticore7]

How would I explain why a warship has energy based Point defence and secondary weapons, but use a Mass Driver as a main weapon. having trouble justifing that in my head.

Universe notes: Humans have been in space close to a thousand years and, have "normal" relations with a number of alien civilizations.

[Count Casimir]

Mass drivers are too big and bulky for the agile movements necessary for point defense, but they've got the necessary punch to break capital ship armor/shields/whatever.

That work?

[javcs]

An example would be Mass Effect.

Though, I have to say, I'd expect mass drivers would be made largely ineffective relatively early on, because (a) ships can maneuver, and (b) you'd need kinetic durability to deal with impacting space debris and such at higher relative velocities.

Oh, there you go, ships can't maneuver quickly enough to make mass driver rounds ineffective at typical combat ranges, but missiles are capable of sufficient evasive maneuvers to make mass drivers scaled for point defense ineffective.

Or, you just have main battery mass driver armaments be capable of that much awesomeness, being vastly easier to scale upwards safely and reliably than the energy weapons.

[Mr Bojangles]

I suppose in order to answer your questions, we'd need to know more about the universe that you've created. Do your warships have energy shielding (magnetic/plasma-based deflectors)? Are sensors bound by the speed of light? What are the typical engagement ranges? Do your ships have reactionless drives or some form of inertial control? Are strikes against relatively stationary targets (e.g., large space stations) typical? Is orbital bombardment common? How much power can the reactors of your ships output?

With energy shielding in place, kinetic rounds would have an easier time punching through. If ships use reactionless drives, then depending on range, they would be able to change velocity more than rapidly enough that they could avoid kinetic rounds. Against slow-moving/stationary/planet-bound targets, mass drivers would be absolutely devastating. Energy output matters, too, so a slower firing mass driver might be more energy efficient than rapid fire lasers (or whatever your ships use).

[ed_montague]

You could just put technological limitations on this hypothetical human civilization. We're doing fine, and some kindly soul has passed us blueprints for [insert item here]; we've managed to reverse-engineer this item, and it allows us to install energy weapons on our warships, but we haven't quite yet figured out how to scale it up, so we stick to mass drivers for the big guns. Or some big galactic U.N. equivalent has put a ban on certain types of weaponry just because.

[fredgiblet]

In order for mass drivers to be useful they have to be too large for their turrets to move quickly enough for point defense. Alternately they are too large for turrets period (spinal mounts) and thus, obviously, can't do point defense.

[Michael]

Mass Drivers would be powered by electro magnets, I would imagine that it costs much less power to charge them and fire the shell, than to have an energy weapon in its place, especially if you're point defence is energy weapons (which you can get away with 'cos while there's more they're significantly less powerful as you'd only need to glance something as fragile as a missile to do massive damage to it).
Also, if you're ships are really long, the magnetic coils could run the length of the ship, I think you'd be able to accelerate the shell to a fraction the speed of light like that, making shields a little bit pointless then

[daelyte]

don't forget heat dissipation, which is an even bigger problem in space

excess heat can cause problems such as melting of equipment, decreased safety of personnel, and easier detection by enemy forces

energy weapons use energy, and that produces waste heat which must be disposed of... if they're small its not a big problem, but as primary weapons they would cause a lot of heat which would require more heat sinks

kinetic weapons would require less energy, produce less heat, and (partly because they're an older technology) operating them would cheaper and safer in personnel as well as the equipment itself, but increasing the speed of projectiles has an exponential energy cost

lasers (and similar) move at the speed of light, so they'd be worth the extra heat to shoot down missiles and other fast targets, that speed is the same regardless of size so most of the scaling issues are with the amount of damage done which makes them less suitable for punching through capital ship defenses

it would make sense for secondary weapons to be a mix of the two, depending on ship roles, etc

[fredgiblet]

When you're talking about energy requirements and muzzle velocity for mass drivers you need to remember that the energy requirements go up by the square of the velocity. That means that when you double the muzzle velocity you square the energy needs and that's not even looking at the rapid drop in efficiency that's going to occur as well. This becomes highly impractical very quickly and will realistically limit mass driver viability severely.

Energy weapons should generally scale much better.

[daelyte]

@fredgiblet:
Exactly, but you can scale up the projectile mass easily enough to cause more damage.

Thus for applications that don't require such high velocity, kinetic weapons may be preferable in terms of energy/heat efficiency.

http://www.projectrho.com/public_html/r ... Efficiency

http://www.projectrho.com/public_html/r ... -Coil_Guns

[fredgiblet]

Scaling up the projectile mass also scales up the power requirements. Additionally the mass driver itself may produce less waste heat than a laser or other energy weapons, but they're still going to need power, and that power has to come from somewhere. I note in your links that they give a rough estimate for efficiency for lasers, but none for mass drivers. My expectation is that the efficiency for mass drivers will be lower, for high-velocity ones MUCH lower.

In a hard sci-fi setting based off of physics we know mass drivers are only likely to be useful against stationary or otherwise non-maneuvering targets. This isn't, of course, to say that you can't soften mass drivers easily to make them competitive, it's just a diamond-hard sci-fi mass driver is going to be limited more than many other options

EDIT: It looks like they did give an estimate for efficiency for coilguns. 90% percent. That's...pretty ridiculous if you're talking about a high-end system. Although the rest of the calculations appear to be correct at a glance.

[Mr Bojangles]

@daelyte:

Here is some extensive info on coil guns:
http://wiki.4hv.org/index.php/Coil_gun

Suffice it to say, they aren't very efficient at all:
http://wiki.4hv.org/index.php/Coil_gun#Efficiency

Magnetic guns in general aren't terribly efficient. As fred points out, energy goes up by the square of the velocity of the projectile, and it scales linearly with projectile mass. The more energy you need, the more current you pump, the more heat you will produce. The more heat you produce, the less magnetic your magnet becomes (literally; see the Curie temperature), which would require more more current to overcome, which produces more heat; well, you see where this is going (melted electrical feeds and magnetic coils).

One way to overcome the issue of heat would be superconducting magnets, but then you need large refrigeration systems. Or, you could make your barrel long (very, very long), providing a slower acceleration and mitigating some of the heat. In both cases, your mass driver is big and bulky.

To me, it would seem that in any sci-fi story that focuses on reality, a mass driver would be a siege weapon. A slow-firing, spinal mount cannon meant to bombard planetary targets or large objects moving in known orbits around said planet.

[daelyte]

Here is some extensive info on coil guns:
http://wiki.4hv.org/index.php/Coil_gun

... from hobbyists.

http://en.wikipedia.org/wiki/Coilgun#Potential_uses

Small coilguns are recreationally made by hobbyists, typically up to several joules to tens of joules projectile energy (the latter comparable muzzle energy to a typical air gun and an order of magnitude less than a firearm) while ranging from under one percent to several percent efficiency.

Much higher efficiency and energy can be obtained with designs of greater expense and sophistication. Bondaletov in 1978 in the USSR achieved record acceleration with a single stage by sending a 2-gram ring to 5000 m/s in 1 cm of length, but the most efficient modern designs tend to involve many stages.[11] Above 90% efficiency is estimated for some vastly larger superconducting concepts for space launch.[8] An experimental 45-stage DARPA coilgun mortar design is 22% efficient, with 1.6 megajoules KE delivered to a round.

As fred points out, energy goes up by the square of the velocity of the projectile, and it scales linearly with projectile mass.

Doesn't the energy requirements for laser cannon firepower scale up linearly too? The same heat dissipation that is needed for a large coilgun should be able to handle small point defense lasers, but larger ones could be a problem.

Oh and I just found this on ProjectRho too:

Laser bolts grow weaker with distance but a nuclear warhead has the same strength no matter how far the missile travels.

So lasers would have a limited effective range. I wonder how coilguns compare? I'm guessing the low friction typical of non-atmospheric combat wouldn't slow down coilgun projectiles all that much, so they'd have longer range.

As well as this elsewhere on the same site:

There are also two other limits: the maximum aspect ratio of the hole is usually less than 50:1, and the actual drilling speed, for efficient drilling, is limited to about 1 meter per second (depending on the material).

However, under combat conditions there is no way one could focus the laser down that tiny and keep it on the same spot on the target ship for multiple seconds.

So it would seem that lasers are not so great against armor.

To me, it would seem that in any sci-fi story that focuses on reality, a mass driver would be a siege weapon. A slow-firing, spinal mount cannon meant to bombard planetary targets or large objects moving in known orbits around said planet.

They might also be viable against targets that aren't moving too quickly, such as heavily armored capital ships. So long as they don't move faster than your projectile, you just need to aim towards where they're going to be instead of where they are now.

Against missiles and fighters, you'd be better off with missiles or lasers IMO.

[fredgiblet]

Doesn't the energy requirements for laser cannon firepower scale up linearly too?

Yes.

The same heat dissipation that is needed for a large coilgun should be able to handle small point defense lasers, but larger ones could be a problem.

The energy requirements for the coilgun may very well be higher than for the laser, possibly by a significant amount. In order to be an effective weapon we're talking hundreds of kilometers per second minimum.

So lasers would have a limited effective range. I wonder how coilguns compare? I'm guessing the low friction typical of non-atmospheric combat wouldn't slow down coilgun projectiles all that much, so they'd have longer range.

Absolute range is effectively unlimited for mass drivers. You could bombard a planet in another solar system if you had a hundred years to wait. The effective range will be much shorter. Firing a mass driver is not going to be a quiet event, so you need to get the projectile to the target ship before they can dodge out of the way, depending on the acceleration and size of ships involved you might only have a few seconds.

So it would seem that lasers are not so great against armor.

True, but particle beams are.

They might also be viable against targets that aren't moving too quickly, such as heavily armored capital ships. So long as they don't move faster than your projectile, you just need to aim towards where they're going to be instead of where they are now.

Moving faster than the projectile isn't necessary. If you shoot at where I'm going to be all I have to do is accelerate in a different direction far enough to make your shot miss me. If my ship is 20m wide all I have to do is displace by 20m in either direction and I'm good. You could attach guidance systems to your slugs, but then you have to make the guidance and propulsion systems capable of surviving hundreds of thousands of gs and you've added weight that probably can't be acted on by the gun itself, reducing muzzle velocity.

[Absalom]

For mass drivers to be a reasonable main-armament, you need to be able to commonly hit the other guy with them. Here's a couple ideas:

1) Your FTL drives are attracted to each other, so you tend to wind up in close combat very quickly and easily.
2) Capital ships require massive endurance, which costs them enough maneuverability for mass drivers to have long-enough effective ranges.
3) You have a 'generic shield' technology (I'd probably say that it involves manipulating probability fields, or something equivalent), but because the dissipated energy has to go somewhere, mass driver rounds tend to result in feedback that destroys shield generators, while energy weapons might not even damage them.

Personally, at the very least I think I'd use 2, and maybe 3. For FTL I tend to prefer 'short-cut' systems like wormholes and routes through 'jump space' that involve less actual distance than a 'normal space' path between the origin and destination, so I'd skip 1.

[Mr Bojangles]

*snip*

All salient points, and yes, that was a hobbyist site. Doesn't change any of the math, though.

Fred actually took the words right out of my mouth, but I suppose I can think of a few more points for us to discuss...

The experiment by Bondaletov. While I couldn't find any direct documentation (yet), I don't doubt the veracity of the claim. However, it is unlikely that his coil set up actually survived the firing. It hits home the points of size and energy. Modern coil guns are generally staged affairs of some length in order to ensure both the launcher and the payload survive. From the Wikipedia article:

After NASA Ames estimated how to meet aerothermal requirements for heat shields with terrestrial surface launch, Sandia National Laboratories investigated electromagnetic launchers to orbit, in addition to researching other EML applications, both railguns and coilguns. In 1990, a kilometer-long coilgun was proposed for launch of small satellites.

(Emphasis mine).

In space, aerothermal considerations would be moot, but there would still be the issue of the heat generated during firing. A longer driver would help mitigate that issue, in addition to whatever cooling system was in place. Also, in your quote, it mentions a DARPA initiative to develop coil gun direct-fire weapons, i.e., mortars. As it stands with current physics and engineering, mass drivers as weapons would be relatively short ranged, fairly large and best suited to non-moving, or slow moving, targets. The future will likely hold some breakthroughs, though.

To your point about heat dissipation: your weapon systems would definitely share multiple heat sinking systems, but in all cases, your ship is going to glow in IR. Maybe even visibly, if you don't properly manage it. As you say, no matter the weapon system, heat will be a major problem in space. A novel means I came across was the droplet system in Mass Effect. Heat was dumped into liquid sodium or lithium heat sinks, which was then sprayed as a fine mist out of the front of the ship to be collected again at the rear. This had the effect of exponentially increasing the radiative surface area for cooling, without the drawback of having to use massive radiator panels.

[Fotiadis_110]

To your point about heat dissipation: your weapon systems would definitely share multiple heat sinking systems, but in all cases, your ship is going to glow in IR. Maybe even visibly, if you don't properly manage it. As you say, no matter the weapon system, heat will be a major problem in space. A novel means I came across was the droplet system in Mass Effect. Heat was dumped into liquid sodium or lithium heat sinks, which was then sprayed as a fine mist out of the front of the ship to be collected again at the rear. This had the effect of exponentially increasing the radiative surface area for cooling, without the drawback of having to use massive radiator panels.

Thing is, the energy requirements and waste issues of energy based weapons are likely even worse than mass drivers for the same kind of firepower.
In fact you can probably spit out a dozen shots of mass driver for the energy requirements of a single shot of plasma.
As for the droplet cooling system: it sounds awsome, but the issue then comes down to 'how hard is it to replace lost mass?'
While you capture remaining droplets, evaporative losses occur when exposed to low pressure envrionments.
Massive surface area simply makes the issue larger, not to mention hot things have a higher vapour pressure leading to increased losses.

[Michael]

I advise you manticore, to look at the description used by Mass Effect for their mass drivers, they do explain how they make work in game but I forget the description and it may help you in developing you're own one.

A question though: Could you not vent the heat sinks straight into space? If two ships or fleet are engaging each other then any attempt at stealth would be pointless as all the firing weapons would give away you position

[fredgiblet]

I advise you manticore, to look at the description used by Mass Effect for their mass drivers, they do explain how they make work in game but I forget the description and it may help you in developing you're own one.

They use, drumroll please, the Mass Effect to make them work. Run electricity through Eezo and you get a gravitational field, do it right and you get a gravitational mass driver.

Gravity control is probably one of the better softening methods to make mass drivers competitive.

question though: Could you not vent the heat sinks straight into space? If two ships or fleet are engaging each other then any attempt at stealth would be pointless as all the firing weapons would give away you position

How? Space is empty and you need somewhere for the heat to go.

Thing is, the energy requirements and waste issues of energy based weapons are likely even worse than mass drivers for the same kind of firepower.
In fact you can probably spit out a dozen shots of mass driver for the energy requirements of a single shot of plasma.

I wouldn't be quite so sure about that. While the BASE energy requirements of Directed Energy Weapons may be higher my expectation is that the efficiency will be higher as well, meaning that the effective energy requirements of mass drivers will be higher. Of course this is speculation, but when you consider that you are trying to directly overpower physics with a macroscopic, fractional c mass driver I very much doubt that efficiency will be possible.

On the other hand even if it's true a dozen mass driver rounds flying harmlessly past me while my one plasma shot actually hits means I'm still ahead of the game.

[Arioch]

You could allow the heat to boil some coolant and then vent the gas into space. Not sure how efficient that would be.