Energy Weapons VS Ballistic Weapons

[Agemegos]

I quite like the way that in the Known Space series Larry Niven has few actual 'weapons' and more high tech devices that turn out to be efficient as weapons (fusion drive, flashlight laser, digging tool etc). The only distinct weapon that I remember was 'the soft weapon' from the short story of the same name.

There were rifles and grenades in Protector IIRC.

 

[Agemegos]

A knife.
A sword.
A crossbow.
A pistol.

The pistol sounds okay. I'd rather have a shotgun, though.

I can't think of any reason to use the crossbow. Ammunition capacity, reload time, bad handling characteristics, and the inaccuracy of its drag-stabilised projectile in vaccuum make it seem worse in every way than a low-velocity submachine gun.

 

[Agemegos]

For one thing, right off the top of my head, you have atmospheric attenuation.

Yep. Consider the lensing effect of the air absorbing even a tiny proportion of your beam energy. Any beam with a power density high enough to burn through reflective heat-conducting armour (say, aluminium foil) is going to spread out to uselessness because of thermal bloom.

And that is even without the enemy filling the air overthe battle field with smoke and chaff. That is always going to be to hte advantage of one side or the other.

And then there is the fact that it is easy to armour against lasers: a reflective or smoke-generating ablative layer, a heat-conducting layer, and a refreactrory layer (say a ceramic sandwiched in aluminium-plaeted copper) should make a fairly thin and reasonable lightweight armour that is three orders of magnitude between at withstanding lasers than unprotected flesh.

 

[Agemegos]

This is what Ralts means by knockback; not the Hollywood misrepresentation, but the actual physical transfer of momentum from one (ballistic) object to another.

Transfer of momentum is always going to knock the bloke with the gun back at least as much as it does the bloke who gets shot.

I can believe that heavy weapons fired of tripods or carriages might knock their targets back, but in the case of anything sort of smallarms either the effect will be trivial or the weapon will be unusable.

 

[Agemegos]

But you're forgetting the potential versitality of hand weapons. Take phaser pistols on Star Trek. On the low settings, they can be used as highly effective non-lethal weapons, to create heat or cook food in emergancy situations, on the higher settings, they can easily disentegrate even an armored target, and be used as a cutting torch, and even overloaded and used as an impromptu hand grenade or explosive. That's a lot of utility out of a single device.

Yeah. It is also totally implausible. How are teh damned things supposed to work? Why shouldn't I suppose that magical technology might producce a hand-steamcannon that is even more versatile?

 

[Agemegos]

In Heinlein's The Moon Is a Harsh Mistress, rebels on the moon use mass drivers to bombard locations on Earth. The only implausible part is that:

a) The moon has been sending ore to Earth this way for years

Not ore. Wheat. In capsules with parachutes, fired on trajectories chosen to make them slow down in the atmosphere and soft-land.

 

[Falkus]

Yeah. It is also totally implausible. How are teh damned things supposed to work? Why shouldn't I suppose that magical technology might producce a hand-steamcannon that is even more versatile?

It's science fiction, you're not supposed to ask that sort of question.

 

[Agemegos]

Also, in a vacuum, a directed energy weapon can go an infinite distance, so long as it doesn't hit anything.

You are forgetting about diffraction. The tightest that any beam can be held in principle is a number of radians approximately equal to the wavelength divided by the beam width. In any sort of laser small-arm you are going to keep the beam narrow to give a high intensity at manageable power consumption, especially considering that you want to minimise attentuation by thermal blooming. The best way to do that is to use a very narrow beam, else the effect takes too long and vampirises too much of your pulse energy. I would be aiming for a sub-millimetre beam width, but lets consider a 100mm-wide flashlight-like beam to produce a generous limit.

Now various considerations suggest that laser smallarm aren't going to use a wavelength much shorter than about 100nm--you don't want to try a wavelength at which air is opaque, for a start. So very generously, beam width might be a million times wavelength. So at one kilometre the beam can be brought to a focus one millimetre across: it is effectively parallel. But at 1,000 km the beam is at least one metre across, and its intensity is only 1% of what it was at the muzzle. No laser smallarm is likely to be dangerous at a range of 1,000 km. That's a long way on a battlefield (620 miles), but nothing out in space.

Each further factor of ten in distance increases the beam width by a factor of ten and reduces beam intensity by a factor of one hundred.

 

[Agemegos]

It's science fiction, you're not supposed to ask that sort of question.

On the contrary. In science fiction you are supposed to ask that sort of question. It is in thinly disguised fantasy that you are not supposed to ask how things work and what they do.

 

[Falkus]

Nothing to see