Physics of space battles - gizmodo article

[drsid]

I found this interesting article, that I thought might be of interest/use to those creating hard sci campaigns:

 

http://gizmodo.com/5426453/the-physics-of-space-battles

[Curufea]

Re: Physics of space battles - gizmodo article

 

I've seen a reference to this article before. In context of the thread it was "in summary the wargame we are in the forum of does all this". The wargame being Attack Vector: Tactical

[Nyrath]

Re: Physics of space battles - gizmodo article

 

I hate to tell you this but you've been scooped.

http://www.herogames.com/forums/showthread.php/77323-An-interesting-article-on-the-Physics-of-Space-Combat (December 18th, 2009)

[The Weapon]

Re: Physics of space battles - gizmodo article

 

"A definite downside to kinetic weapons on a starfighter is that they would impart momentum to the fighter or change its mass properties. Very large cannons or missiles might therefore be impractical, unless the fighter can quickly compensate for what is essentially a large rocket firing. Even that compensation might give the enemy just the window he needs…"

 

For big cannons fair enough but why would missiles change the velocity? Kinda disqualifies them AFAIC.

[austenandrews]

Re: Physics of space battles - gizmodo article

 

A large missile leaving the ship, even slowly, imparts movement in the opposite direction.

[dmjalund]

Re: Physics of space battles - gizmodo article

 

A large missile leaving the ship' date=' even slowly, imparts movement in the opposite direction.[/quote'] yes, but the moment it disengages it stops imparting momentum, so it can impart very little momentum if it disengages early

[Xavier Onassiss]

Re: Physics of space battles - gizmodo article

 

The other side of the equation is that launching a large missile will reduce the fighter's mass, improving its performance to a degree.

[austenandrews]

Re: Physics of space battles - gizmodo article

 

yes' date=' but the moment it disengages it stops imparting momentum, so it can impart very little momentum if it disengages early[/quote']

Assuming the rocket exhaust doesn't push the ship. It really depends on the relative masses of the missile and the ship. If the missile is tiny by comparison, then the fighter can quickly compensate, as the article says. If the missile is large, then it has to move slowly or it'll send the ship in the opposite direction and require much greater compensation. A missile with a slow disengage time would presumably have reduced utility. Which isn't to say you can't make all the adjustments, just that they have to be made.

[pming]

Re: Physics of space battles - gizmodo article

 

Hiya.

 

Why not have the missile be simple "let go" from the ship via, say, magnetic force (like a railgun sort of thing), then, once the missile is free of the ship, it fires it's rocket? That's how I'd build them if I was making missiles to fire from a ship in space...

[dmjalund]

Re: Physics of space battles - gizmodo article

 

disengaged missiles don't really push back with the exhaust - the exhaust is a gas, it disipates too quickly, and most starship aren't exactly designed to catch gas (like having sails)

[Curufea]

Re: Physics of space battles - gizmodo article

 

Well put.

 

Not to mention the technology of the engine on the missile is likely to be equivalent to the vehicle launcing it. If the spaceship has FTL - the missile will likely have FTL too.

[austenandrews]

Re: Physics of space battles - gizmodo article

 

Why not have the missile be simple "let go" from the ship via' date=' say, magnetic force (like a railgun sort of thing), then, once the missile is free of the ship, it fires it's rocket?[/quote']

If you push the missile in any fashion, you'll get pushback. If the missiles were mounted on a winglike structure or fired from tubes, where the initial exhaust vents away from the ship, then you'd probably be okay.

 

disengaged missiles don't really push back with the exhaust - the exhaust is a gas' date=' it disipates too quickly, and most starship aren't exactly designed to catch gas (like having sails)[/quote']

The blowback thing was a random comment. I'm talking about conservation of momentum.

[dmjalund]

Re: Physics of space battles - gizmodo article

 

until the missile starts its rockets, it has no momentum (momentum = mass x velocity, velocity = 0, therefore momentum = 0)

[austenandrews]

Re: Physics of space battles - gizmodo article

 

until the missile starts its rockets' date=' it has no momentum (momentum = mass x velocity, velocity = 0, therefore momentum = 0)[/quote']

The missile and the ship have momentum as a unit. If the missile goes one direction, the ship goes in the opposite direction. If you can detach the missile close to the ship without imparting much movement, though, it should be simple to compensate. Or arrange it so that the opposing momentum pushes the ship in a desired way.

[dmjalund]

Re: Physics of space battles - gizmodo article

 

The missile and the ship have momentum as a unit. If the missile goes one direction' date=' the ship goes in the opposite direction. If you can detach the missile close to the ship without imparting much movement, though, it should be simple to compensate. Or arrange it so that the opposing momentum pushes the ship in a desired way.[/quote']

let me rephrase that, the missile has no RELATIVE momentum, therefore, since, compared to the ship, it is not going forward or backward, this will have no affect on the ships velocity compared to ANY frame of reference. so the only effect on the ships momentum is the change of mass of the system.

[austenandrews]

Re: Physics of space battles - gizmodo article

 

I'm pretty sure we're saying the same thing.

[The Weapon]

Re: Physics of space battles - gizmodo article

 

Assuming the rocket exhaust doesn't push the ship. It really depends on the relative masses of the missile and the ship. If the missile is tiny by comparison' date=' then the fighter can quickly compensate, as the article says. If the missile is large, then it has to move slowly or it'll send the ship in the opposite direction and require much greater compensation. A missile with a slow disengage time would presumably have reduced utility. Which isn't to say you can't make all the adjustments, just that they have to be made.[/quote']

 

The rocket exhaust can melt steel, if it pushes your ship the weapons manufacturer has a lot of explaining to do. If you are pushing it out a hole (instead of just having iton rails) then moving a missile 1/4 the mass of the rest of the ship it 10m in .01 seconds gives a 50 m/s velocity to the ship. That's slower than a NASCAR racer. There is no significant velocity added to the ship.

[austenandrews]

Re: Physics of space battles - gizmodo article

 

The rocket exhaust can melt steel' date=' if it pushes your ship the weapons manufacturer has a lot of explaining to do. If you are pushing it out a hole (instead of just having iton rails) then moving a missile 1/4 the mass of the rest of the ship it 10m in .01 seconds gives a 50 m/s velocity to the ship. That's slower than a NASCAR racer. There is no significant velocity added to the ship.[/quote']

Well yeah, if you count 50 m/s as insignificant, then it's insignificant.