Spaceships hull armor…solid?

[Varyon]

Originally Posted by Fred Brackin

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.

Note that's dDR 3 on only 1/3rd of the vessel; to cover an entire SM+6 spaceship with half an inch of aluminum, you're looking at 15% of the ship's mass being armor. Meanwhile, for an SM+10 unstreamlined vessel, where each module of light alloy armor provides dDR 15 to 1/3rd of the vessel, you could get away with roughly 3% of the vessel's mass to get that half-inch layer of aluminum over the entire surface (1 module - 5% of mass - over the entire surface would provide dDR 5, and we only need 3/5ths of that).

[Polydamas]

Very many visions of space warfare involve ball bearings, birdshot, or other spherical projectiles (remember "To be slightly more military-minded you can make something like a claymore mine only loaded with the smallest birdshot"?), and the only way to test whether other shapes would work better is to sit down and calculate, calculate, calculate.

(Obviously NASA and the ESA do not envision being hit by perfect spheres either, but it simplifies the calculations and irregular space junk is likely to be less effective than those spheres; I suspect there is a paper out there on the possibility 'what if a bolt or screw hits small-end-on?')

Edit: for those following along at home, the claim which I show is not justified is "people interested in space combat are not going to use spherical impactors". A lot of people speculating about how combat in space might work do assume spherical projectiles, and to show that any other shape would perform better against Whipple shields (without simultaneously performing better against homogeneous slab armour) you need to sit down and calculate, calculate, calculate.

[Fred Brackin]

Originally Posted by Polydamas

Very many visions of space warfare involve ball bearings, birdshot, or other spherical projectiles (remember "To be slightly more military-minded you can make something like a claymore mine only loaded with the smallest birdshot"?), and the only way to test whether other shapes would work better is to sit down and calculate, calculate, calculate.

That was not to penetrate Whipple plating. That was to scrub the outer layer of it away. For military applications there's no need to liimit yourself to doing it all in one shot.

[FrackingBiscuit]

Originally Posted by Fred Brackin

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.

Okay? Most designs in the Spaceships books themselves are at least 15% armor. A SM+6 space shuttle with the standard 15% armor already has most of the mass needed to protect against SM+10 ship railguns. That's canonical generic space shuttles with TL7 armor being able to survive cruiser-sized TL9 guns. Move it up one SM or one TL and it's more than enough mass to survive the same gun. So yeah, for what it's getting I'd say that's not very much at all.

If you think one armor system per section is excessive for a ship built to survive combat against space cruisers, I don't know what to tell you. At that point it sounds like you're just being contrarian.

[Fred Brackin]

Originally Posted by FrackingBiscuit

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If you think one armor system per section is excessive for a ship built to survive combat against space cruisers, I don't know what to tell you. At that point it sounds like you're just being contrarian.

I interpreted your "not very much at all" as "negligable" rather than "affordable".

Many people are .....odd about Spaceships armor and don't seem to understand the scales involved or why armoring strategies that (sort of, kind of) worked for WWI-WWII cruisers and battleships don't work so well in space.

However if you are aware that 2 armor systems (the 1/2 inch aluminum layer and then the backing) are needed along with a lot of space between them then everything's fine. Turning the impactor into plasma as far away from my inner hull as possible has always been what I wanted spaced armor to do.