Meteor vs. Projectile

[Jake]

I have an aerospace related question. A meteor, as outlined here: http://aquarid.physics.uwo.ca/~pbrown/E ... 201997.pdf, produces a variety of visual effects, including brightness great enough to cause shadows on a sunny day and turning the landscape red. It travels at 25 km/sec upon entering the atmosphere. The meteor’s original mass is 15 tons. With the density of rock at around 2.7ton/m^3, we get a volume of 5.56m^3. Now, imagine that a projectile made from an unknown alloy of tungsten, iron, and possibly carbon has 12.5X the volume of the meteor (69.52m^3), is moving 5.24X as fast (131km/sec), and has 40X the mass (600 ton). It travels for 1 second before impacting a very tall, impenetrable structure 7km off the ground. Will it produce visual affects that are similar to the meteor, more pronounced than the meteor, or less pronounced? Also, assume the projectile is as aerodynamic as we can make it.

[Norade]

That has to be the worst wording on a post I have seen for a while. Anyway, this is needed for a debate about Halo firepower so the objects in question are a random space rock entering the atmosphere versus a MAC round.

The Asteroid has the following properties:
Mass: 15tons - Density: 2.7kg/m3 - Volume: ~5.56m3 - Radius: ~1.01m - Surface Area: ~12.8m3 Velocity: 25km/s

The MAC Round using the density of High Speed Steel:
Mass: 600tons - Density: 10.17kg/m3 - Volume: ~59m3 Radius: ~0.75m Length: ~34m - Surface Area: 163.8m3 Velocity: 131km/s

The MAC Round using the density of Tungsten Carbide:
Mass: 600tons - Density: 15.8kg/m3 - Volume: ~38m3 Radius: ~0.65m Length: ~30m - Surface Area: ~125.2m3 Velocity: 131km/s

Note that the lengths and diameters for the MAC rounds are taken from rough approximations of a current penetrator rounds with follow a roughly 1:20 width to length ratio.

[Feil]

Figures use the smaller projectile.

Your projectile will radiate at roughly 7.5E13 Watts using the drag equation, provided cross-sectional area and velocity, and assuming a drag coefficient of 0.04 for 'as aerodynamic as we can make it', ignoring the heat capacity and initial temperature of the projectile.

Assuming a cylindrical blackbody for ease of estimation, and applying the stephan-boltzmann equation, yields a temperature of some 6.34E4 Kelvins. That's roughly ten times the temperature of the surface of the sun.

Further applying the Planck Radiation Law, I hope you brought some sunscreen, because that motherfucker is kicking most of its energy in the ultraviolet and glowing brighter than the noonday sun. If you are stupid enough to look at it, it will be violet-white in hue. And then it will hit its target. And then you will be blind anyway, as it dumps more energy than an atom bomb into its target.

Then, depending on your distance and orientation from the point of impact, you will either go deaf first from the sonic booms rolling over you , THEN die in the blast wave, or die in the blast wave before you hear a sound. For most people killed by the weapon, it will be entirely silent, which is pretty cool in a horrific, macabre kind of way.

Why in the name of Christ do you need a 600 tonne projectile traveling at 131km/s? That's a little skyward of a gigatonne TNT if my mental arithmetic is right....

[darthdavid]

Why in the name of Christ do you need a 600 tonne projectile traveling at 131km/s? That's a little skyward of a gigatonne TNT if my mental arithmetic is right....

Well some things take a lot of killing I guess...

[Feil]

6.34E5K, not E4. Typo.

[Norade]

First off, thanks for help with that Feil. I can do most basic physics, but I never took anything beyond grade 11 in high school so doing this myself was pretty well beyond me. It also looks as if I may have overestimated the effects of being aerodynamic.

Anyway, a few more questions if you're inclined to answer them.

1. How much extra energy beyond the purely kinetic should one expect the added energy from atmospheric friction to add to an observed explosion caused by the impact of such a projectile?

2. Is there anything that might be done to mitigate a shock wave caused by this? If not, which I suspect, how long would it take such a shock wave to travel back to the source of the projectile?

The last thing is that, according to the calculations done by Mike's Relativity Calculator the projectile 'only' has ~5.15 x 1015 J of energy to release on impact and that works out to ~1.2 Megatons. Of course I'm not sure how accurate that calculator is or what other factors such as energy stored due to friction may cause.

[Feil]

1: effectively none (indeed, a slight negative number, since drag is a dissipative force (spreading out the energy along the object's path, rather than delivering it all at once). However, the drag contribution is on the order of E13J, while the impact has order E15J, so the contribution is negligible in any account.

2: The effect will be very like a nuclear weapon of similar energy magnitude, with one notable exception*. For a single-digit-megaton blast, you're looking at a leveled city, but that's about it. An observer 131km away should be perfectly safe.

3: You are quite correct. I should know better than to try doing unfamiliar unit conversions in my head. A megaton impact is considerably more reasonable. Perhaps they want to blow up cities without dealing with fallout afterward.

*The exception being that momentum and pressure are far more lethal destructive tools than energy. A hardened underground structure might survive a proximity nuclear blast; it would not survive being hit by this weapon, which would punch into it even as it dumped its energy into the surrounding environment, vaporizing it, super-heating the vapor and surrounding atmosphere, and causing, thereby, an explosive shockwave.

By the way, aerodynamic shape is important. If the projectile were a blunt-nosed cylinder shape like a bullet, rather than a streamlined teardrop shape, its radiant flux would be about an order of magnitude higher.

[Norade]

1: effectively none (indeed, a slight negative number, since drag is a dissipative force (spreading out the energy along the object's path, rather than delivering it all at once). However, the drag contribution is on the order of E13J, while the impact has order E15J, so the contribution is negligible in any account.

D'oh, I should have realized that, conservation of energy and all...

2: The effect will be very like a nuclear weapon of similar energy magnitude, with one notable exception*. For a single-digit-megaton blast, you're looking at a leveled city, but that's about it. An observer 131km away should be perfectly safe.

*The exception being that momentum and pressure are far more lethal destructive tools than energy. A hardened underground structure might survive a proximity nuclear blast; it would not survive being hit by this weapon, which would punch into it even as it dumped its energy into the surrounding environment, vaporizing it, super-heating the vapor and surrounding atmosphere, and causing, thereby, an explosive shockwave.

Oh, that actually means the scene in question totally makes sense. I thought that their might be a large visible shockwave, but from so far away it could be pretty tough to spot. That's really good to know in terms of the debate.

3: You are quite correct. I should know better than to try doing unfamiliar unit conversions in my head. A megaton impact is considerably more reasonable. Perhaps they want to blow up cities without dealing with fallout afterward.

In this case they were shooting at another vessel in atmosphere and I'm using the data to provide a bracket for firepower and disprove the book statement that Halo verse is tossing around 600 tonne rounds at 40% the speed of light. After all if three hits at that power are needed to kill a ship then you wouldn't even bother firing shots many, many, orders of magnitude weaker.

By the way, aerodynamic shape is important. If the projectile were a blunt-nosed cylinder shape like a bullet, rather than a streamlined teardrop shape, its radiant flux would be about an order of magnitude higher.

Oh, I knew it was important, but I was thinking that it could do even more to mitigate the effects. That said given the energies being tossed around a streamlined shape does make a huge difference.

[Jake]

By the way, aerodynamic shape is important. If the projectile were a blunt-nosed cylinder shape like a bullet, rather than a streamlined teardrop shape, its radiant flux would be about an order of magnitude higher.

If it was bullet like (the round is supposed to be armor piercing), how bright would it glow? Also, looking at this scene: http://www.youtube.com/watch?v=vj6SFdPaE_s from 0:30 to 0:40, would the effects shown in the scene match up with the characteristics you described (they show the ships firing, pretty much ground zero, and it doesn't look like a violet white light brighter than the noon sun to me...)?

[Norade]

By the way, aerodynamic shape is important. If the projectile were a blunt-nosed cylinder shape like a bullet, rather than a streamlined teardrop shape, its radiant flux would be about an order of magnitude higher.

If it was bullet like (the round is supposed to be armor piercing), how bright would it glow? Also, looking at this scene: http://www.youtube.com/watch?v=vj6SFdPaE_s from 0:30 to 0:40, would the effects shown in the scene match up with the characteristics you described (they show the ships firing, pretty much ground zero, and it doesn't look like a violet white light brighter than the noon sun to me...)?

Armor piercing isn't bullet shaped you dishonest goat fucking donkey rapist.





Notice the slight difference in shapes?

[Sea Skimmer]

Notice the slight difference in shapes?

Actually you fucking idiot, armor piercing ammunition can and often is blunt as fuck, just look at the actual shape of any heavy armor piercing naval shell without the windscreen. Even sabot rounds actually are flat on the nose, not pointed because the point would just break off. Furthermore most armor piercing small arms ammunition is some kind of composite round with the hard core buried inside a softer material, so just looking at the bullet doesn’t tell you anything. Two fucking pictures do not make an argument on such a wide-ranging topic as to what constitutes armor piercing ammunition and the constraints placed by weapon design on ammunition design.

[Feil]

If it was bullet like (the round is supposed to be armor piercing), how bright would it glow? Also, looking at this scene: http://www.youtube.com/watch?v=vj6SFdPaE_s from 0:30 to 0:40, would the effects shown in the scene match up with the characteristics you described (they show the ships firing, pretty much ground zero, and it doesn't look like a violet white light brighter than the noon sun to me...)?

http://en.wikipedia.org/wiki/Drag_equation
http://en.wikipedia.org/wiki/Drag_coefficient
Power = Force*Velocity
http://en.wikipedia.org/wiki/Stefan%E2% ... tzmann_law

Following the links in order should provide you with all the information you need for whatever permutations to the problem you wish to consider. None of the math is more complex than basic algebra.

[Norade]

Notice the slight difference in shapes?

Actually you fucking idiot, armor piercing ammunition can and often is blunt as fuck, just look at the actual shape of any heavy armor piercing naval shell without the windscreen. Even sabot rounds actually are flat on the nose, not pointed because the point would just break off. Furthermore most armor piercing small arms ammunition is some kind of composite round with the hard core buried inside a softer material, so just looking at the bullet doesn’t tell you anything. Two fucking pictures do not make an argument on such a wide-ranging topic as to what constitutes armor piercing ammunition and the constraints placed by weapon design on ammunition design.

Hmm, so an APFSDS round that is long, thing, with a pointed tip isn't an armor piercing round now? Not to mention that capped shells as well as penetrators buried within larger softer shells fell out of favor due to worse ballistics after the advent of the APDS round and later the APFSDS round. While there has been a slight shift back to slightly stubbier rounds due to fears that new armors may be able to sheer off the tips of these rounds to my knowledge this is still merely speculation and generally speaking an APFSDS round is considered the best kinetic penetrator available today.

Not to mention that a Halo MAC gun, the weapon being discussed here damn near certainly fires a ferric tungsten or DU round which almost certainly is not going to be shaped the same as a modern handgun, rifle, or machine gun bullet. Also you would not refer to a round fried from a tanks main weapon or a ship's cannon a bullet in common speech. Of further note is the fact that modern naval railgun shells follow the same shape as the shape I have suggested for a MAC guns round.

So kindly fuck off Skimmer, your point that not all armor penetrating rounds follow the guidelines for an APFSDS round don't apply here.

[Sea Skimmer]

Hmm, so an APFSDS round that is long, thing, with a pointed tip isn't an armor piercing round now?

Did you know the first use of sabot was in fact for longer range with high explosive shells? This was more common then armor piercing use in WW2.

Not to mention that capped shells as well as penetrators buried within larger softer shells fell out of favor due to worse ballistics after the advent of the APDS round and later the APFSDS round.

APDS was almost worthless because it was so erratic. Capped shells died out mainly because battleships which had to be attacked with exploding armor piercing ammunition died out.

While there has been a slight shift back to slightly stubbier rounds due to fears that new armors may be able to sheer off the tips of these rounds to my knowledge this is still merely speculation and generally speaking an APFSDS round is considered the best kinetic penetrator available today.

Best penetration sure, at speeds at which the projectile can survive intact, but also the worst behind armor effects which make it unsuited to large targets like say a large spaceship. You could shoot sabot at a battleship all day, put holes through both sides, and you wouldn’t accomplish much until you had hundreds of hits. This is why you know we have bunker busters and crap, even ones made out of DU, which have explosive payloads to blow the target the fuck up. Sabot makes sense against tanks because tanks are tiny and putting a round hole in them is still likely to knock the tank out, though plenty of tanks are repairable afterwards because of the limited damage.

Not to mention that a Halo MAC gun, the weapon being discussed here damn near certainly fires a ferric tungsten or DU round which almost certainly is not going to be shaped the same as a modern handgun, rifle, or machine gun bullet.

Considering it’s a fucking space weapon the tip shape doesn’t damn well matter very much, and blunt ends have more mechanical strength which is going to be damn important if the speed is to be any higher then that achieved by modern tank cannon.

Also you would not refer to a round fried from a tanks main weapon or a ship's cannon a bullet in common speech. Of further note is the fact that modern naval railgun shells follow the same shape as the shape I have suggested for a MAC guns round.

They also fly in the atmosphere.

So kindly fuck off Skimmer, your point that not all armor penetrating rounds follow the guidelines for an APFSDS round don't apply here.

You can be an idiot all you want, you do the job well, but its just hilarious how you not once even consider the fact that a space weapon suffers from no drag, and so the normal rules that apply to nose shaping for earth based weapons don’t apply either.

The only consideration for projectile design would be the impact with the target and for that a very sharp point wont fucking matter at 131km/s. In fact the performance of the projectile is going to be about identical if it was completely flat or infinitely pointy because it’s just going to vaporize on impact. Since a blunt end is cheaper to produce, less likely to be damaged in storage and most importantly, more compact allowing the user to store more ammunition on the ship it’s not unlikely to be used. Even if you wanted to bombard from orbit, it still wont matter since a 600 ton object at 131km/s is going to create a massive air burst either way.

[Norade]

Hmm, so an APFSDS round that is long, thing, with a pointed tip isn't an armor piercing round now?

Did you know the first use of sabot was in fact for longer range with high explosive shells? This was more common then armor piercing use in WW2.

Yes, for broad strokes I did know that sabots were used to increase range and velocity for sub caliber rounds. The term comes from a french word for clogs as the first sabots were made of wood. I was less aware of its use in WWII, but I did know that such rounds existed.

Not to mention that capped shells as well as penetrators buried within larger softer shells fell out of favor due to worse ballistics after the advent of the APDS round and later the APFSDS round.

APDS was almost worthless because it was so erratic. Capped shells died out mainly because battleships which had to be attacked with exploding armor piercing ammunition died out.

My, admittedly limited, sources also suggest that the superior ballistics of a longer slimmer round played a factor in the demise of the capped shell. I also have no idea where shell designs for ship to ship ballistic combat would have gone if air power and missiles hadn't come along.

While there has been a slight shift back to slightly stubbier rounds due to fears that new armors may be able to sheer off the tips of these rounds to my knowledge this is still merely speculation and generally speaking an APFSDS round is considered the best kinetic penetrator available today.

Best penetration sure, at speeds at which the projectile can survive intact, but also the worst behind armor effects which make it unsuited to large targets like say a large spaceship. You could shoot sabot at a battleship all day, put holes through both sides, and you wouldn’t accomplish much until you had hundreds of hits. This is why you know we have bunker busters and crap, even ones made out of DU, which have explosive payloads to blow the target the fuck up. Sabot makes sense against tanks because tanks are tiny and putting a round hole in them is still likely to knock the tank out, though plenty of tanks are repairable afterwards because of the limited damage.

I'm not actually sure what a 600 ton ferric tungsten or DU round could survive though I am willing to admit at the speeds a MAC gun is supposed to fire they would likely not survive. That said the rounds are referred to as slugs so they are likely pure kinetic impactors with no secondary effects beyond those we expect from the DU version of said rounds. If it were another sort of round and not explicitly named as a slug I would agree with you.

Not to mention that a Halo MAC gun, the weapon being discussed here damn near certainly fires a ferric tungsten or DU round which almost certainly is not going to be shaped the same as a modern handgun, rifle, or machine gun bullet.

Considering it’s a fucking space weapon the tip shape doesn’t damn well matter very much, and blunt ends have more mechanical strength which is going to be damn important if the speed is to be any higher then that achieved by modern tank cannon.

You have a point, though there is no reason to assume that they have only a single type of round. Also, the scene we observe doesn't have many visible atmospheric effects thus leading us towards the theory of the aerodynamic round as at least one type of round designed for this weapon.

Also you would not refer to a round fried from a tanks main weapon or a ship's cannon a bullet in common speech. Of further note is the fact that modern naval railgun shells follow the same shape as the shape I have suggested for a MAC guns round.

They also fly in the atmosphere.

Yes, as do MAC rounds in at least a single observed case.

So kindly fuck off Skimmer, your point that not all armor penetrating rounds follow the guidelines for an APFSDS round don't apply here.

You can be an idiot all you want, you do the job well, but its just hilarious how you not once even consider the fact that a space weapon suffers from no drag, and so the normal rules that apply to nose shaping for earth based weapons don’t apply either.

I find it funny that you think I don't know there is a lack of drag in space. However even with no drag in space that doesn't prevent the development of more than one shape of round for use against different targets.

The only consideration for projectile design would be the impact with the target and for that a very sharp point wont fucking matter at 131km/s. In fact the performance of the projectile is going to be about identical if it was completely flat or infinitely pointy because it’s just going to vaporize on impact. Since a blunt end is cheaper to produce, less likely to be damaged in storage and most importantly, more compact allowing the user to store more ammunition on the ship it’s not unlikely to be used. Even if you wanted to bombard from orbit, it still wont matter since a 600 ton object at 131km/s is going to create a massive air burst either way.

Not entirely true, as we see in the scene Jake linked to the round travels ~65.5km through atmosphere and survives to detonate against a target. The atmosphere is thicker than the distance travelled by this round, but much of that is far less dense than the air we see the round traveling through without turning into a massive fireball. We also see extremely minimal atmospheric effects from these rounds leading me to believe that they must be extremely aerodynamic.

[Sea Skimmer]

Yes, for broad strokes I did know that sabots were used to increase range and velocity for sub caliber rounds. The term comes from a french word for clogs as the first sabots were made of wood. I was less aware of its use in WWII, but I did know that such rounds existed.

Not just in WW2, the US Navy test fired a 13in subcaliber bomblet shell for its 16in guns during the late 1980s and planned an 11in version had the Cold War not ended so suddenly.

My, admittedly limited, sources also suggest that the superior ballistics of a longer slimmer round played a factor in the demise of the capped shell. I also have no idea where shell designs for ship to ship ballistic combat would have gone if air power and missiles hadn't come along.

Ballistics was important for tanks guns, for a heavy naval gun you would run into serious trouble making a smaller diameter shell which still had a useful HE payload and enough thickness and strength to pierce armor in a condition fit to burst. The loss of accuracy was also more serious, which is why that 11in concept was going to be the first GPS guided shell.

I'm not actually sure what a 600 ton ferric tungsten or DU round could survive though I am willing to admit at the speeds a MAC gun is supposed to fire they would likely not survive. That said the rounds are referred to as slugs so they are likely pure kinetic impactors with no secondary effects beyond those we expect from the DU version of said rounds. If it were another sort of round and not explicitly named as a slug I would agree with you.

Your talking about a speed of mach 467 at 100,000 meters, and mach 438 at 10,000 meters, assuming no prior slowdown. Nothing remotely real is going to survive anything close too that. It makes typical asteroid speeds look like a joke let alone anything man has built.

You have a point, though there is no reason to assume that they have only a single type of round. Also, the scene we observe doesn't have many visible atmospheric effects thus leading us towards the theory of the aerodynamic round as at least one type of round designed for this weapon.

Yeah maybe, a projectile which is also way slower then 131km/s.

Yes, as do MAC rounds in at least a single observed case.

Yes a case which does not look like the expected effects of a 10% light speed weapon weighing as much as a diesel submarine. So whatever was being fired wasn't that.

I find it funny that you think I don't know there is a lack of drag in space. However even with no drag in space that doesn't prevent the development of more than one shape of round for use against different targets.

With such dumbshit comments as 'armor piercing isn't bullet shaped' what else should I conclude about you? You act angry as fuck calling someone a rapist liar and that's your fucking argument to prove it? Its fucking wrong, and what you really know, which you didn't bother to try to share, doesn't change that it was a stupid as fuck thing to say. Armor piercing is a property ammunition may have. It is not a shape or a material or even a specific weapons design concept. Your pictures, all you offered as support, don't even remotely support your position either because that pistol bullet damn well could be AP and you could not tell by looking. That's because ammunition design is determined by more then just the desired properties. A designer may want more of a point, but his ammo has to fit the existing pistol action. You sure don't see many flechet pistols, and even if you could make the sabot technology work that small it would still suck because it would require a very long action in the pistol relative to its total firepower. No one wants a pistol in which the slide moves three inches.

Not entirely true, as we see in the scene Jake linked to the round travels ~65.5km through atmosphere and survives to detonate against a target. The atmosphere is thicker than the distance travelled by this round, but much of that is far less dense than the air we see the round traveling through without turning into a massive fireball. We also see extremely minimal atmospheric effects from these rounds leading me to believe that they must be extremely aerodynamic.

No what that means is what was fired is smaller then 600 tons of DU, and fired slower then 131km/s inital velocity. Accepting your number of 65.5km, if the round was fired at full speed and weight that would mean somehow the projectile bled off 50% of its velocity, and colossal hundreds of gigatons load of heat has to dump into the the air. Aerodynamics are irrelevant to that, if it was fired like that the energy has to go somewhere, and even if the material of the shell had an absurdly high heat tolerance it simply cannot absorb it all. In fact since the better the aerodynamics, the more heat should go into the air, the less into the projectile, which means that the lack of a huge blast as it came down is all the more evidence its not so powerful.

So best guess is they fired some kind of subcaliber sub velocity round, maybe meant for support of ground troops or even training. What its shape is remains open to argument, and may be a lot more complicated then a single curve or point too. Blunt isn't out of the question, certainly I would not expect such a construction to be highly pointy. The point would just melt off and that would risk sending the projectile out of control, tumbling at that speed wont be healthy. A sacrificial aerospike is plausible though, but the top of an aerospike is flat. The whole idea is the flatness deflects the inital bow shockwave away from the sides of the projectile. Some missiles and nuclear RVs use this setup.

[Norade]

Yes, for broad strokes I did know that sabots were used to increase range and velocity for sub caliber rounds. The term comes from a french word for clogs as the first sabots were made of wood. I was less aware of its use in WWII, but I did know that such rounds existed.

Not just in WW2, the US Navy test fired a 13in subcaliber bomblet shell for its 16in guns during the late 1980s and planned an 11in version had the Cold War not ended so suddenly.

Not an area I've studied very much, but perhaps one worth looking into.

My, admittedly limited, sources also suggest that the superior ballistics of a longer slimmer round played a factor in the demise of the capped shell. I also have no idea where shell designs for ship to ship ballistic combat would have gone if air power and missiles hadn't come along.

Ballistics was important for tanks guns, for a heavy naval gun you would run into serious trouble making a smaller diameter shell which still had a useful HE payload and enough thickness and strength to pierce armor in a condition fit to burst. The loss of accuracy was also more serious, which is why that 11in concept was going to be the first GPS guided shell.

What about the railguns being developed today? They, to my knowledge, fire solid slugs at high velocity and should fare rather well against another ship. Of course, I might be wrong there as I've only done the slightest research into the are thus far.

I'm not actually sure what a 600 ton ferric tungsten or DU round could survive though I am willing to admit at the speeds a MAC gun is supposed to fire they would likely not survive. That said the rounds are referred to as slugs so they are likely pure kinetic impactors with no secondary effects beyond those we expect from the DU version of said rounds. If it were another sort of round and not explicitly named as a slug I would agree with you.

Your talking about a speed of mach 467 at 100,000 meters, and mach 438 at 10,000 meters, assuming no prior slowdown. Nothing remotely real is going to survive anything close too that. It makes typical asteroid speeds look like a joke let alone anything man has built.

Yet, the scene in question shows what, in the absence of other know weapons, just that and has other effects that would be very close to how, to my knowledge, such an impact would look. How do we justify that?

You have a point, though there is no reason to assume that they have only a single type of round. Also, the scene we observe doesn't have many visible atmospheric effects thus leading us towards the theory of the aerodynamic round as at least one type of round designed for this weapon.

Yeah maybe, a projectile which is also way slower then 131km/s.

No, in the scene in question we know the crater is roughly 131km in diameter and that a rough estimate has the round crossing half of that distance in half a second giving us our velocity. We know the mass and a rough composition for the rounds and the fireballs we see fit some of the parameters for what we would expect an energy release on the scale to show.

Yes, as do MAC rounds in at least a single observed case.

Yes a case which does not look like the expected effects of a 10% light speed weapon weighing as much as a diesel submarine. So whatever was being fired wasn't that.

It fires from point that we know houses the MAC gun, and they have no reason to hold anything back, so what do you think they were firing?

I find it funny that you think I don't know there is a lack of drag in space. However even with no drag in space that doesn't prevent the development of more than one shape of round for use against different targets.

With such dumbshit comments as 'armor piercing isn't bullet shaped' what else should I conclude about you? You act angry as fuck calling someone a rapist liar and that's your fucking argument to prove it? Its fucking wrong, and what you really know, which you didn't bother to try to share, doesn't change that it was a stupid as fuck thing to say. Armor piercing is a property ammunition may have. It is not a shape or a material or even a specific weapons design concept. Your pictures, all you offered as support, don't even remotely support your position either because that pistol bullet damn well could be AP and you could not tell by looking. That's because ammunition design is determined by more then just the desired properties. A designer may want more of a point, but his ammo has to fit the existing pistol action. You sure don't see many flechet pistols, and even if you could make the sabot technology work that small it would still suck because it would require a very long action in the pistol relative to its total firepower. No one wants a pistol in which the slide moves three inches.

First off, an armor piercing round optimized to reduce air friction would be long and thin just as current kinetic penetrators are. We have one good scene in question to work from and in it we don't see massive shock waves from this round as it passes through the air so we know that it can't be a flat ended cylinder of a round. So what else can we conclude? That they are firing some other weapon entirely from what we expect, a weapon mentioned in no other source, or do we assume that they somehow managed to solve other problems so their main weapon works in atmosphere?

As for me being mad, I'm really not, but I don't pass up the chance to let loose and have fun with creative insults. I would also not assume that I would have to explain that I understand that there is no drag in an airless void.

As for the pictures I showed, yeah, I fucked up there. We don't know just by looking at the bullet that it is or isn't an AP round, but we can say that compared to a sabot round it is less aerodynamic. That is the point I was getting at.

Not entirely true, as we see in the scene Jake linked to the round travels ~65.5km through atmosphere and survives to detonate against a target. The atmosphere is thicker than the distance travelled by this round, but much of that is far less dense than the air we see the round traveling through without turning into a massive fireball. We also see extremely minimal atmospheric effects from these rounds leading me to believe that they must be extremely aerodynamic.

No what that means is what was fired is smaller then 600 tons of DU, and fired slower then 131km/s inital velocity. Accepting your number of 65.5km, if the round was fired at full speed and weight that would mean somehow the projectile bled off 50% of its velocity, and colossal hundreds of gigatons load of heat has to dump into the the air. Aerodynamics are irrelevant to that, if it was fired like that the energy has to go somewhere, and even if the material of the shell had an absurdly high heat tolerance it simply cannot absorb it all. In fact since the better the aerodynamics, the more heat should go into the air, the less into the projectile, which means that the lack of a huge blast as it came down is all the more evidence its not so powerful.

So best guess is they fired some kind of subcaliber sub velocity round, maybe meant for support of ground troops or even training. What its shape is remains open to argument, and may be a lot more complicated then a single curve or point too. Blunt isn't out of the question, certainly I would not expect such a construction to be highly pointy. The point would just melt off and that would risk sending the projectile out of control, tumbling at that speed wont be healthy. A sacrificial aerospike is plausible though, but the top of an aerospike is flat. The whole idea is the flatness deflects the inital bow shockwave away from the sides of the projectile. Some missiles and nuclear RVs use this setup.

131km/s isn't my number, that would be Jake's number, I was arguing for a slower 65.5km/s though that would still be amazingly fast. As for radiating energy, Feil was kind enough to do the math on that and get an energy bleed of 7.5E13 Watts which over a half second would actually only bleed 9 kilotons of energy across a distance of 65.5km. He also worked out that the shells temperature would be a shockingly high 6.34E5 Kelvins, this means that it shouldn't have been able to reach the target intact, yet somehow it did... I have no explanation for that.

Your other suggestion is plausible, but in that case it really lowers the bar for Halo firepower. I don't care, I'm arguing against Halo being powerful and this works in my favor. After all, you don't fire shots that you don't expect to do damage and if MAC guns do fire 600 ton slugs at 40% the speed of light and it takes three of these shots to down a Covenant ship then no sane Captain would have ordered shots tens if not hundreds of thousands of times weaker to be fired. That would be like firing a machinegun at an enemy tank while your main gun is reloading but in this case you can't even hit a vision block or something and do even minor damage.

[Jake]

What we have in this scene is a shell that travels 131km/sec, a shell that should produce spectacular visual effects if not disintegrate altogether. It does not do this. We know it travels around 65.5km, it is given in the game. We know it takes less than one second, which is also given in the game. What I see here is a scene that defies the laws of physics. If we assume it is moving at 65.5km/sec or faster, we have the issues stated above and throughout this thread. If we assume it is slow enough that no visual effects are produced, we have the issue that it behaves differently that it was observed (I would be kind of freaked out if I was driving a car, and I traveled 60 miles in one hour only to be told that I was going 10mph the whole way). Either way, this scene has proven to be extremely self contradictory and in my opinion, can not be used as scientific evidence.

[Norade]

What we have in this scene is a shell that travels 131km/sec, a shell that should produce spectacular visual effects if not disintegrate altogether. It does not do this. We know it travels around 65.5km, it is given in the game. We know it takes less than one second, which is also given in the game. What I see here is a scene that defies the laws of physics. If we assume it is moving at 65.5km/sec or faster, we have the issues stated above and throughout this thread. If we assume it is slow enough that no visual effects are produced, we have the issue that it behaves differently that it was observed (I would be kind of freaked out if I was driving a car, and I traveled 60 miles in one hour only to be told that I was going 10mph the whole way). Either way, this scene has proven to be extremely self contradictory and in my opinion, can not be used as scientific evidence.

To my mind the conclusion being reached is pretty bunk, we know they fired something and can observe the effects. That's like saying we can't analyze the power of a turbolaser because we don't know how it works.

[Jake]

To my mind the conclusion being reached is pretty bunk, we know they fired something and can observe the effects. That's like saying we can't analyze the power of a turbolaser because we don't know how it works.

So are you going with the ignore the projectile's interaction with its environment and use the observed speed route or the ignore the projectile's observed speed in favor of explaining the environmental effects route? Either way, you are blatantly ignoring one part of the equation. The turbolaser is different. Everything about it is exotic. We don't know the behavior of tibanna gas, durasteel, or the hypermatter that powers it. On the other hand, we do know the behaviors of iron and tungsten and their interaction with atmosphere. Do you see where I'm going? The problem with the MAC gun is we do know a lot about how it works, and in this particular scene we see that how it works is violating important laws of physics.

[Norade]

To my mind the conclusion being reached is pretty bunk, we know they fired something and can observe the effects. That's like saying we can't analyze the power of a turbolaser because we don't know how it works.

So are you going with the ignore the projectile's interaction with its environment and use the observed speed route or the ignore the projectile's observed speed in favor of explaining the environmental effects route? Either way, you are blatantly ignoring one part of the equation. The turbolaser is different. Everything about it is exotic. We don't know the behavior of tibanna gas, durasteel, or the hypermatter that powers it. On the other hand, we do know the behaviors of iron and tungsten and their interaction with atmosphere. Do you see where I'm going? The problem with the MAC gun is we do know a lot about how it works, and in this particular scene we see that how it works is violating important laws of physics.

Just like how shields, and rings that when fired will kill all life everywhere, but not harm inorganic materials, and slip space portals that are wormholes plus don't rape physics. Besides, if we see a shot like that was just need to assume that they did something to make it all work and that all is not 100% as it seems in that scene. Somehow the UNSC has created a material that absorbs more heat that should be possible while staying solid and called it ferris tungsten. Fuck if I know how it works, but I do know that the scene exists in universe and that we can't just ignore it because it doesn't fit. That is not how analyzing sci-fi works.

[Jake]

Just like how shields, and rings that when fired will kill all life everywhere, but not harm inorganic materials, and slip space portals that are wormholes plus don't rape physics.

Your furthering my point here. The whole virtue of the shields, rings, etc is that we have no idea how they work, just like hypermatter. Until we know how they do work, we can not determine whether they violate any laws of physics or not. On the other hand, we have a very good idea how the MAC works.

Besides, if we see a shot like that was just need to assume that they did something to make it all work and that all is not 100% as it seems in that scene.

We just need to assume that the ships fired at .4c and they did something to make it all work and that all is not 100% as it seems from that scene.... yah.... how does it feel when the opposing side uses that?

Somehow the UNSC has created a material that absorbs more heat that should be possible while staying solid and called it ferris tungsten.

Somehow the UNSC has made a material that can absorb heat generated by a .4c projectile fired in atmosphere and they decide to name it after already named elements....

Fuck if I know how it works, but I do know that the scene exists in universe and that we can't just ignore it because it doesn't fit. That is not how analyzing sci-fi works.

Fuck if I know how it works, but they fire at .4c in the books and since 131km/sec doesn't have to fit, why can't we use .4c, which is at least given in the encyclopedia?

PS, you didn't answer my first question. Which part of the scene will you ignore? I'm going to bed.

[Norade]

Just like how shields, and rings that when fired will kill all life everywhere, but not harm inorganic materials, and slip space portals that are wormholes plus don't rape physics.

Your furthering my point here. The whole virtue of the shields, rings, etc is that we have no idea how they work, just like hypermatter. Until we know how they do work, we can not determine whether they violate any laws of physics or not. On the other hand, we have a very good idea how the MAC works.

Obviously we don't know how the MAC gun works if we can't figure out how the projectiles it fires don't blow up in atmosphere before impacting their target.

Besides, if we see a shot like that was just need to assume that they did something to make it all work and that all is not 100% as it seems in that scene.

We just need to assume that the ships fired at .4c and they did something to make it all work and that all is not 100% as it seems from that scene.... yah.... how does it feel when the opposing side uses that?

That tired line again, we clearly see the last shot fired about a second before we see a new fireball blossom on the keyship so we have a rough time frame of at the very lowest a tenth of a second to at highest a second.

Somehow the UNSC has created a material that absorbs more heat that should be possible while staying solid and called it ferris tungsten.

Somehow the UNSC has made a material that can absorb heat generated by a .4c projectile fired in atmosphere and they decide to name it after already named elements....

That's bullshit and you know it, but keep repeating that as if it makes it true and pretend it fits with bthe sub kiloton shots we see in Halo 2 and the asteroid collision we see later in Halo 3.

Fuck if I know how it works, but I do know that the scene exists in universe and that we can't just ignore it because it doesn't fit. That is not how analyzing sci-fi works.

Fuck if I know how it works, but they fire at .4c in the books and since 131km/sec doesn't have to fit, why can't we use .4c, which is at least given in the encyclopedia?

PS, you didn't answer my first question. Which part of the scene will you ignore? I'm going to bed.

Except that the majority of scene actually fits if the projectile masses 600 tons and is moving at roughly 131km/s. The fireball size is too large but that is a possible shield interaction, the fireball duration fits to within an order of magnitude. The only thing that we have to explain is why the round isn't glowing and why the atmosphere isn't on fire and that could be done by saying the used a laser, which could be invisible to the naked eye, to clear a channel for the shot to travel down.

No laws of physic broken, the scene still works, and the MAC gun is still a MAC gun. Unlike your assertion that the shot could be traveling at 0.4c, which it clearly isn't, I can back it up with more than if you're wrong I must be right.

[Korvan]

Except that the majority of scene actually fits if the projectile masses 600 tons and is moving at roughly 131km/s. The fireball size is too large but that is a possible shield interaction, the fireball duration fits to within an order of magnitude. The only thing that we have to explain is why the round isn't glowing and why the atmosphere isn't on fire and that could be done by saying the used a laser, which could be invisible to the naked eye, to clear a channel for the shot to travel down.

No laws of physic broken, the scene still works, and the MAC gun is still a MAC gun. Unlike your assertion that the shot could be traveling at 0.4c, which it clearly isn't, I can back it up with more than if you're wrong I must be right.

Not sure how hot you have to get air to clear a channel through it, but lightning does it by heating the air to about 30,000 degress C. Depending on how long you have the projectile taking to travel the distance, varying sizes of channels are needed. It the projectile only takes 1/10 of a sec, the channel can have a radius of 0.77 m. If it takes a full second, the channel will have to have a radius of 3.2 metres to allow for the distance the projectile drops. I did some quick calcs and found you'd need about a 44 GW laser for the 1/10 of a sec shot and about 77 GW for a full second with the larger channel.

However, I'm pretty sure this heating of the air by a laser to create a channel would be visible even if the laser is not. It likely will look pretty much like lightning does, except the stroke will be a lot straighter. I'm no expert in thermodynamics, but from what I can tell, while air at 30,000 degrees has peak radiation in the UV spectrum, the amount of energy radiated in the visible spectrum is still significant, particulary in the blue-violet region (much like lightning). Now maybe you can create the channel at a lower temperature, but while the amount of energy radiated will be less, more of it will be in the visible spectrum.

[Norade]

Except that the majority of scene actually fits if the projectile masses 600 tons and is moving at roughly 131km/s. The fireball size is too large but that is a possible shield interaction, the fireball duration fits to within an order of magnitude. The only thing that we have to explain is why the round isn't glowing and why the atmosphere isn't on fire and that could be done by saying the used a laser, which could be invisible to the naked eye, to clear a channel for the shot to travel down.

No laws of physic broken, the scene still works, and the MAC gun is still a MAC gun. Unlike your assertion that the shot could be traveling at 0.4c, which it clearly isn't, I can back it up with more than if you're wrong I must be right.

Not sure how hot you have to get air to clear a channel through it, but lightning does it by heating the air to about 30,000 degress C. Depending on how long you have the projectile taking to travel the distance, varying sizes of channels are needed. It the projectile only takes 1/10 of a sec, the channel can have a radius of 0.77 m. If it takes a full second, the channel will have to have a radius of 3.2 metres to allow for the distance the projectile drops. I did some quick calcs and found you'd need about a 44 GW laser for the 1/10 of a sec shot and about 77 GW for a full second with the larger channel.

However, I'm pretty sure this heating of the air by a laser to create a channel would be visible even if the laser is not. It likely will look pretty much like lightning does, except the stroke will be a lot straighter. I'm no expert in thermodynamics, but from what I can tell, while air at 30,000 degrees has peak radiation in the UV spectrum, the amount of energy radiated in the visible spectrum is still significant, particulary in the blue-violet region (much like lightning). Now maybe you can create the channel at a lower temperature, but while the amount of energy radiated will be less, more of it will be in the visible spectrum.

Well there is an explosion and a bright white channel as the shots fire so that could be a potential cover for that aspect of things if we choose that as our explanation of choice.