Spaceships hull armor…solid?

[FrackingBiscuit]

Originally Posted by Fred Brackin

Okay, I read the second one (no, I do not spend my evenings in a universiy library) and I did not see a lot of the claims made being justified.

I think part of the problem is that you guys are talking past each other and don't actually know what the other person is saying. Because I just read the paper as well, and reviewed this entire thread, and tracked down the 14-year-old thread Agemegos mentioned (don't look at me like that, I was bored), and everything (including this paper) seems to show that hypervelocity impacts against Whipple shields go exactly as he described.

A spherical impactor hits the outer plate and punches a hole through it barely wider than the impactor itself. The impactor also breaks up into a shower of fragments, which are allowed to expand outwards within the gap between plates. Whatever they impact next - either a second standoff plate or the backing/hull of the spacecraft - they do so over a much wider area, dispersing their energy.

Hitting the standoff plate doesn't absorb energy so much as divide it, so it's possible for fragments to have enough energy to continue penetrating. As the paper demonstrates, and as Agemegos said, the answer they came up with to this problem is to include more standoff plates. Figure 8 demonstrates this visually with Whipple shielding designed for the Columbus module of the ISS, which began to introduce more layers of aluminum as well as materials like Kevlar. Between 1986 and 1994, the Whipple shielding went from protecting the module against impactors up to 4mm in diameter to 13mm in diameter.

Most of the rest of the paper is pointing out useful materials for Whipple shielding and suggesting ways of better simulating hypervelocity impacts. I don't see how any of this disagree with anything Agemegos said.

As far as impactors behaving like thin jets, that was in reference to two specific scenarios, both of which amount to the impactor not having enough time or lateral velocity to break up before it crosses the standoff distance. Either the plate is so lightweight it doesn't cause the impactor to break up enough, or the impactor hits a slab of monolithic armor where its lateral expansion is constrained by the armor material itself. The latter is exactly what makes Whipple shielding (and spaced armor in general) effective - it gives a projectile room to break up after an initial impact. The former problem is a matter of a specific instance of Whipple shielding not being effective against a specific impactor, not of Whipple shielding simply being ineffective as a concept in a certain regime.

As a matter of fact, Agemegos - 14 years ago - used an example of a Spaceships 24cm electromagnetic gun firing at 8km/s. He showed the difference between an aluminum standoff plate of 1mm (where the 24cm projectile hardly broke up at all and resembled a high-speed jet) to a plate of ~13mm, which was massive enough to cause the 24cm projectile to explode into a rapidly-expanding ball of 12,000-kelvin plasma, which was much less penetrating. So by just changing the outer shell to a half-inch plate of aluminum, which shouldn't weigh very much at all, Agemegos was able to create a Whipple shield that was effective against a Spacehips SM+10 major battery. Considering Spaceships gives electromagnetic guns a minimum effective velocity of 2mps (I believe it was higher all those aeons ago), this is slightly more than the minimum damage of a 56cm electromagnetic gun (that's a SM+15 major battery), and equal to a 40cm missile impacting at 3mps, which could actually be reasonable for a standard missile against an evasive target. This is with a half-inch aluminum plate and a 1 meter gap to the next surface.

The takeaway is that Whipple shielding ~of some variety~ can be effective to some degree against the guns of any size ship you can build with Spaceships.