Spaceships hull armor…solid?

[briansommers]

Noob here.

I’m I to understand correctly that armor on spaceships is solid and not a layer added to the outside?

So, there’s front, center, rear hull areas each consisting of 6 areas each?

So when I add armor to any of the 18 sections of the hull, I can’t put anything else in there correct?

[weby]

The spaceships system is one that calculates mass not volume.

There are a total of 20 systems.
6 front, 6 center, 6 rear and 2 core systems

If you put in armor that takes one of the 20 slots as armor has significant mass thus each such mass unit takes one of the mass slots and provides the armor value given in the table into that section.

[Phantasm]

Originally Posted by weby

There are a total of 20 systems.
6 front, 6 center, 2 rear and 2 core systems

Pretty sure this is a "changed my thought halfway through"; it's 6 rear, not 2.

But yes, an armor module - like all modules - takes up 5% of the ship's overall mass.

[The Colonel]

I'm guessing there are no Washington Treaty style shenanigans then with using the ship's bulk water tanks as armour or what have you...

[Fred Brackin]

Originally Posted by The Colonel

I'm guessing there are no Washington Treaty style shenanigans then with using the ship's bulk water tanks as armour or what have you...

That's Radiation PF rather than DR. You cna have Ice armor I think.

[The Colonel]

Originally Posted by Varyon

I don't think there are any rules for doing so, no. Spaceships doesn't directly track the weight of water (presumably, it's included in the mass of any system that provides life support), but you could probably work something out (I believe water canonically grants around DR 1 per inch).

Originally Posted by Fred Brackin

That's Radiation PF rather than DR. You cna have Ice armor I think.

I would imagine that a water tank should also meddle with directed energy beams as well - 1DR/inch sounds fine for kinetic hits, but I have no notion what it would do to laser, plasma or charged particle beams...

[weby]

Originally Posted by Phantasm

Pretty sure this is a "changed my thought halfway through"; it's 6 rear, not 2.

But yes, an armor module - like all modules - takes up 5% of the ship's overall mass.

Indeed, wrote the thing in a different order first but was less clear so then had a copy paste error on rewrite.. :)

[Polydamas]

When I saw the original thread topic, I thought it was about whether the GURPS Spaceships rules assume thick solid armour like in space opera or Whipple Shields like on some real spacecraft.

There are some quibbles whether spaceships with a lot of armour should have their SM reduced because so much mass is in high-density armour, but any simple rule has limits.

[Varyon]

Originally Posted by Polydamas

When I saw the original thread topic, I thought it was about whether the GURPS Spaceships rules assume thick solid armour like in space opera or Whipple Shields like on some real spacecraft.

I don't think there's an option for Whipple Shields anywhere in Spaceships. Such probably wouldn't count as high-density systems anymore, but would have much better performance against hypervelocity impactors.

Originally Posted by Polydamas

There are some quibbles whether spaceships with a lot of armour should have their SM reduced because so much mass is in high-density armour, but any simple rule has limits.

As I mentioned upthread, Pyramid #3/34 has official rules for this. Basically, if you have 25% (5 systems) or more of armor, the surface area of the vessel decreases enough that a given mass of armor actually gives more protection. If you have 60% (12 systems) or more of armor, the volume of the vessel decreases enough for an outright reduction of -1 to SM. If you have 90% (18 systems) or more of armor, the volume of the vessel decreases enough for an outright reduction of -2 to SM.

[Varyon]

As noted, each system is 5% of the mass of the ship, so if you assign one as armor, said armor has a mass equal to 5% that of the ship, and you only have 95% to work with for the rest of it. Said armor systems are spread over that section of hull, however - that dDR protects everything (except for Exposed Systems, naturally) in the same section where it is set.

Armor is incredibly dense, however, so there are some optional rules in Pyramid #3/34 to account for this - having a lot of armor makes your vessel smaller, which increases the effectiveness of armor (less surface area to cover means thicker armor for a given mass), and can even make your vessel harder to hit (-1 or -2 to SM, due to being rather small compared to less-armored vessels of the same mass). Personally, I also don't see a serious issue with allowing armor to be added on in excess of the 20-system limit, but if you do so you'll need to adjust acceleration and delta-v. For example, let's say you've got a ship - 2G acceleration, 9 fuel tanks, total delta-v 31.5 mps - where all the systems are already taken up, but you decide to toss on another 3 armor modules (one for each section) to increase dDR. Your ship is now 115% - 23/20 - of the mass that its drives were designed for. You would divide acceleration by this ratio, giving you around 87% of your originally-calculated acceleration - around 1.7G. For delta-v, you would actually divide your number of fuel tanks by this ratio, then recalculate delta-v from there. 9 fuel tanks becomes 7.8 fuel tanks, which works out to only 23.4 mps delta-v (9 fuel tanks has a multiplier of x1.4, but 7-8 fuel tanks only has a multiplier of x1.2, hence the loss of more than 13% of your delta-v).

Making a vessel extremely heavy by piling on armor should make it harder to handle, as your Control Room (or, rather, the attitude gyros/thrusters/etc that actually make up the bulk of the Control Room's mass) is too small. -1 to Hnd if you're 150% mass (10 extra armor systems) or larger; at 300% mass (40 extra armor systems), you should just redesign the vessel to be one SM larger, but with enough armor to be targeted as a smaller vessel.

Originally Posted by The Colonel

I'm guessing there are no Washington Treaty style shenanigans then with using the ship's bulk water tanks as armour or what have you...

I don't think there are any rules for doing so, no. Spaceships doesn't directly track the weight of water (presumably, it's included in the mass of any system that provides life support), but you could probably work something out (I believe water canonically grants around DR 1 per inch).