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Post by tepidbread on Sept 26, 2018 0:43:59 GMT
So I have never really explored building large bore/mass railguns so I thought I would give it a try. I build a railgun capable of shooting a 1kg projectile at 10km/s. I quickly noticed that it was really under preforming when I tested it against the "silo ship" default craft. Given that it is like 50MJ I would expect it to smash through whipple shields and the subsequent layers of armor with ease and smash whatever is inside. However, it seemed to just disappear with almost no noticeable damage. I am skeptical that this would be the case in real life. Is this a failing of the damage model? ![]() Attachments:
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Post by Pttg on Sept 28, 2018 17:29:45 GMT
I think I've seen the same problem in my designs. Looks like your design should be sufficient to duplicate the problem.
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Post by Rocket Witch on Sept 28, 2018 18:10:36 GMT
As I recall, user omnipotentvoid noted this in a fairly extensive thread in the support forum, so this should be a known issue, but there isn't a public list of these for us to tell.
It's also possible for a sufficiently massive shot to overpenetrate and appear to do no damage if you have bloom turned down/off, though in such cases there should be black armour tiles on the overlay for the enemy ship.
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Post by AtomHeartDragon on Sept 28, 2018 19:31:04 GMT
so it's approximately a 2cm thick circular plate of osmium.
How does it fare against de-whippled target or at lower velocities? Also, does it ricochet, overpenetrate or is absorbed?
Can anyone here calculate how much of those 50MJ (11.11 Ricks) are going to be absorbed by the osmium slug as it hits corresponding 5mm circular plate of aluminium?
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Post by tepidbread on Sept 29, 2018 16:29:14 GMT
I haven't really done much testing with it. I can do some more later this weekend. It seemed to just disappear after hitting the target. No visible tracer exiting the other side. I don't know if it was removing the armor in the spots it was hitting because I did not look at the armor overlay. I have not tried it against a non-Whipple shielded target, however it should pass through Whipple shields fairly easily given the mass and dimensions of the projectile. (Not to mention osmium's great mechanical properties) I will also export the weapon rather than a just a screenshot.
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Post by AtomHeartDragon on Sept 29, 2018 19:16:42 GMT
Assuming perfectly inelastic collision your 1kg osmium slug punches through ship's aluminium whipple shielding taking a 106g aluminium plate along for a ride.
In the process it loses about 5.6MJ of energy that is used to heat up both it and the chunk of aluminium it appropriated (as it has nowhere else to go; we are ignoring the fact that the impact has most likely thoroughly pulverized your osmium slug as at nearly 11km/s there is no longer such thing as mechanical properties, since it probably doesn't have time to matter) - that might be not much compared to slug's total energy but it's actually quite a lot (it doesn't seem to be enough to vaporize the entire slug, but I would imagine sudden release of 5.6MJ of blam to have some effect on the remainder of the projectile and its trajectory, and given that there is not going to be enough time for osmium to transfer the heat, we can safely assume there is going to be about 5.6MJ of blam in the form violently vaporized osmium with a bit of aluminium mixed in - can anyone take over with the physics?)
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Post by anotherfirefox on Oct 7, 2018 10:54:51 GMT
Any progress?
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Post by tepidbread on Oct 7, 2018 14:09:41 GMT
Yes, but not really worth reporting. I kind of gave up on big railguns. I tried to test against single layer armor, sloped armor, and Whipple shields. It turns out that it is much easier to bounce a 1kg projectile with 50MJ of energy than I would have thought possible. Whipple shields do not do anything to stop the projectile, nor does thick monolithic armor. It just seems to go through both sides of the ship without doing much damage. Sometimes it mysteriously didn't even make a mark on the surface of the armor and the projectile disappeared. Sometimes a tracer could be seen exiting the far side of the ship whilst leaving no visible damage. Sometimes small holes appeared in the armor. I decided to use flak projectiles and that is when the gun started doing noticeable damage (The flak was focused into a tight cone and would bore huge holes into the enemy ship). So I gave up and made a 10km/s flak missile.
I am apprehensive at best that a projectile of any material would act in the way that the game portrays in such a high energy collision. I do not think that the current damage model can handle such collisions.
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Post by anotherfirefox on Oct 7, 2018 14:37:36 GMT
Yes, but not really worth reporting. I kind of gave up on big railguns. I tried to test against single layer armor, sloped armor, and Whipple shields. It turns out that it is much easier to bounce a 1kg projectile with 50MJ of energy than I would have thought possible. Whipple shields do not do anything to stop the projectile, nor does thick monolithic armor. It just seems to go through both sides of the ship without doing much damage. Sometimes it mysteriously didn't even make a mark on the surface of the armor and the projectile disappeared. Sometimes a tracer could be seen exiting the far side of the ship whilst leaving no visible damage. Sometimes small holes appeared in the armor. I decided to use flak projectiles and that is when the gun started doing noticeable damage (The flak was focused into a tight cone and would bore huge holes into the enemy ship). So I gave up and made a 10km/s flak missile.
I am apprehensive at best that a projectile of any material would act in the way that the game portrays in such a high energy collision. I do not think that the current damage model can handle such collisions.
that explains something... Thanks |
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Post by AtomHeartDragon on Oct 7, 2018 15:09:25 GMT
Not saying that the damage model works just fine or that it isn't some stupid issue like actual collision squeezing by between two frames of simulation, but a few things to consider:
- Hypervelocity impacts essentially resemble an incredibly tiny nuke going off against the armour - material, both projectile and armour, is vaporized, turned into plasma and violently ejected. Small projectiles vaporize completely, large ones receive hard kick from their own vaporized ejecta and likely shatter. This hard kick might also deflect them on oblique impacts.
- As with nukes, all sorts of explosions work very counter-intuitively in vacuum - you pretty much get no blast, as blast is what happens when you deliver explosion's energy to a large mass of inert atmosphere - temperature drops but you get a shockwave carrying a lot of momentum and breaking things. In vacuum you get just bright, hot flash and a faint waft of hot plasma. At best you count on some spallation from the periphery of the crater carrying extra momentum and wreaking corresponding amounts of extra havoc.
- At low velocities projectile's shape and mechanical properties are important, as you go faster only cross-sectional density matters (Newtonian approximation) and long rods become optimal penetrators, as you go even faster it stops being your projectile that penetrates anything but you start blasting craters like with pulsed laser - at this point I expect long rods to become vastly suboptimal as they simply mean that more of your projectile is further away from the armour as it is being pulverized by the explosion - coinguns bringing as much of the projectile's mass as possible in contact with the armour simultaneously should perform better (and unfolding linear or other shape projectiles may perform better still, but see below) and armour-piercing would probably be better achieved by launching multiple accurate projectiles in quick succession - again like with pulsed lasers where you seek to blast subsequent craters at the bottom of the last formed one after the ejecta have dispersed. This is also what could be behind the effectiveness of shotgunning the armour with hypervelocity flak.
- If anything I expect slug collisions to be better modelled than direct payload collisions - much to dismay of needlegun aficionados and as much as shooting 10m 5kg unfolding transverse rods out of 1GW railgun might be fun (tried it, it IS fun).
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Post by anotherfirefox on Oct 8, 2018 8:45:02 GMT
Not saying that the damage model works just fine or that it isn't some stupid issue like actual collision squeezing by between two frames of simulation, but a few things to consider:
- Hypervelocity impacts essentially resemble an incredibly tiny nuke going off against the armour - material, both projectile and armour, is vaporized, turned into plasma and violently ejected. Small projectiles vaporize completely, large ones receive hard kick from their own vaporized ejecta and likely shatter. This hard kick might also deflect them on oblique impacts.
- As with nukes, all sorts of explosions work very counter-intuitively in vacuum - you pretty much get no blast, as blast is what happens when you deliver explosion's energy to a large mass of inert atmosphere - temperature drops but you get a shockwave carrying a lot of momentum and breaking things. In vacuum you get just bright, hot flash and a faint waft of hot plasma. At best you count on some spallation from the periphery of the crater carrying extra momentum and wreaking corresponding amounts of extra havoc.
- At low velocities projectile's shape and mechanical properties are important, as you go faster only cross-sectional density matters (Newtonian approximation) and long rods become optimal penetrators, as you go even faster it stops being your projectile that penetrates anything but you start blasting craters like with pulsed laser - at this point I expect long rods to become vastly suboptimal as they simply mean that more of your projectile is further away from the armour as it is being pulverized by the explosion - coinguns bringing as much of the projectile's mass as possible in contact with the armour simultaneously should perform better (and unfolding linear or other shape projectiles may perform better still, but see below) and armour-piercing would probably be better achieved by launching multiple accurate projectiles in quick succession - again like with pulsed lasers where you seek to blast subsequent craters at the bottom of the last formed one after the ejecta have dispersed. This is also what could be behind the effectiveness of shotgunning the armour with hypervelocity flak.
- If anything I expect slug collisions to be better modelled than direct payload collisions - much to dismay of needlegun aficionados and as much as shooting 10m 5kg unfolding transverse rods out of 1GW railgun might be fun (tried it, it IS fun).
So is it aspect ratio? I did a super short experiment with same velocity same matter penetrator, one with common armature with 5.3mm bore radius and 25g mass, one with 10cm long needle with 0.15g mass. The needle did way far better. |
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Post by AtomHeartDragon on Oct 8, 2018 9:22:24 GMT
The problem with payload needles is that I wouldn't vouch for their correctness (granted, I wouldn't vouch for slug physics correctness either, but that's on another level) - I have seen too many spaceship collisions going all wonky in game and payload is essentially a tiny spaceship from engine's POV. I have also seen and did hilarious, but not sure if entirely physical things using radiators on payloads to blow gapping holes in ships. Slug needless, OTOH are notoriously hard to get to work with RGs and chemguns, although you could try with coilguns as they seem well suited for long, narrow projectiles: Make a low bore coilgun and high bore railgun firing slugs of same mass and comparable material at the same velocity and rate of fire, adjust accuracy by applying enough graphogel and compare performance in the same conditions.
Also test over a range of impact velocities as I expect needless to start falling behind at some point (where you cross from "two liquids with one poking hole in another" to "blasting nice circular craters in stuff, also plasma"): (3.17mm aluminium sphere hitting emptied air cylinder at 7.03km/s in vacuum)
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