Spaceships hull armor…solid?

[Agemegos]

Originally Posted by Anthony

Many small projectiles would not penetrate a whipple shield, but they would destroy it.

Yes, they would. And if those same small projectiles at the same velocity were to impact a solid slab they would destroy and penetrate a thickness of it that had a mass many times greater than that of the Whipple shield.

I do not claim that Whipple shields make a spaceship invulnerable. I merely claim that against hypervelocity impactors they are several times more effective than an equal mass of any solid armour, regardless of the solid armour's strength and hardness.

Yes, one of you mylar balloons or one of Fred's claymore mines will remove several square metres of the outer few layers of a suitably spaced armour, making an area vulnerable to a follow-up attack. But if either of them were to impact solid armour plate they would make a hole in that just as big or bigger, rupture the pressure containment, and spray high-velocity debris in a plume through the interior of the ship.

[Fred Brackin]

Originally Posted by Agemegos

I do not claim that Whipple shields make a spaceship invulnerable. I merely claim that against hypervelocity impactors they are several times more effective than an equal mass of any solid armour, regardless of the solid armour's strength and hardness.

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Then I guess we're done here because no one arguing ikn favor of slab armor.

Some of us do mind all spaced armor being reduced to "Whipple shields". Spaced armor designed for effectiveness agaisnt a 40 cm missile at 20 miles per second isn't going to look much like what's on that space probe.

[Anthony]

Originally Posted by Agemegos

Yes, one of you mylar balloons or one of Fred's claymore mines will remove several square metres of the outer few layers of a suitably spaced armour, making an area vulnerable to a follow-up attack. But if either of them were to impact solid armour plate they would make a hole in that just as big or bigger, rupture the pressure containment, and spray high-velocity debris in a plume through the interior of the ship.

If you make your bubble grossly excessively massive, yes, but why would you do that? You want an impactor that's just heavy enough to cause the surface layer to shatter; if it hits a surface layer that's ten times heavier, it's not actually going to do much.

This actually introduces a fair amount of information warfare into the equation: if you know how thick your enemy's armor is, you can tune your warhead to match (it will generally be faster to change warheads than to change armor), if you get it wrong you're going to suffer a significant effectiveness penalty.

[Agemegos]

Originally Posted by Anthony

If you make your bubble grossly excessively massive, yes, but why would you do that?

To destroy the spaceship with solid armour — at less expense and difficulty than is required to remove one layer of spaced armour from a ship with a Whipple shield.

Famously, if a one-inch ball bearing were to collide at thirty kilometres per second with a spaceship that had solid armour, it would make the armour (and anything else) in a channel one inch wide and six feet long explode with the energy of 20 kilograms of detonating TNT. That's much more effective and easier to arrange than removing the layers of a Whipple shield one by one using sequenced collisions with diaphanous wisps of mylar.

[Anthony]

Originally Posted by Agemegos

Famously, if a one-inch ball bearing were to collide at thirty kilometres per second with a spaceship that had solid armour, it would make the armour (and anything else) in a channel one inch wide and six feet long explode with the energy of 20 kilograms of detonating TNT.

No it wouldn't. The channel would be a couple inches deep, not six feet (exact depth depends on mass ratio but is usually irrelevant due to being less than the crater depth).

You do want spaced armor, but that doesn't mean whipple shields, it means fairly substantial layers.

[Agemegos]

Originally Posted by Anthony

No it wouldn't. The channel would be a couple inches deep, not six feet (exact depth depends on mass ratio but is usually irrelevant due to being less than the crater depth).

You are failing to take the momentum of the impactor into account, and you are making too much of the rigidity of the armour. A hypervelocity impact is not analogous to an explosion on the surface by a contact-fuzed explosive.

The strength and hardness of the armour and impactor are irrelevant compared with the energies involved. The impactor behaves like the jet or penetrator formed by a HEAT warhead, except even more so, and it penetrates deeply. It produces a narrow channel of violently shocked and evaporated armour that indeed expands sideways, but does so slowly compared with the velocity of the initial impact, Also, the shocked armour material picks up momentum from the impactor, which tends to tamp it into the channel.

HEAT warheads (that detonate at the proper standoff and in the correct orientation) do not produce wide superficial craters. Neither will this, and for the same reason except more so.

Yes, the hypervelocity impactor can be stopped by a sufficient depth of material. It will slow as it penetrates to the point where material strength is significant, and then stop. Then you enter into the time scale in which the material it has rammed through can transfer energy to the surrounding armour. In that phase it is as though the penetration channel were exploding. So if your armour is thin compared with the depth that the impactor can penetrate (armour mass being significant but armour strength much less so in determining the depth of potential penetration) you get a narrow channel that widens towards the back, and a plume of debris behind the armour.. If the armour is thick compared with the potential penetration, the impactor does not bounce off or shatter like and artillery shell. It penetrates deeply into the armour, and the debris that would otherwise have produce the plume instead explodes in the penetration channel. That will only make a surface crater if the armour is very thick indeed. With armour less than about a couple of hundred times as thick as the impactor is long (for a 30 km/s impact) it will blast a ragged hole.

[Anthony]

Originally Posted by Agemegos

You are failing to take the momentum of the impactor into account

The momentum really doesn't matter -- at these velocities you're just looking at colliding fluids and penetration barely changes across a range of something like 10 to 10,000 km/s, it's just about length and density of the penetrator relative to the thickness and density of the armor.

What happens is that, by the time the penetrator has encountered total mass equal to its own, it will have turned into a spray expanding at around 60 degrees and the resulting plasma is moving at half speed. As it continues, it mixes with more and more armor mass, and spreads faster and faster, so it's going to slow down to subsonic velocities in only a couple projectile lengths.

The way you improve penetration (which is what HEAT and long rod penetrators do) is by having a thin jet, which therefore takes longer to encounter its own mass in armor.

[Fred Brackin]

Originally Posted by Agemegos

The strength and hardness of the armour and impactor are irrelevant compared with the energies involved. The impactor behaves like the jet or penetrator formed by a HEAT warhead, except even more so, and it penetrates deeply. It produces a narrow channel of violently shocked and evaporated armour that indeed expands sideways, but does so slowly compared with the velocity of the initial impact, e.

I would only expect such behavior only at velocities below that needed for meteoric explosion. When the velocity of impact is enough to blow both the impactor and the outer layer of armor into a plasma that's even hotter than that of detonating high explosive it's going to expand like high explosive and the net momentum of armor and impactor will be seen only over the whole explosion.

[Agemegos]

Originally Posted by Fred Brackin

I would only expect such behavior only at velocities below that needed for meteoric explosion. When the velocity of impact is enough to blow both the impactor and the outer layer of armor into a plasma that's even hotter than that of detonating high explosive it's going to expand like high explosive and the net momentum of armor and impactor will be seen only over the whole explosion.

That’s not what is found when engineers test it. Actual spacecraft such as the ISS are built with (multi-bump, stuffed) Whipple shields and not with monolithic slab armour because hypervelocity impacts are in fact not only grossly energetic but also penetrating. Superficial explosions are not observed in tests, and actual rocket scientists don’t plan for them. Your expectations notwithstanding.

[Fred Brackin]

Originally Posted by Agemegos

That’s not what is found when engineers test it. Actual spacecraft such as the ISS are built with (multi-bump, stuffed) Whipple shields and not with monolithic slab armour because hypervelocity impacts are in fact not only grossly energetic but also penetrating. Superficial explosions are not observed in tests, and actual rocket scientists don’t plan for them. Your expectations notwithstanding.

Every time I hear things like this there is _never_ any mention of velocity.

What I expect from "armor" for the ISS is testing within and preparation for a relatively low range of velocities and impactor sizes i.e what they expect to see in this specific case.