Spaceships hull armor…solid?

[Witchking]

Originally Posted by Rupert

Their guns were also quite small for their size - a WWII medium tank would have a gun of about 3" bore, and 50-70 calibres long. A WWII battleship would have main guns of 14-18" and about 45-50 calibres long (though they had many more, of course). The latter massed very roughly a thousand times to former.

Of course a lot of that mass is taken up by the difference in operational range.

Heavy Tank Char B1 bis Operational range 200 km

Battleship Richelieu Operational range 17,600 km

Both French, both roughly WW2 vintage. Does point out the vast difference in the amount of mass committed to gas, bullets and beans to be able to operate for weeks/days vs hours.

[Polydamas]

Originally Posted by Agemegos

Battleship guns and armour demonstrated things about impactors with velocity less than about one kilometre per second. The hardness and tensile strength of materials are much less significant when you are dealing with two or three orders of magnitude more kinetic energy per unit mass, and everything behaves in collision like several times its own mass of detonating TNT.

I was really hoping that David Pulver addressed this, he does research so should have an evidence-based opinion on thick layers of armour v. Whipple Shields. The Whipple shield is not a popular trope and most TTRPG spaceships will be governed by tropes rather than realistic extrapolation.

Engineers and physicists who have studied performance in that sphere seem to agree that Whipple shields are the most weight-efficient way to armour spacecraft against impacts as far as this layman can tell.

[Anthony]

Originally Posted by Polydamas

Engineers and physicists who have studied performance in that sphere seem to agree that Whipple shields are the most weight-efficient way to armour spacecraft against impacts as far as this layman can tell.

It's the most efficient way to armor against random incidental impacts. Purpose built missiles are likely to use something like sequential impactors to drill through armor.

[Agemegos]

Originally Posted by Anthony

It's the most efficient way to armor against random incidental impacts. Purpose built missiles are likely to use something like sequential impactors to drill through armor.

That would take pinpoint accuracy, and seems implausible.

[mlangsdorf]

Tandem HEAT warheads already exist, and presumably you can do a similar technique with explosively formed projectiles. If the serial impactors are all carried on the same gyrostabilized delivery device, the required accuracy doesn't seem implausible.

[Fred Brackin]

Originally Posted by Agemegos

That would take pinpoint accuracy, and seems implausible.

Not implausible for guided missiles. You saw something very much like that level of accuracy with laser guided bombs in Iraq.

I doubt it's necessary. Though some people chant "Whipple Shields!" like they were magic words what goes specifically with those words is just a particular implementation of the "spaced armor" principle and one aimed at very small impactors at moderate velocities (when tlkling about space weapons anyway).

The outer layer of the spaced armor must be massive enough that collision with it completely destroys the impactor and the spacing between layers large enough to let the resulting explosion dissipate sufficiently.

There is no magic. If the impactor is too large it won't be completely destroyed and if the total enrgy involved is too high it won't dissipate enough.

[Polydamas]

Originally Posted by Fred Brackin

Not implausible for guided missiles. You saw something very much like that level of accuracy with laser guided bombs in Iraq.

GPS guided bombs are aimed at static targets from free fall not across the relative velocities encountered in spaceship combat, and the targets did not have ECM or the ability to shoot down satellites.

Again, I have never seen an argument that single thick layers of hard dense armour would be a practical scheme for spacecraft armour, whereas there are actual spacecraft which use Whipple shields. Anyone who believes in the first scheme would need to make a case, with the physics.

[Rupert]

Originally Posted by Polydamas

GPS guided bombs are aimed at static targets from free fall not across the relative velocities encountered in spaceship combat, and the targets did not have ECM or the ability to shoot down satellites.

You'd have the impactors on the same delivery bus, and them separate very shortly before impact so the separation is small (in both time and distance).

Again, I have never seen an argument that single thick layers of hard dense armour would be a practical scheme for spacecraft armour, whereas there are actual spacecraft which use Whipple shields. Anyone who believes in the first scheme would need to make a case, with the physics.

And nowhere in Spaceships does it say whether the armour is a single monolithic plate or not. It merely tells us what it's (mostly) made of, how much it masses, and what protection that confers.

I think assuming that it's anything but "whatever works well against the threats the ship faces" (whatever form of armour that might be) is mistaken. "Whatever works best" would of course be the 'hardened' option, at double cost.

[Polydamas]

Originally Posted by Rupert

You'd have the impactors on the same delivery bus, and them separate very shortly before impact so the separation is small (in both time and distance).

But at astronomical velocities, even 1/100 of a second could make it hard to hit the same hole. And if they are too close together they will be hit by debris from the first projectile vapourizing and be knocked off course.

Originally Posted by Rupert

I think assuming that it's anything but "whatever works well against the threats the ship faces" (whatever form of armour that might be) is mistaken. "Whatever works best" would of course be the 'hardened' option, at double cost.

But the way single hard dense layers of armor scale against bullet-speed projectiles is different than the way Whipple shields scale against astronomical-speed projectiles. A model has to make some assumption about how armour and threats scale against each other.

[Anthony]

Originally Posted by Polydamas

But at astronomical velocities, even 1/100 of a second could make it hard to hit the same hole.

I was more interested in whipple shields, where you would expect an initial impact to make a pretty large hole.