Scifi Space Plasma Cannons... Totally Useless?

[kerbiloid]

1 hour ago, magnemoe said:

An sci-fi spaceship will have one plasma weapon, its drive. Any sort of fusion drive, orion or advanced fission like gas core will produce plasma as reaction mass. 

It produces charged particles which will make the beam dissipate right after the nozzle.
Also these can be deflected by magnetic field.

A neutralized particle (i.e. neutral hydrogen atoms) beam has better accuracy and much lower required power.
You don't need to turn the whole enemy ship into plasma, you just need to heat a thin spot on its surface to explode like a shell.

And you can't deflect the neutral beam with a magnetic shield.

1 hour ago, magnemoe said:

In most settings missiles will come from your front arch, to use the drive you need to turn around and trust.

Another advantage of a beam turret. You don't need to rotate.

Edited July 8, 2020 by kerbiloid

[K^2]

30 minutes ago, magnemoe said:

An sci-fi spaceship will have one plasma weapon, its drive.

Ah, yes, the Kzinti Lesson.

[magnemoe]

22 minutes ago, kerbiloid said:

It produces charged particles which will make the beam dissipate right after the nozzle.
Also thes can be defelcted by a magnetic field.

A neutralized particle (i.e. neutral hydrogen atoms) beam has better accuracy and much lower required power.
You don't need to turn the whole enemy ship into plasma, you just need to heat a thin spot on its surface to explode like a shell.

And you can't deflect the neutral beam with a magnetic shield.

Another advantage of a beam turret. You don't need to rotate.

 

1 minute ago, K^2 said:

Ah, yes, the Kzinti Lesson.

Imagine the engine as more as an close in weapon against missiles not for ship to ship combat, realistically 10k km is close range in deep space.
As said it will dissipate fast, but its still nothing you want to drive an thin skinned missile trough. 
The problem is the vulnerable engine, just have the first rounds of missiles carry lots of ball bearings who was released if missile was taken out. 

[KSK]

On 7/7/2020 at 5:54 AM, WestAir said:

Aye. KSK already shot down my entire comment, including my false statement on lasers, a few comments back:

Sorry if I came on a bit strong with that post.

Comments about writers are a bit of a personal sore spot, having seen a few too many opinionated posts on this forum (which were far less polite than yours) castigating writers and other artists for what they should or should not be.
 

That’s no excuse though - I need to back down a bit.

[magnemoe]

Want to derivative a bit here in the topic of engines, it seems to me that realistic spaceship engines is something who don't scale down well. In short an 30K ton ship will have an better or at least as good an engine than an 300 ton ship who again beat an 30 ton fighter who beat an 3 ton missile simply because good engines tend to be large. Now if engines has maximum effective size and its hard to spam because of cross heating large ships start loosing out: Destroyers are faster than battleships. On the other hand try to catch up with an nuclear powered carrier. 
Looks like this only start to get an issue then we get into destroyer scale ships in the first place, missiles and fighters seems to loose out here. Yes they can have an higher acceleration but would loose out on an stern chase because low ISP.  Now if the enemy comes to you this does not matter as much.

[kerbiloid]

1 hour ago, magnemoe said:

As said it will dissipate fast, but its still nothing you want to drive an thin skinned missile trough. 

What about two parallel rockets aside of the plume or a tungsten rod?

Also the rocket doesn't need to fly right into the ship. It can shoot sideways on fly-by.
https://en.wikipedia.org/wiki/Explosively_formed_penetrator

(It's a vacuum. The rocket may fly with the axis perpendicular to the velocity when its booster ends working and shoot from the closest point of trajectory directly into the ship.)

Edited July 8, 2020 by kerbiloid

[magnemoe]

3 hours ago, kerbiloid said:

What about two parallel rockets aside of the plume or a tungsten rod?

Also the rocket doesn't need to fly right into the ship. It can shoot sideways on fly-by.
https://en.wikipedia.org/wiki/Explosively_formed_penetrator

(It's a vacuum. The rocket may fly with the axis perpendicular to the velocity when its booster ends working and shoot from the closest point of trajectory directly into the ship.)

Or nuke pumped x-ray lasers for more effect, problem with Explosively formed penertators might be the engagement speed who can easy be faster than them
So you need to fire before you pass the ship, you probably want to spread out because of fire from the ship and screen probes anyway. 
Say the main benefit of using the engine this way is that you get a bit harder to hit and you can not get an direct hit with an nuke, downside is that you expose your engine. 

Edited July 8, 2020 by magnemoe

[kerbiloid]

4 minutes ago, magnemoe said:

Or nuke pumped x-ray lasers for more effect

Certainly

4 minutes ago, magnemoe said:

So you need to fire before you pass the ship, you probably want to spread out because of fire from the ship and screen probes anyway. 

Yes, it should fire before the passing, but why spread? Just compute the delay.

Also if the relative speed is much higher than the penetrator velocity, the speed of contact would increase a lot.

7 minutes ago, magnemoe said:

Say the main benefit of using the engine this way is that you get a bit harder to hit and you can not get an direct hit with an nuke, downside is that you expose your engine. 

And get much brighter for any type of homing weapon. Also you can't maneuver.

[DDE]

3 hours ago, kerbiloid said:

Also the rocket doesn't need to fly right into the ship. It can shoot sideways on fly-by.

https://en.wikipedia.org/wiki/Explosively_formed_penetrator

(It's a vacuum. The rocket may fly with the axis perpendicular to the velocity when its booster ends working and shoot from the closest point of trajectory directly into the ship.)

Don't bother with the disclaimer in the brackets. This thing is used in a decidedly non-vacuum environment:

Edited July 8, 2020 by DDE

[kerbiloid]

As well, this one

Spoiler

 

and the airborne ones.

But in vacuum they even don't need to rotate, it can just fly with side first and nose to target.

 

[WestAir]

5 hours ago, KSK said:

Sorry if I came on a bit strong with that post.

Comments about writers are a bit of a personal sore spot, having seen a few too many opinionated posts on this forum (which were far less polite than yours) castigating writers and other artists for what they should or should not be.
 

That’s no excuse though - I need to back down a bit.

I actually enjoyed your post. Some people are offended at being educated; I'm just happy you took time from your day to educate me. Keep it up!

[kerbiloid]

Of the lasers vs mirrors.

Even Niven...
https://en.wikipedia.org/wiki/Niven's_laws

Quote

Never fire a laser at a mirror.

A strange thing. Some well-known Russian Vocabulary of Fiction (from 1990s) gives an extended version, referencing to Larry Niven. (but gives no prooflink).

Quote

LASER BATTLE TACTICS - “Remember: 1) the longer the beam’s action, the deeper the cut; 2) in the event of an attack by superior enemy forces, rapid movements should be made, cutting the flesh shallow to restrain the attacker's pressure; 3) always aim at the body; 4) do not allow too close contact with the enemy; 5) never aim in the mirror (including reflective armor) ; 6) clothes of the same color as the beam of your laser are no less dangerous than reflective armor ", (L. Naiven ) .

I guess, a bush of tomatoes is the best anti-laser protection. The leaves from green, the fruits from red.

Edited July 8, 2020 by kerbiloid

[Scotius]

*sigh* That high-temperature fabric superconductor sure would be nice to have.

[kerbiloid]

And I guess, if send a relativistic beam of neutral deuterium atoms, they should probably also do fusion on contact.

Also, N2D4 contains more hydrogen ratio per total mass than usual hydrazine.

Edited July 9, 2020 by kerbiloid

[StrandedonEarth]

On 7/8/2020 at 1:51 PM, Scotius said:

*sigh* That high-temperature fabric superconductor sure would be nice to have.

Or a reasonably compact power source that can power a continuous zettawatt laser. And a zettawatt laser capable of continuous operation, of course., of course.

Now how much thrust would that provide...?

Edited July 10, 2020 by StrandedonEarth