Official "Discuss the latest page" thread

All discussion related to the Crimson Dark webcomic (at crimsondark.com)
macnut
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Re: Official "Discuss the latest page" thread

Post by macnut » Sat Oct 13, 2018 2:25 am

There's a very nasty thing about railgun rounds though, that probably limits their use by other military forces. Energy beams will generally dissipate over time and distance - they tend to spread out and become probably no more harmful that a flashlight beam over millions of kilometers. A railgun round on the other hand, especially one fired at a significant percentage of the speed of light, will keep right on going if it misses its target (sometimes even if it doesn't - it may punch right through and keep going). In open space that's not much of a problem, but near planets and space stations, well, those rounds become instruments of collateral damage.

Put simply, a lot of the rounds fired at our protagonists over the last two pages are likely to end up slamming into the station or the planet below. Even the ones fired into open space will be a potential navigational hazard to any incoming ships for some years to come. Remember, they don't dissipate, they just keep going until they hit something solid enough to stop them.
The MacNut
Writer and Artist of The Vanguard, a space opera superhero webcomic.

CorvusCorax
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Re: Official "Discuss the latest page" thread

Post by CorvusCorax » Sat Oct 13, 2018 10:15 pm

This is quite an interesting dilemma, not just for railgun rounds but also for the point defense cannons (and the shrapnel they cut loose as they hit, though the latter also goes for the debris created by explosions from the energy weapons)

It doesn't matter at all in deep space. In interplanetary or even interstellar space, bullets and debris will keep going in a straight line for ages, and within months will be so far separated from each other that their impact risk on anything is not higher than that of any other micrometeorites. Space isn't empty, there's always stuff flying around at thousands of meters per second, in sizes from a dust particle to a small pebble that impacts on other stuff all the time. Look at all the craters on the moon. Whats important is that the density of the stuff is not significantly increased, so also the impact risk is not.

Railgun shots at relativistic speeds have the advantage that they are always going at above escape velocity. They will not remain in orbit around the planet. If they hit the atmosphere they will explode on entry and turn into a harmless plasma ball, long before they strike anything solid. So if they miss the station, the risk that they hit anything before leaving the solar system and going for interstellar space is very low.

They are below light speed though. It will be many hundreds of years before they get even near the next star, many thousands of years until they have a real certainty of impacting anything, and most likely that anything will be an asteroid, moon, comet, or a star and completely uninhabited.

They also can't keep going at relativistic speeds for ever. Collisions with gas molecules and dust particles in the interstellar medium and the blue shifted light pressure from the front versus red shifted in the back, will slow them down over thousands of years.

Last but not least, they might be fast enough to escape the galaxy they were fired in, which gives them billions of travel time before they would impact anything ever.


So the main thing one has to worry about is "slow kinetic projectiles" fired from kinetic point defense cannons, as well as debris of all kind, broken loose by impacts from both kinetic and energy weapon impact, if these happen in low or medium orbit around a planet.

Here the gravity pull of the planet will keep them trapped in the gravity well for many decades, and by the nature of orbital mechanics, although each particle has its own orbit, they all intersect with the orbit they were originally fired or broken loose from.

This means, each and any bullet, piece of debris, or even just shed loose bullet casing or paint particle is on a potential collision course with this space station hub.

Each impact will create also more debris, again each one in orbits that intersect each other. The phenomena is called Kessler syndrome

Appropriate reference to the movie "gravity" here ;) although they exaggerated a bit ;)

Interesting thing is that the bullets fired retrograde (against the direction of orbit) are very likely to burn up in the planets atmosphere.

In the nasaspaceflight.com forum (sorry I don't have the exact link) someone once asked the question, if an Astronaut on a spacewalk tosses a ball as hard as they could, could they actually put enough momentum on it, that its orbit would cause it to reenter.

The answer was, no. People can't throw that fast. But there wasn't much missing. Hitting the ball with a baseball bat or a golf club would be enough. Even an arrow fired from the ISS in the opposite direction that ISS is moving would be slow enough to reenter the atmosphere.

So its a safe assumption that all bullets fired roughly opposing the orbit of the station, will reenter, burn up in atmosphere and no longer be of any harm to anyone.

Since these ships are dogfighting and firing in all directions, this probably applies to around 1/3 of all the projectiles fired.

The rest will end up on all sorts of orbits with orbital periods in the same range as the station (on an earth sized planets, that'd be between one and two hours) to maybe around twice as much.

and over the next couple of years they will increase the impact risk in low orbit for any vessel flying in orbit around that planet, no matter if civilian or military and no matter which faction.

A single fight will probably be manageable. But if an entire war is fought in orbit around the planet, with large or even multiple space battles, it might indeed turn that orbit into a very very hostile space and trigger a Kessler syndrome for that planet.

In the end whether kinetic weapons are used or not doesn't even matter that much. An exploding spaceship or a station breaking up creates debris on a different order of magnitude.

This is a highly relevant video, visualizing the debris cloud from the 2009 in orbit collision between iridium 33 and Cosmos 2251
https://www.youtube.com/watch?v=_o7EKlqCE20
(in timelapse of course, one orbit around earth takes 90 minutes approximately)

an exploding space station or a larger space battle would create the same kind of mess

CorvusCorax
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Re: Official "Discuss the latest page" thread

Post by CorvusCorax » Sun Oct 14, 2018 6:07 am

Got side tracked with kessler syndrome. What I wanted to say originally is critique on the maneuvering of the Strix class ship in this fight.

Code: Select all

Scenario 1
                                                 __
                                      o---      =o |_
Enemy                         o----            /   |
  /\                                          |    \--.
 / o= --------          -------          -- ###-X      ====<-
<   |                                       \_     /--'
 \ o= ------   ------       ------          --\-X  |
  \/                                           °°°°°^^     
                                               Strix class

Code: Select all

Scenario 2
                                    
Enemy
  /\                                          
 / o= --------          -------        -----  =o_____-----     -----
<   |                                       ###<<HHHHH>====<-
 \ o= ------   ------       ------     ----   =o°°°°°°°----       -----
  \/
                                               Strix class
Or in words: If you have a ship that is both wide in one dimension and relatively narrow in another, its usually a good idea to always show your narrow side towards the opponent

This is relatively difficult in an atmospheric dogfight. The "wide" side is usually your wing surface. It also provides atmospheric lift, which is perpendicular to the surface. As such you need to rotate your wings in order to maneuver. Showing your narrow side to the opponent and circling around the opponent (centipetary force pointing towards the opponent) are contradictory objectives in atmospheric dogfight, you have to trade one against the other.

When fighting in space, any accelerating force comes from the thrusters. Most spaceship have their main thrusters pointing backwards.
Unlike an airplane , which needs to point its nose in flight direction and its bottom towards the direction their accelerating force points to (these are two perpendicular vectors, so the aircrafts orientation in 3d space is always determined) a spaceship has only one force vector to take into account, and thats the acelerating force. The nose needs to point away from the accelerating force to use thrusters at full efficiency.

In case of a dogfight, this is usually a centripetal force, so the nose would mostly point towards the opponent, while the thrusters would ideally point away from the opponent (unless you try to get away from the opponent) More importantly the rotation vector alongside the accel force vector can be freely chosen.

AKA. the pilot can choose his roll vector arbitrarily in order to minimize the chance to get hit.

In case of the strix, which has point defense turrets on both upper and lower side with a relatively wide field of view, a narrow side to enemy orientation would also bring its own guns into good firing positions.

In the scene shown, this is not being done. The Strix class presents a wide target towards the gunboat (and promptly sustains hits)

I can only guess that Ren trained corvette piloting on a vessel that had have a drastically different geometry, such that facing the opponent at a diagonal roll angle would have been more advantagous.

Of course things are more complicated than that. One also has to take into account deflection angles, when dealing with kinetic projectiles.

A projectile that hits the vessel surface at 90° angle is very likely to penetrate fully. A bullet that strikes the armor at a very shallow angle instead, is very likely to ricochet without doing damage. This normally is one more reason to present the narrow side towards the target,

however the Strix is not ending in a knife edge leading edge, but a relatively blunt rectangular "edge" on which any impacts would penetrate at almost perfect 90° angles (and if they did so, might fly through a good portion of Strix internal space, potentially dealing critical damage)
(worst case a bullet would go lengthwise all the way through, making a hole in every bulkhead and every piece of equipment, unless it got stuck halfway through.

Especially if the armor on Strix "narrow" side is exceptionally weak, and the armor on top and bottom of the "wings" is stronger (although that wouldn't be a smart design decisions as far as weight distribution goes) it might actually make sense to face the enemy at a 45 degree angle, in order to protect the potentially vulnerable edges, at the cost of getting relatively localized "shoot throughs" from the bullets that strike the larger upper surface.

I'd be happy to hear some reasoning for this particular piloting. Does Ren really know how to fly this particular Corvette in battle and is protecting a particular vulnerability? Or is she just flying in a more vulnerable position due to inexperience with dogfighting this particular vessel? (Mind you, Corvettes aren't necessarily used for dogfights anyway ;) )

macnut
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Re: Official "Discuss the latest page" thread

Post by macnut » Mon Oct 15, 2018 3:16 am

I'm not sure we should assume that every railgun projectile entering atmosphere will burn up. If these projectiles are dense enough to penetrate warship armor (and all parties concerned in-universe seem to think they at least could be), then they may be dense enough, and therefore tough enough, to get all the way to the ground, even if fired at relativistic velocities. Especially if fired at those velocities, since that those speeds the projectile would take mere seconds to pass through the atmosphere to the ground. Outer layers of the projectile will ablate off during passage through the atmosphere, but enough of it may survive to make a good-sized crater when it hits hopefully empty ground.

I'd like to comment on your excellent commentary on Ren's piloting vs armoring of their corvette, but quite frankly I'm not sure I know enough about either Ren's piloting experience or the location of the best armor on the corvette to answer. All I can tell for sure is that dialogue among the crew before the fight started indicated that they expected to take damage during the battle regardless, and that the final panels of Friday's strip showing the corvette still maneuvering seems to show that damage wasn't critical. So maybe Ren's piloting did the job, and/or the armor held up where it was most needed.
The MacNut
Writer and Artist of The Vanguard, a space opera superhero webcomic.

CorvusCorax
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Re: Official "Discuss the latest page" thread

Post by CorvusCorax » Mon Oct 15, 2018 2:54 pm

macnut wrote:
Mon Oct 15, 2018 3:16 am
I'm not sure we should assume that every railgun projectile entering atmosphere will burn up. If these projectiles are dense enough to penetrate warship armor (and all parties concerned in-universe seem to think they at least could be), then they may be dense enough, and therefore tough enough, to get all the way to the ground, even if fired at relativistic velocities. Especially if fired at those velocities, since that those speeds the projectile would take mere seconds to pass through the atmosphere to the ground. Outer layers of the projectile will ablate off during passage through the atmosphere, but enough of it may survive to make a good-sized crater when it hits hopefully empty ground.
Physically modelling impacts at these velocities ( even just orbital speed impacts, but this also goes for relativistic speeds ) is done by considering both the projectile and the impacted material as a fluid.
The kinetic energies in the area of impact are much higher than the bond energies betwern molecules ( at relativistic speeds even between atoms, possibly even between subatomic particles, after all you are hitting at speeds comparable to those in a particle accelerator )

As such you can model the impact of a railgun bullet on armor / atmosphere as the intersection of a hypercritical fluid streams, or even proton/gluon plasma of varying densities. At these energy levels everything is a fluid.

As the projectile hits, it would not so much penetrate, but fuse with the material it hits in a nonelastic matter, where any material involved is itself accelerated. Like a shock wave.

Like in a tank hit by a shell, most of the damage inside a ship would not be done by particles from the original projectile - at relativistic spees impacts, those would likely have converted to hard radiation at that point - but by matter accelerated by thus shockwave.

Even thick spaceship armor is way too thin for this shockwave to dissipate. You woild simply have matter, lets say 10 times the mass of the original projectile, flying through the interior at 1/10 th the speed. ( which is still tenth of thousands of kilometers per second! ) impacting interior walls and the hull on the other side and creating secondary shockwaves.

It would act like a dum dum bullet. Tiny impact hole, large part of the ship ripped out on the opposite side.


Atmosphere is a different matter. It has only a tiny fraction of the density, but, as before, one has to model the impact as individual impacts vetween particles. Unlike ship armor, the atmosphere is kilometers thick and gets thicker further in/down. This transfers all the energy into a plasma shockwave very quickly which then spreads out over a very large area. It doesm't matter that the atmosphere is lower density than the projectile, since at hypersonic speeds, a shockwave forms in front of the projectile in which the pressure increases until it matches up in density - and beyond.

This shockwave wouldn't be harmless of course. The effect would be comparable to a nuclear bomb, ignited in the high atmosphere, complete with radiation and EMP effects and shattered windows in hundreds of kilometers around the entry trajectory. Not much fallout though, luckily there's not enough mass in the projectile.

A good first order aproximation of a relativistic speed impact can be made by stripping a small nuclear bomb with the same yield as the impactors kinetic energy to the hull and igniting it. Only difference is, the impactor acts more like a nuclear shaped charge, with most of the damage on the opposing side of the ship. ;) You'd also get a similar radiation release.

Firing that at a space station with civilians in it...

"war crime" kinda sums it up ;)

CorvusCorax
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Re: Official "Discuss the latest page" thread

Post by CorvusCorax » Mon Oct 15, 2018 3:14 pm

That being all said, the rail gun projectiles we see in the comic don't impact violent enough to be flying at relativistic speeds. There's explosions, but not nuke-like flashes that rip half the station apart in an instant.

I would therefore assume that these railguns don't shoot at relativistic speeds at all. At least not at their current power level. Don't wanna rule out that one can tune them up for long range shots ;)

From the impact effects I would assume these are flying at a few tens of kilometers per second - several times orbital speed - at most, but not at any significant fraction of light speed.

If they were, there'd have been more of a light show and less of a spacestation.

LeonT
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Re: Official "Discuss the latest page" thread

Post by LeonT » Mon Oct 15, 2018 11:06 pm

CorvusCorax wrote:
Mon Oct 15, 2018 2:54 pm
Physically modelling impacts at these velocities ( even just orbital speed impacts, but this also goes for relativistic speeds ) is done by considering both the projectile and the impacted material as a fluid.
The kinetic energies in the area of impact are much higher than the bond energies betwern molecules ( at relativistic speeds even between atoms, possibly even between subatomic particles, after all you are hitting at speeds comparable to those in a particle accelerator )

As such you can model the impact of a railgun bullet on armor / atmosphere as the intersection of a hypercritical fluid streams, or even proton/gluon plasma of varying densities. At these energy levels everything is a fluid.

As the projectile hits, it would not so much penetrate, but fuse with the material it hits in a nonelastic matter, where any material involved is itself accelerated. Like a shock wave.

Like in a tank hit by a shell, most of the damage inside a ship would not be done by particles from the original projectile - at relativistic spees impacts, those would likely have converted to hard radiation at that point - but by matter accelerated by thus shockwave.

Even thick spaceship armor is way too thin for this shockwave to dissipate. You woild simply have matter, lets say 10 times the mass of the original projectile, flying through the interior at 1/10 th the speed. ( which is still tenth of thousands of kilometers per second! ) impacting interior walls and the hull on the other side and creating secondary shockwaves.

It would act like a dum dum bullet. Tiny impact hole, large part of the ship ripped out on the opposite side.


Atmosphere is a different matter. It has only a tiny fraction of the density, but, as before, one has to model the impact as individual impacts vetween particles. Unlike ship armor, the atmosphere is kilometers thick and gets thicker further in/down. This transfers all the energy into a plasma shockwave very quickly which then spreads out over a very large area. It doesm't matter that the atmosphere is lower density than the projectile, since at hypersonic speeds, a shockwave forms in front of the projectile in which the pressure increases until it matches up in density - and beyond.

This shockwave wouldn't be harmless of course. The effect would be comparable to a nuclear bomb, ignited in the high atmosphere, complete with radiation and EMP effects and shattered windows in hundreds of kilometers around the entry trajectory. Not much fallout though, luckily there's not enough mass in the projectile.

A good first order aproximation of a relativistic speed impact can be made by stripping a small nuclear bomb with the same yield as the impactors kinetic energy to the hull and igniting it. Only difference is, the impactor acts more like a nuclear shaped charge, with most of the damage on the opposing side of the ship. ;) You'd also get a similar radiation release.

Firing that at a space station with civilians in it...

"war crime" kinda sums it up ;)
Thanks for the science :-)

CygnusX1
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Re: Official "Discuss the latest page" thread

Post by CygnusX1 » Tue Oct 16, 2018 4:20 am

Woohoo! Quite a lot of hard-SF info here, thank you for the interesting read!

I imagine that if you own a gun shooting things at relativistic speeds you don't mind fighting at huge distances. E.g. Earth-to-Moon? That's less than a light-second away...

Crimson Dark is not going for that hard-SF though. For example, I think the average combat distances are actually smaller than 50km. In most fights you are able to see your opponent, fly next to them. The Behemoth is probably the only case of combat fought at slightly greater distance - but even then it or its target are bigger than just a tiny dot in the sky.

It is also established in the CD universe that rotating your ship is not an easy task. Remember this fight for example? Larissa comment suggest that most ships, including Niobe, can't do just that.
Similarly, here the destroyer cannot just rotate in seconds and resume firing...

While neither of the above cases were about rolling, it may still be hard or impossible for Strix to keep small profile against the fast-moving target it is fighting with. Especially, if the said target is rolling too.

CygnusX1
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Re: Official "Discuss the latest page" thread

Post by CygnusX1 » Tue Oct 16, 2018 4:28 am

Regarding the Kessler syndrome, if the debris is moving in random direction and random speeds, won't we get something resembling a debris ring or debris sphere, rather than a concentrated group of objects hitting the origin point every 2 hours or so?

Aegeus
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Re: Official "Discuss the latest page" thread

Post by Aegeus » Tue Oct 16, 2018 6:29 am

I doubt Kessler syndrome is much of an issue in this setting. Tiny bits of debris are a disaster in real life because real rockets are made of tinfoil and paper mache and even a small impact will tear them apart, but this is a soft sci-fi setting where the ships have actual armor (and the big beefy engines needed to push all that armor around without breaking a sweat). Even the merchant ships are tough enough to take a few hits.

Yes, it's true that a piece of debris moving at orbital velocity is going to hit you like a speeding bullet, but the Wraith is currently flying through a hail of actual bullets and surviving.

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