Approximating High-Tech and Ultra-Tech with Spaceships

[Michael Thayne]

Originally Posted by The_Ryujin

The armors in Spaceships are, as far as I can tell, based on the simple Ultra-Tech assumption that TL9 armor has a WM of 0.135, TL10 armor has a WM of 0.09, TL11 has a WM of 0.06 and TL12 has a WM of 0.4. Also keep in mind that the numbers tend to be rounded off a lot in these books.

To give you an example, the baseline idea for the ships in the series were that they were unstreamlined cylinders like most of the ships in Transhuman Space.

A SM +5 30 tons ship is 45ft long and would have a volume of 3,000 cubic feet. This means that it's end caps are about 9ft across. This gives it a a surface area of ~1,436 square feet.

Now in order to completely cover a ship, you need 1 armor in each of a ships three sections. For a 30tons ships this means it would need 9,000lbs of armor to match the values to match the armor stats listed in the books.

If we give the ship TL9 Advanced Metallic Laminate, at SM+5 it would have DR50 which whould weight 1,437×50×0.135 = 9,692lbs... a bit much but not that far off.

However there's a reason for this.

GURPS normally follows a 1.5 based progression and since TL10 Nanocomposite would give it DR70, TL9 armor should give it only ~DR46.7. Plugging that into the equation gives us 9,052lbs. A close enough match!

At TL10, Nanocomposite would give it DR70 and a WM of 0.09 which gives us 9,046lbs. Once again, right about on target.

TL11 Diamondoid would give it DR100 and a WM of 0.06. This gives us only 8,615lbs worth of armor but one again if we follow the 1.5 progression then diamondoid should have DR105 and that gives us 9,046lbs again!

TL12 Exotic Laminate has DR 150 and a WM of 0.04 which gives us a final weight of 8,615 again and as you probably have guess by now it's DR should be 157.5 which once again gives 9,046lbs.

So if you want to custom armor you spaceships, remember that they got the surface area of cylinder that has a volume of (ships weight in pounds/20) cubic feet.

How did you get that volume figure? It looks like you're assuming a density of 20 lbs. per cubic foot. However, that 30 ton weight statistic is loaded weight. Water is about 60 lbs. per cubic foot. Few common materials are 1/3 the density of water, 40% to 120% is more common for hydrocarbons and organic matter. And an ore hauler will be hauling cargo significantly more dense than water—silica is 2.65x as dense as water, metals can be 8x as dense as water or more. So if you're looking to make an assumption about spaceship density, assuming 60 lbs. per cubic foot is probably better as a simplified approximation.

(In the end, though, you seem to have reached a similar conclusion to what I did about Spaceship armor WM. Probably a good mathematical reason for this that I'm too lazy to figure out right now.)