Spaceships hull armor…solid?

[Agemegos]

Originally Posted by Anthony

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

They don't make large holes. The impacts in the outer layers of Whipple shields make tiny holes, barely bigger than the impactors. I've seen photographs from experiments.

The reasons are that:

(1) The shields are deliberately made of material that is too weak and not rigid enough for destructive shockwaves to propagate through them. It evaporates locally but does not transmit much energy through itself.

(2) The momentum of the impactor is conserved in the debris, producing a cloud that continues into the space behind the first layer faster than it expands, i.e. a narrow jet rather than a spherical cloud. The explosion of the impactor and the bit of the first layer that it actually intersects effectively takes place behind the first layer of the shield, not within it, because of momentum.

[Anthony]

Originally Posted by Agemegos

They don't make large holes. The impacts in the outer layers of Whipple shields make tiny holes, barely bigger than the impactors.

So for your initial impactor use an inflated mylar bubble. Or various things designed to destroy a layer like that, such as a bundle of string. The core problem is that the whipple shield can't be particularly firmly attached to the main hull, so it doesn't take that much energy to destroy it.

[Fred Brackin]

Originally Posted by Anthony

So for your initial impactor use an inflated mylar bubble. Or various things designed to destroy a layer like that, such as a bundle of string.

To be slightly more military-minded you can make something like a claymore mine only loaded with the smallest birdshot. Detonate that just before impact and you can scrub large areas of light armor off the hull.

[Agemegos]

Originally Posted by Anthony

So for your initial impactor use an inflated mylar bubble. Or various things designed to destroy a layer like that, such as a bundle of string. The core problem is that the whipple shield can't be particularly firmly attached to the main hull, so it doesn't take that much energy to destroy it.

And the core problem with monolithic slabs is that it doesn’t take much mass to have enough energy to destroy it. Your mylar balloon will penetrate a thick slab of the strongest solid just as well as a curtain of nylon tulle. The nylon tulle is much easier to wear forty of.

[Polydamas]

And come on guys: NASA says that their Stardust probe in the link above is proof against impactors up to 1 cm. Wiki says that its largest dimension is 1.7 metres, I think that is length and the armoured side is the 0.5 by 0.5 metre side. So clearly an impactor is not going to make more than a 0.5 metre hole.

Intuition does not work at astronomical velocities, you need either experiments (must be lots of them online or in libraries) or math.

[Fred Brackin]

Originally Posted by Polydamas

And come on guys: NASA says that their Stardust probe in the link above is proof against impactors up to 1 cm.

So let's see if Spaceships uses projectiles as _small_ as 1 cm.

<run and go look> No, it doesn't. The smallest possible projectile (for a VRF gun) is 2cm. Missiles start at 16 cm and go way up.

There is also no speed limit (except c) but that NASA shiled was made to handle particles up to 1cm at the relative speed seen in that comet approach. Whatever that is, I didn't see speed mentioned but speed is crucically important in Spaceships..

Anyway, we do seem to have cleared up that Whipple shields are not efffective armor in Spaceship because they can't handle typical sizes of projectiles.

[Polydamas]

Quoth Fred:

Originally Posted by Fred Brackin

To be slightly more military-minded you can make something like a claymore mine only loaded with the smallest birdshot. Detonate that just before impact and you can scrub large areas of light armor off the hull.

Quoth Fred seven hours later:

Originally Posted by Fred Brackin

So let's see if Spaceships uses projectiles as _small_ as 1 cm.

<run and go look> No, it doesn't. The smallest possible projectile (for a VRF gun) is 2cm. Missiles start at 16 cm and go way up.

...
Anyway, we do seem to have cleared up that Whipple shields are not efffective armor in Spaceship because they can't handle typical sizes of projectiles.

So Fred literally went in seven hours from "many tiny projectiles could beat Whipple shields" to "its not fair to talk about many tiny projectiles because the smallest gun in GURPS Spaceship says 2 cm."

Come on man! You are acting like a 14 year old arguing whether Batman could beat Spiderman. Come back when you are willing to talk like an adult.

(Obviously, the fact that one real spacecraft has a Whipple shield designed to stop 1 cm impactors says nothing about what types of impactors other whipple shields can or could stop).

[Anthony]

Many small projectiles would not penetrate a whipple shield, but they would destroy it. Of course, at space combat velocities and energies any armor is fundamentally ablative, but there's a difference between vaporizing and breaking into bits and letting the bits drift away, and I would expect whipple shields to be relatively more vulnerable to the latter.

[Fred Brackin]

Originally Posted by Polydamas

(Obviously, the fact that one real spacecraft has a Whipple shield designed to stop 1 cm impactors says nothing about what types of impactors other whipple shields can or could stop).

Then why did you bring it up?

[Anthony]

Many small projectiles would not penetrate a whipple shield, but they would destroy it. Of course, at space combat velocities and energies any armor is fundamentally ablative, but there's a difference between vaporizing and breaking into bits and letting the bits drift away, and I would expect whipple shields to be relatively more vulnerable to the latter.