The physics of space battle

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Re: The physics of space battle

Post by Kackling Kobold on Thu Oct 18, 2012 9:33 pm

Ok so according to my brother, even if your sling had a solid arm, the craziest motor could not turn it faster than the speed of sound through that medium. (the speed that sound travels through whatever the arm is made of).

I dont understand why, but if that's true, your sling is doomed to be a subsonic weapon, & doesnt even compare to modern gunpowder/ C4, let alone a half descent massdriver.


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Re: The physics of space battle

Post by Kackling Kobold on Thu Oct 18, 2012 9:39 pm

Abstractness wrote:If you have accuracy problems, I suggest to put small rocket motors on the projectile, to correct its trajectory.

Putting rocket motors on a near light speed projectile is...

well i dont know... it could be useful I suppose if the distance to your target were measured in Astronomical Units, but how do you tell the projectile it's off course when it's already moving at speeds comparable to your own sensors/ communications. Even if it were relying on its own sensors for the correction, how would a device experiencing the time dilating effects of relativistic speeds know where it's target is, let alone whether it's course needs correcting.
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Re: The physics of space battle

Post by Kackling Kobold on Thu Oct 18, 2012 9:58 pm

Lastly, at "melee range" which I know I know, is ridiculous in space, your sling does... well... nothing, while a mass driver turns a target inside out, all with zero kick.

How many other weapons can brag zero kick; technically even a laser has a kick; not much, but enough that some sci-fi's feature engines based on it. With a mass driver the only kick is from the gravity influence of the mass you're dropping away from you (pulling you forward a tiny bit).

The biggest problem/ drawback to putting a massdriver on a ship, is safety; how do you shield your own ship against the tidal effects of that weapon.
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Re: The physics of space battle

Post by the-anger on Thu Oct 18, 2012 10:41 pm

no projectile can brag zero kick - that would violate newtons 3rd law regardless of the force.

anywho, a mass driver (if it works like i think it does) will have kick equal and opposite to whatever it accelerates, and it depends on the mass ratio of the projectile to the mass driver how great of a kick that would be. idk myself, but something to think about...
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Re: The physics of space battle

Post by Vonstapler on Fri Oct 19, 2012 6:03 am

I read an article a while ago about a French lab that had designed a railgun that actually used the friction created by firing the gun to accelerate the projectile. I read it a long time ago, so I'm not certain on the details, but it was an interesting work around, though they still needed to replace the rails ever 3-4 shots.
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Re: The physics of space battle

Post by Abstractness on Fri Oct 19, 2012 2:05 pm

Kackling Kobold wrote:
your sling idea is problematic at best. By turning the sling, you also turn the ship in the opposite direction, affecting everything inside.
You're right. But there's a simple solution to this: use four slings at the same time. two slings turning into the opposite direction of the other two slings. That's what I was thinking of.



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Re: The physics of space battle

Post by Kackling Kobold on Fri Oct 19, 2012 2:48 pm

Abstractness wrote:
Kackling Kobold wrote:
your sling idea is problematic at best. By turning the sling, you also turn the ship in the opposite direction, affecting everything inside.

You're right. But there's a simple solution to this: use four slings at the same time. two slings turning into the opposite direction of the other two slings. That's what I was thinking of.

Interesting, though a little research reveals any mechanically hurled projectile would indeed be doomed to subsonic projectile speeds, so... not as usefull.
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Re: The physics of space battle

Post by Kackling Kobold on Fri Oct 19, 2012 3:08 pm

the-anger wrote:no projectile can brag zero kick - that would violate newtons 3rd law regardless of the force.

anywho, a mass driver (if it works like i think it does) will have kick equal and opposite to whatever it accelerates, and it depends on the mass ratio of the projectile to the mass driver how great of a kick that would be. idk myself, but something to think about...

In the case of a mass driver, your ship is not exerting any force on the projectile. you are simply creating a very intense gravity field & the projectile falls through it. Granted this kind of assumes your artificial gravity technology has the ability to create a uni-directional field of gravity, which defies Newtonian physics in the first place. This does recall my question about shielding the ship itself though, either you need an equal amount of gravity going the opposite way somewhere on this ship to anchor it, or somehow be shielded against the drag of the same gravity field that's throwing the projectile, both simple to state, but preposterous given the forces implied. The limitation on a mass driver might be structural.

So, apparently it didn't work the way you thought, because no, there would be no kick. A sufficiently wide enough mass driver could hurl asteroids with no course correction needed by the ship or station housing it.

In the case that you could not create a unidirectional field of gravity, it might still be possible to create wells of gravity to sling shot projectiles around, which can achieve mind-bending supersonic speeds as well, though likely not the significant fractions of the speed of light that a "traditional" mass driver would. This weapon too, would have no kick.

Another good question though, how much electricity do these gravity techs consume? Quite possibly too much.
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Re: The physics of space battle

Post by Abstractness on Fri Oct 19, 2012 4:03 pm

Kackling Kobold wrote:
Ok so according to my brother, even if your sling had a solid arm, the craziest motor could not turn it faster than the speed of sound through that medium. (the speed that sound travels through whatever the arm is made of).

I dont understand why, but if that's true, your sling is doomed to be a subsonic weapon, & doesnt even compare to modern gunpowder/ C4, let alone a half descent massdriver.
That's true for a slingshot, but not for a sling. Probably your brother confused "sling" with "slingshot".
Kackling Kobold wrote:
Interesting, though a little research reveals any mechanically hurled projectile would indeed be doomed to subsonic projectile speeds, so... not as usefull.
That's only true if you hurl the projectile on a straight line, which my sling does not. So this would not be a problem.
But the problem with my construction is: the speed of the projectile grows logarithmic. This means it takes very long to achieve high speed.
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Re: The physics of space battle

Post by Kackling Kobold on Sun Oct 21, 2012 3:59 am

right... because the sling does not have a solid arm & is utilizing centripital force & widening orbits, not a straight mechanical translation. You still have an incredible wind up time just to reach supersonic speeds.

How accurate do you suppose that weapon could be.

One of the biggest challenges for space battles is rectifying likely differences between sensor range and weapon accuracy range. The tendency is to want to open fire as soon as you see them an enemy, in some cases this is just impossible. Sure your projectiles go on forever, but whats the point of shooting a projectile at a spaceship with any maneuverability if that projectile has a 2 hour delivery time?

For instance, it *might* be possible to detect artificial gravity anywhere in the gravity well of the same star; creating the possibility to detect enemies many AU away. Light travels one AU in ... i don't recall if its neatly 5 min, or if it was 8 minutes. So at those ranges even a weaponized laser may not be fast enough that you don't have to lead them, and that's assuming you don't have to worry about bloom & spread, which over those ranges; you do. Space is not quite as perfectly empty as we like to think.
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Re: The physics of space battle

Post by Loki on Sun Oct 21, 2012 8:33 am

Kackling Kobold wrote:Light travels one AU in ... i don't recall if its neatly 5 min, or if it was 8 minutes.

~8 minutes.
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Re: The physics of space battle

Post by Zhaky on Sun Oct 21, 2012 12:25 pm

Hey just found this "article" on space maneuvering, it goes a bit more into depth with the maneuverability in space pirat

Hey, it doesn`t move like an aircraft!

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Re: The physics of space battle

Post by Abstractness on Sun Oct 21, 2012 8:06 pm

Zhaky wrote:Hey just found this "article" on space maneuvering, it goes a bit more into depth with the maneuverability in space pirat

Hey, it doesn`t move like an aircraft!

The physics of moon breakers is more like that of small submarines which can roll.

when I was 17 I wrote this little 2D-simulation of a space ship: https://skydrive.live.com/redir?resid=C610EA8B34D914B2!315&authkey=!ALF4Yfm9-0bkplU
Download "Testschiff.swf". If you start it, you should see a white screen with a small orange spaceship. First try to get a feeling of how the ship turns, by using the left and right arrowkeys. if you push the up key the main engine of the ship burns. if you fly outside the screen you probably never come back. refresh the page if that happens. the ship can only accelerate forward, this means you have to turn it 180° to break down using the main engine. have fun
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Re: The physics of space battle

Post by Loki on Sun Oct 21, 2012 9:18 pm

It's like asteroids on steroids but with less shooting lol

I also agree with your analogy; Moon Breakers always made me feel more like I was driving a boat than a space ship.
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Re: The physics of space battle

Post by Abstractness on Sun Oct 21, 2012 10:51 pm

Later I added a planet: https://skydrive.live.com/redir?resid=C610EA8B34D914B2!316&authkey=!APlVQSmxe0hiZwc
it's the same ship but with a much weaker main engine. At the beginning you're falling trough the planet. try to get into an orbit around the planet. the physics is realistic, except you fly trough the planet.
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Re: The physics of space battle

Post by Seelenlos on Mon Oct 22, 2012 3:58 pm

Hi,

First sorry for the terrible english, but I think you should understand the techniques:

I have read about this in 2 Sci Fi Novel (can't remember the names).

In one the Idea was to make atom bomb in a shell with a reflective matter. That way they could focus the gamma ray to kill the crew of the enemy.

It was a one way trip for the defenders ...

In the other book, they also discussed it like your url-Link.
The conclusion:
1. Metal-Balls fired like a shotgun at enemy (accelerated). (wide area shootings)
2. Accelerating asteroids with rockets to enemy (pure rockets could also be shoot down with defensive shotguns). Asteroids can take a lot of punch to be destroyed.
3. Laser Beams to for pinpointing special enemy equipment.
4. Ramming with special constructed ships

On a planetary basis they use atom bombs to accelerate plate over missile silos.

What I saw in a sci fi film "Firefly" was also very interesting: ropes! But that is another story...

So much to the praxis.

The rest is Theory! and a thick hull.

regards
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Re: The physics of space battle

Post by Nightwing on Mon Oct 22, 2012 5:05 pm

I love seeing a thread that goes into technical details like this one does...

Seelenlos wrote:What I saw in a sci fi film "Firefly" was also very interesting: ropes! But that is another story...

Firefly? You are my hero. I don't know of many people that have seen that show before it was prematurely cut...
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Re: The physics of space battle

Post by Loki on Mon Oct 22, 2012 5:11 pm

After making Cabin in the Woods and The Avengers, Whedon would get approval in a heartbeat to pick up that project again. If he wanted to...
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Re: The physics of space battle

Post by Peelark on Tue Oct 23, 2012 4:33 pm

The biggest problem with spaceships that we've encountered so far is energy storage.
If we could design energy generators/storage units that were more efficient at carrying useful fuel than batteries or rocket propellent.
However, even then, the issue with mechanical projectiles is that the number of them that you can take on board is limited.
I think lasers are going to be the ultimate weapon in space - but not those crazy short pulsed visible green slugs that you see in the Hollywoods!!
The lasers on future spaceships will be microwave frequency (so MASERS, technically) and will fire a continuous, broad beam of light, locked onto enemy ships for a few seconds, just long enough to melt the outer shell and cause a gas rupture, blowing the pilot's brains out with his own body's pressure. Mmmmm!

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Re: The physics of space battle

Post by Abstractness on Wed Oct 24, 2012 12:36 am

but visible light has greater range than microwaves. wavelengths:
green light: 550 nm
microwaves: 1 mm to 30 cm
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Re: The physics of space battle

Post by Kackling Kobold on Wed Oct 24, 2012 5:52 am

mass drivers and space slings alike could harvest projectiles from asteroids.

Mass drivers wouldn't need to; if you had gravity technology sufficient to make a mass driver, you also have a "cheap" engine for getting things into orbit/ back to ground without cumbersome heat shielding & prohibitive fuel.

microwave lasers are relatively easy to armor and/ or shield against, & it's the same kind of shielding that a spaceship needs to ward off the harmful presence of a star. A relatively powerful magnetic field around the ship would greatly depreciate incoming fire. They are also broken down somewhat by solar wind... though not enough to limit their range within the confines of a star system.

As for energy storage?
I think the future of space involves finding ways to harvest the energy that's already out there. It's all around a spaceship, it's the most abundant thing in space besides vacuum. Just making a ship habitable requires huge amounts of shielding just to deal with it; why not use some of that to power the ship?


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Re: The physics of space battle

Post by Abstractness on Wed Oct 24, 2012 11:14 pm

range of lasers or masers

Here you see how a beam loses its Intensity: http://en.wikipedia.org/wiki/File:Wave_Diffraction_4Lambda_Slit.png

d = diameter of our laser or maser beam
λ = its wave length
r = d/2
I(x) = Intensity at distance x in front of our weapon.

If x < r²/λ then I(x) ≈ I(0)
If x > r²/λ then I(x) ≈ (r²/(λx))² I(0)

Example1:
If we use a maser beam with d=1m and λ=1cm
and shoot a target at distance x=10km,
the beam hits 160'000 times less intense than when it left the weapon.
This means masers are useless.
Example2:
If we use a laser beam with d=1m and λ=500nm
and shoot a target at distance x=10km,
the beam hits with almost the same intensity as when it left the weapon.
Our laser could also hit targets at about r²/λ=500 km distance.
This means visible lasers are usefull.


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Re: The physics of space battle

Post by Kackling Kobold on Thu Oct 25, 2012 2:14 pm

I always thought microwave weapons necessitated a dish... thus the "barrel" size would be several meters, assuming the dish focused the microwaves into a beam, rather than onto a point.

Focusing onto a point might greatly improve range given the Wave Diffraction cited by abstractness, but it would have the problems of giving the weapon a narrow effective range, eliminating the flexibility it would need as a combat weapon.

Even given abstractness's misgivings, masers might make an amazing defense system against warheaded projectiles.

I wouldn't write masers off as useless, Tesla proved otherwise in the 30's, but in space I would tend to discount any weapon whose maximum range is not measured in mega-meters as a defensive or last ditch measure, & would be nervous with anything that could not reach at least 1 AU, sensor and targeting issues aside.

what about x-ray lasers?



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Re: The physics of space battle

Post by Abstractness on Sat Oct 27, 2012 3:42 pm

A hard Xaser still hits at r²/λ = 25 Gm < 1 AU. Where diameter=1m
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Re: The physics of space battle

Post by Kackling Kobold on Mon Oct 29, 2012 1:00 pm

Abstractness wrote:A hard Xaser still hits at r²/λ = 25 Gm < 1 AU. Where diameter=1m

ok so 250 mega meters is certainly useful for tactical ranges even by my standards, though the beam is probably only combat effective (can meaningfully damage another vessel) for about 3/4 that range.

For quick reference, the diameter of the earth is approximately 12 mega meters, the diameter of the moon is 3.4 M & the orbit range of the moon varies from 356 M to 406 M.

So if your laser is only combat effective for 187 M and you're orbiting the earth at 2 M you still come up at least 160+ M short of being able to hit targets orbiting the moon.

Most sci-fi assumes we would be able to detect incoming enemies from at least that far away (and thats if their sneaking up from behind the moon).

I hope you start to understand why I insist that range in space is king.

what I really wanted to know though, Abstractness, was your opinion on the usefulness of x-ray lasers vs. visible lasers.

I may be showing my ignorance on the subject, but I'm also not clear on the difference between infra-red lasers and "Masers". My understanding is that they're both off visible light in the same direction, but one is much further from the visible scale?

Most of the research I had to do for sci-fi storytelling had to do with ion & plasma technology, both certainly fascinating and more real than we tend to think.

As for hitting targets at strategic ranges as distant as 1 AU, sounds like we may be limited to more exotic weapons; near light speed projectiles, variously propelled asteroids, or some sort of inter planetary cruise missile, and for the most part hope the target is big and/ or not moving too erratically.
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Re: The physics of space battle

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