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Old 04-29-2021, 03:37 PM   #1
the-red-scare
 
Join Date: Sep 2014
Default [Spaceships] Armor and Volume expanded

This is just a generalization of the armor volume rules from Pyramid.

Each system now has a value for volume. A standard vessel with the stats listed in the Spaceships books would have a volume of 20, or 1 per system. Vessels with more or less volume have a few different stats, notably dDR and physical SM for targeting. Vessels always retain their design SM for other uses, such as Accel. Systems have the following volume numbers.

Ice Armor, Rock Dust, Stone Armor, Water: 0.3
Ablative Plastic, Comm/Sensor Array, Coolant, Control Room, Jet Fuel, Nuclear Pellets: 0.5
Rocket Fuel: 1.5*
Hydrogen: 5
Open Space: var.**
All Other Armor: 0
Everything Else: 1

* This is Spaceships standard hydrogen-oxygen rocket fuel. Kerosene-oxygen (0.11 mps per tank) would be 0.5, and I believe methane-oxygen is pretty close to that as well. This is one of the reasons to use those fuels despite their lower specific impulse, and would be more relevant if Spaceships accounted for frame and tankage mass.

** Open Space systems are not scaled like anything else, and their volume is going to depend on your assumptions about just what an open space really is. The basic model is to call them farms from Space 3e or Transhuman Space. This makes them 500 "spaces" (or Traveller dtons) per 0.05-acre open area. To calculate their volume, take the number of open areas as listed in Spaceships and multiply by 50,000, then divide by the vessel's Lwt. Proportionally, Open Spaces are much larger on smaller vessels.

Add up the systems to get the volume for the vessel. The physical SM of the vessel (for targeting, or for estimating its dimensions, cost of surface features, etc.) is modified by rounding the volume up to the next whole number and consulting the table below.

1: -3
2: -2
3-6: -1
7-20: 0
21-60: +1
61-200: +2
201-600: +3

This is a direct translation of the standard SM rules where if a value is between two options you round up. There will always be an awkward bit at the break points. If it feels better you could shift the cutoff to follow a 1-3-10 or 1.5-5-15 progression, as long as 20 always results in no change.

If this were a book, here would be a table to look up the effect on dDR, but I don't feel like doing the work. To calculate dDR, divide the volume by 20, then take the cube root of that value and square it. Finally divide 1 by that value and multiply the result by the dDR on the Armor table in Spaceships for the design SM for the ship (not any new physical SM), rounding down.

Example 1: Prospero-class Interplanetary Liner (Spaceships 2)

3x armor (0)
4x hydrogen (20)
1x SM +8 open space (1 x 50,0000 / 1,000 = 50)
12x other (12)

Total volume is 72. This is between 61 and 200, so the physical SM increases two levels to SM +10. dDR is 1 / ((72/20)^(2/3)) = 0.43 x 10 = dDR 4.

Example 2: Victory-class Space Cruiser (Spaceships 3)

6x armor (0)
5x nuclear pellets (2.5)
9x other (9)

Total volume is 11.5. This isn't enough to reduce the physical SM of the ship. dDR is 1 / (11.5/20)^(2/3)) = 1.5 x 150/50/100 = dDR 225/75/150.
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