Spaceships hull armor…solid?

[Agemegos]

Originally Posted by Anthony

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.

If it collided isothermally with an equal mass in vacuum, yes, Confined into a channel by surrounding armour material that cannot accelerate laterally fast enough to get out of the way, and converting kinetic energy to heat rather yhan expansion, no. The jet of impactor and armour debris spreads out less than you figure; more of its energy is converted to heat than you figure, and less to the kinetic energy of expansion. The penetration is narrower and deeper than you figure, and the explosion is delayed.

[Agemegos]

Originally Posted by Fred Brackin

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.

Don’t expect, Fred. Read the reports. I linked them in a similar discussion with the same participants fourteen years ago.

[Anthony]

Originally Posted by Agemegos

That’s not what is found when engineers test it.

No-one has actually tested a situation particularly relevant to what we're talking about, because meteor impacts are random, not directed by a hostile intelligence. You definitely want spaced armor (which is in fact what a whipple shield is), but the exact weight and spacing of the layers you want is dependent on the threats you're expecting.

Originally Posted by Agemegos

If it collided isothermally with an equal mass in vacuum, yes, Confined into a channel by surrounding armour material that cannot accelerate laterally fast enough to get out of the way, and converting kinetic energy to heat rather yhan expansion, no.

At 30 km/s, that surrounding armor is really not doing anything to prevent expansion.

[Fred Brackin]

Originally Posted by Agemegos

Don’t expect, Fred. Read the reports. I linked them in a similar discussion with the same participants fourteen years ago.

Or you could look at the face of the Moon. That isn't covered with deep narrow craters caused by jet-like penetrations. There are obviously some limitations to the principle.

As to your reports I suppose I'm decent at Google Fu but your starting place s a little too thin for me.

[Polydamas]

Here are some papers on Whipple Shields. I am going to read them and learn from them. If people want to keep exchanging rhetoric in defense of their preconceptions, that is OK too!

"Status and Perspectives in Protective Design" Space Debris 2 (2000) https://link.springer.com/article/10...29884.04355.9a (can be dowloaded from a university library or other places)

"Hypervelocity Impacts and Protection" which seems to be some kind of technical report or working paper from the European Space Agency and is dated 2001 https://www.researchgate.net/publica...and_Protection (can be downloaded by anyone with a browser)

Edit: Pai, A. ; Divakaran, R. ; Anand, S. ; Shenoy, S. B. "Advances in the Whipple Shield Design and Development: A Brief Review." Journal of dynamic behavior of materials, 2021, Vol.8 Nr. 1, pp. 20-38 https://link.springer.com/content/pd...70-021-00314-7 (seems to be open access) Regarding the claim that tests focus on a narrow range of velocities and impactors, they state that most tests examine velocities from 3 to 18 km / s

[Fred Brackin]

Originally Posted by Polydamas

Here are some papers on Whipple Shields. I am going to read them and learn from them. If people want to keep exchanging rhetoric in defense of their preconceptions, that is OK too!

"Status and Perspectives in Protective Design" Space Debris 2 (2000) https://link.springer.com/article/10...29884.04355.9a (can be dowloaded from a university library or other places)

"Hypervelocity Impacts and Protection" which seems to be some kind of technical report or working paper from the European Space Agency and is dated 2001 https://www.researchgate.net/publica...and_Protection (can be downloaded by anyone with a browser)

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. At least there was some mention of velocities but the highest mentioned was 7 km/s which was probably about the limit for the hydrogen gas guns they mentioned. There have been some tests with railguns that produce much higher velocities.

In particular the expansiosn their pictures showed were more in the area of "mildly elliptical" rather than narrow and jet like. this may have been achieved by use of a very light outer layer which was not substantial enough to fully destroy the impactor. This strategy would be pretty impactor size dependant and not practical in combat.

Among other complications users would want their armered hulls to offer some protection from directed energy weapons and those very thin layers would not be very useful against a rapidly pulsed laser. A thin layer would probably stop only one pulse. A thicker ablative material might be more desirable.

[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.

[Anthony]

Originally Posted by FrackingBiscuit

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.

Yes and no. The problem is not that the analysis for spherical impactors is wrong. The problem is that people interested in space combat are not going to use spherical impactors, nor are they going to use anything close to the mass ranges most of those studies use.

[FrackingBiscuit]

Originally Posted by Anthony

Yes and no. The problem is not that the analysis for spherical impactors is wrong. The problem is that people interested in space combat are not going to use spherical impactors, nor are they going to use anything close to the mass ranges most of those studies use.

Hence my comment about talking past each other...

[Fred Brackin]

Originally Posted by FrackingBiscuit

So by just changing the outer shell to a half-inch plate of aluminum, which shouldn't weigh very much at all, ].

In Spaceships aluminum is "Light Alloy TL7" and it generally gives 50% more dDR per 5% of ship's mass used as armor. On that basis (comparing aluminum to the Gurps standard RHA) 1/2 inch of aluminum should give something like dDR3 (or 30 in regular Gurps).

For an SM+6 ship (100 tons like the Space Shuttle) dDR 3 is what an unstreamlined ship gets for 5% of its' mass as armor. A streamlined vehicle would need more mass than that to hit dDR3 (but Whipple plating doesn't usually work very well with streamlining)..

So half an inch of aluminum would be only _part_ of a armor layer on a much bigger ship.

So covering your outer hull with half an inch of aluminum is only "not very much at all" on very large Spaceships. On small sapceships it's an entire armor module all by itself.