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The Physics of Space Battles 
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Post The Physics of Space Battles
An interesting article on iO9 on speculating on the topic of what space battles could look like in real life by Joseph Shoer, an aerospace engineer studying modular spacecraft assembly.

http://gizmodo.com/5426453/the-physics-of-space-battles?utm_campaign=socialflow_io9_facebook&utm_source=io9_facebook&utm_medium=socialflow


Sat Mar 05, 2016 11:10 pm
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Post Re: The Physics of Space Battles
He leaves out a description of what mines would actually be: torpedoes/missiles waiting on long-term standby for a target, using ion drives & the like for swarm-keeping. Also skipped (at least from my perspective) is that a small fighter can obtain the same hit-chance at a closer range than a capital ship, due to both cross-section and maneuverability.

Also, if you can afford to mount an invasion of Mars, complete with insertion jumps, then you can afford to relay power from a capital ship to a recovery shuttle. I don't believe that can supply all of your thrust, but you should be able to get a decisive boost without significantly increasing your mass (you say "but the heat!", and I reply "make the emitters disposable and integrate them into the propellant!"). Also, they're probably going to have some launch infrastructure on-world: I've always been a bit leery of laser-based (though I guess that could be a practical technique to transfer launch energy from orbit to the surface: just remember to deploy a mirror array before recovery operations begin), but I understand that Olympus Mons extends out past the greatest bulk of the Martian atmosphere, so maglev launch boost is something that they'll probably be using.

Incidentally, once things get to "Invading Mars" levels, I think heat will be less of an issue than we normally think, at least for capital ships: if you can find a way to transfer your ship's heat into a plasma magnetically (some speakers apparently already use magnetic heat transfer into ferrofluids, but plasma is actually hotter so I doubt it to be as easy), then you can probably unfurl a magnetically-confined plasma sail for your radiators, while keeping mass-loss low enough to actually take advantage of it. There have also been some mentions that I've seen recently of cheating at thermo-dynamics, by pre-pumping a lasing medium to almost it's lasing point, so that heat energy is enough to knock it over the lasing-cliff.


Sun Mar 06, 2016 3:25 am
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Post Re: The Physics of Space Battles
http://gizmodo.com/5426453/the-physics-of-space-battles
for a shorter version of the link. You surely clicked it on fuckbook?

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Sun Mar 06, 2016 9:47 am
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Post Re: The Physics of Space Battles
hi hi

It's a pretty rudimentary look at the physics, and gets a few things wrong. And oh my, I made the mistake of looking in the comments. :shock:

There is nothing about a small fighter that makes it more maneuverable than a larger ship, given proportionally sized maneuvering drives. With multi-spectrum imaging, having radar reflecting surfaces and a small cross-section is not going to be as great a help as one might think. Already, even in Earth's crowded orbit, military space experts are finding that it is possible to keep an eye on every threat larger than a fleck of paint.

The moment couple force will allow people to put gyroscopes anywhere on a space craft, not just its center. Probably more than one smaller gyroscopes than one big one, in case one fails. Also, gyroscopes that allow you to turn quickly are going to eat up a large chunk of your payload budget. I suspect that turreted weapons will be more utilized than pointing the spacecraft's nose in the direction of fire. (Gyroscopes are just as big a weakness as gimbals. If one of them is hit, your space fighter will likely experience the fascinating phenomenon known as explosive delamination.)

We have laser weapons today. I highly doubt we will be using guns in space, due to their abysmal range and velocity. And anyone invading Mars is either going to be going up against an undefended, primitive colony, or they'll have to worry about being shot at the entire way by their gigantic ground based lasers, which make use of the wonderfully thin atmosphere.

And because I looked at the comments, I have to add that Ion engines do, in fact, have physical limits that prevent them from being scaled up. The biggest limit is voltage, if you try to pump too much voltage into the engine, you get arcing, which is going to ruin your day.


Sun Mar 06, 2016 12:47 pm
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Post Re: The Physics of Space Battles
icekatze wrote:
And oh my, I made the mistake of looking in the comments. :shock:
Did you notice the one about Meson weapons? I found that a rather interesting idea.

icekatze wrote:
There is nothing about a small fighter that makes it more maneuverable than a larger ship, given proportionally sized maneuvering drives.
And yet I suspect that small-craft and capital-ships will usually not have matchingly-proportional maneuvering drives, due to optimizations for their strengths & weaknesses.

Also, proportional to what: mass/volume or surface area?

icekatze wrote:
I suspect that turreted weapons will be more utilized than pointing the spacecraft's nose in the direction of fire.
I suspect that all dumb-mass & conventional beam weapons will be at least pintle-mounts for the sake of hitting anything more maneuverable than an asteroid. Turrets, I think, would depend on both weapon & ship, since turrets are basically by definition heavier than pintle mounts.


icekatze wrote:
We have laser weapons today. I highly doubt we will be using guns in space, due to their abysmal range and velocity.
Armor. Lasers will be used, and will work, but you will use as much armor as you think you need to keep your ships combat-effective, which I suspect will mean the ability for capital ships to come within kinetics-range of each other (by which point both will probably be significantly damaged, the kinetics being used as a fight-ender through kill, surrender, or withdraw).

As for types, some armor will be mounted on the hull, and I imagine at least some will be implemented either through nano-sats, or similarly to a mag-sail, just with a tighter sphere & solid materials (the difficulty would be finding an oscillatory system that kept them from clumping together: that would need a bit of research).

icekatze wrote:
And anyone invading Mars is either going to be going up against an undefended, primitive colony, or they'll have to worry about being shot at the entire way by their gigantic ground based lasers, which make use of the wonderfully thin atmosphere.
Construction thought: large hollow tower, actively-damped internal mirrors at top & bottom, energy pumps running along the tower's internal wall, with focusing optics partially at the top of the tower, and partially on the ground surrounding the tower, sort of like a reverse solar power tower. With a big enough mirror array, you could theoretically focus all the way to Earth orbit.

icekatze wrote:
And because I looked at the comments, I have to add that Ion engines do, in fact, have physical limits that prevent them from being scaled up. The biggest limit is voltage, if you try to pump too much voltage into the engine, you get arcing, which is going to ruin your day.
As I best recall, building outwards counters that by allowing more current at the same voltage. Roughly equivalent to just strapping on a second Ion engine. Also, I imagine that you can probably do staging in some way, obtaining higher mass flow at the cost of more power, AND a physically longer engine.


Sun Mar 06, 2016 10:07 pm
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Post Re: The Physics of Space Battles
hi hi

I didn't see the one about Meson weapons, and while they're great science fiction in the Traveler universe, they unfortunately would never work in real life, for a number of different reasons. (First, pi-mesons don't decay all at the same time, they have a half life, so only a small fraction of your weapon will go off inside the ship. Second, in order to get the kind of range you would get out of a particle beam weapon, you'd need to fire them at a ridiculously close to the speed of light velocity, to the point where a particle beam would be vastly more effective.)

I think you're right about small-craft and capital-ships not being proportional. I suspect that capital ships will be faster. They'll have better mass ratios on armor, minor systems can stay small while on a smaller craft, gauge limits will prevent them from miniaturizing endlessly, and bigger ships will have bigger apertures, letting them fire from further away, or more frequently with better heat dissipation.

I would put my money on missiles rather than unguided munitions for kinetic weapons.


Sun Mar 06, 2016 10:23 pm
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Post Re: The Physics of Space Battles
I see smaller ships being more manoeuvrable.
If you make a fighter agile, you need to strengthen its chassis against the forces coming from fast rotations/turns.
Doing that with capital ships means unnecessary heavy bulkheads to stabilise the big ships for rotation.
Use big bulkheads for the main acceleration lines (front to back, or "up to down" under acceleration as felt inside), but not for turning stability.
With fighters you'll stabilise all directions, much more mass put into the structure compared to capital ships, which will likely avoid turning during a battle, as that would present the big broad sides to the enemy. Keep your nose to the enemy if you're taking damage and hope you kill him before he sends his killing shot. And that you've accelerated past him before something really nasty happens. Turn then, if necessary, or flee while he still needs to turn, decelerate, and accelerate again to pursue you.

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Mon Mar 07, 2016 2:37 am
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Post Re: The Physics of Space Battles
hi hi

Maybe if someone is making a capital ship that is kilometers in length, there will be heavy bulkheads involved, but really the structural capabilities of steel are more than up to the task of supporting reasonably sized vessels.

If space ships are made roughly spherical in shape, or perhaps more likely cube shaped, there's not going to be much of a broadside to present to an enemy.

The discussion in the article was largely about space combat using orbital mechanics. Turning and fleeing, and pursuing is not going to be a simple thing when you're using Hohmann transfers. For most attacks, once you leave orbit of your home, you're pretty much committed at that point. If an attacker wants to flee once they've already engaged the enemy, they really don't have any good options to do it. I suppose maybe if you've got infrastructure around Jupiter or Saturn, you could swing out into a wider orbit and maybe drift for a couple of years until someone can get a tanker out to you.


Mon Mar 07, 2016 11:20 am
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Post Re: The Physics of Space Battles
icekatze wrote:
I didn't see the one about Meson weapons, and while they're great science fiction in the Traveler universe, they unfortunately would never work in real life, for a number of different reasons. (First, pi-mesons don't decay all at the same time, they have a half life, so only a small fraction of your weapon will go off inside the ship. Second, in order to get the kind of range you would get out of a particle beam weapon, you'd need to fire them at a ridiculously close to the speed of light velocity, to the point where a particle beam would be vastly more effective.)
The point, I think, was to use them to side-step armor that was effective against your particle (and/or other) beams: something of a specialized weapon, honestly. The main question in my mind is the practicality.

icekatze wrote:
I think you're right about small-craft and capital-ships not being proportional. I suspect that capital ships will be faster. They'll have better mass ratios on armor, minor systems can stay small while on a smaller craft, gauge limits will prevent them from miniaturizing endlessly, and bigger ships will have bigger apertures, letting them fire from further away, or more frequently with better heat dissipation.
I suspect that rather than being "faster", capital ships will have a higher total impulse. Small craft, as you've noted, are going to have difficulties with equipment miniaturization, so they'll be designed to maximize on their unique trait: size. To my mind, this means relatively small total impulse due to the absence of ion or similar engines (at least on combat craft): their engines will be chosen only for combat, because that'll likely be the only place they can obtain an advantage over capital ships (note that I'm assuming that they'll be loaded with laser & particle weapons, and the specific advantage is that a smaller craft can clear it's own silhouette sooner than a larger craft with the same acceleration: they'll have the same chance of being hit at a much closer range).

icekatze wrote:
I would put my money on missiles rather than unguided munitions for kinetic weapons.
Eh, kinetics are kinetics for this model. Missiles will probably work better, but likely you'd carry some "dumb" kinetics for unusual opportunities (or needs, so as scuttling a ship).

icekatze wrote:
Maybe if someone is making a capital ship that is kilometers in length, there will be heavy bulkheads involved, but really the structural capabilities of steel are more than up to the task of supporting reasonably sized vessels.
Give an engineer a cup that's half-full, and they'll say it's twice it's optimal volume. Total mass will matter much more on a dreadnought than on a bulk container transporter, since dreadnoughts are supposed to get shot at.

icekatze wrote:
If space ships are made roughly spherical in shape, or perhaps more likely cube shaped, there's not going to be much of a broadside to present to an enemy.
I'd expect something more elongated, probably 4 or more times longer than it is in diameter. You get more surface area per volume, while reducing your optimal cross-section. To make it better, find some way to mount the primary engines near midships in a vectoring configuration, so that maneuverability is preserved without necessarily giving the enemy a clear shot at your engines.

icekatze wrote:
The discussion in the article was largely about space combat using orbital mechanics. Turning and fleeing, and pursuing is not going to be a simple thing when you're using Hohmann transfers. For most attacks, once you leave orbit of your home, you're pretty much committed at that point. If an attacker wants to flee once they've already engaged the enemy, they really don't have any good options to do it. I suppose maybe if you've got infrastructure around Jupiter or Saturn, you could swing out into a wider orbit and maybe drift for a couple of years until someone can get a tanker out to you.
I would expect (at least for capital ships) a two-drive system: ion drives or similar for "strategic maneuvering", and something closer to chemical thrusts for actual combat operations. You can juke around real nice during combat, but for really getting around you're at the mercy of time.


Mon Mar 07, 2016 9:36 pm
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Post Re: The Physics of Space Battles
hi hi

Quote:
The point, I think, was to use them to side-step armor that was effective against your particle (and/or other) beams
My point was that if you can accelerate a particle to a Lorentz factor of 10^16, then literally no armor will stop it, and using regular particles will ensure that more of the energy will be directed on target. (pi-mesons have a half-life of 0.000000084 nanoseconds, you have to get them going very fast in order to not decay at particle beam ranges.)

The problem with elongated shapes is that they have a higher moment of inertia, although if you had maneuvering thrusters on all corners and were attacking your foe head on, you could maneuver without changing your bearing.

(Even with ion drives, the delta v budget for doing an about face on a planetary transfer is mind boggling. Earth to Moon it's not so bad, but Earth to Mars it is really awful. That being said, I'd expect that warships of that tech level would use the two engine approach as well. Or even better yet, detach the combat module from the interplanetary module. Leave the squishy people on the slow half, and whoever wins the battle can capture the other side's slow modules.)


Mon Mar 07, 2016 11:10 pm
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Post Re: The Physics of Space Battles
Krulle wrote:
http://gizmodo.com/5426453/the-physics-of-space-battles
for a shorter version of the link. You surely clicked it on fuckbook?


I did. But I copied the link from the website that opened up. Didn't know you could get a shorter one, I just thought that was the actual link itself. :?


Mon Mar 07, 2016 11:20 pm
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Post Re: The Physics of Space Battles
icekatze wrote:
The problem with elongated shapes is that they have a higher moment of inertia, although if you had maneuvering thrusters on all corners and were attacking your foe head on, you could maneuver without changing your bearing.
Assuming that you can fight at anything beyond "knife"-range, your ships will spend a very long time attacking your enemy head-on. Until you get to impractical accelerations like the Loroi, ranges where your turning speed matters are likely to be either mopping-up actions, or high-speed jousts.

And since you mostly just need to maneuver in the plane perpendicular to your heading, I think that placing most of your thrust assets on gimbals (or something) surrounding your center-of-mass would work out fairly well.

icekatze wrote:
(Even with ion drives, the delta v budget for doing an about face on a planetary transfer is mind boggling. Earth to Moon it's not so bad, but Earth to Mars it is really awful. That being said, I'd expect that warships of that tech level would use the two engine approach as well. Or even better yet, detach the combat module from the interplanetary module. Leave the squishy people on the slow half, and whoever wins the battle can capture the other side's slow modules.)
I've thought about such things before. The slow-side is obviously going to be vulnerable, but for patrol craft I think it's absolutely the right route to take (note: I was thinking solar sail + inertial gravity ring on one side, & orion-drive + short-haul gunship on the other). Realistically though, I think it could be argued that this is also the basic formula that carriers follow, I just assume that you'll probably have (really big) weapons on the slow-side as well.


Tue Mar 08, 2016 11:00 pm
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