House rules for gravity

[Agemegos]

Okay, my previous uncertainty about GURPS' rules for unfamiliarity and experience with different amounts of gravity has been cleared up by the grace of KROMM. Now that I understand the rules I am of the opinion that they don't suit my desires, in four respects.

1. I find basing everything off the character's home gravity rather fiddly.
2. I don't like the way that gravity increments based on the gravity with which the character has G-familiarity can fail to overlap with those based on his or her home gravity, producing queer little gaps and overlaps.
3. I don't like the fact that a character can never become fully familiar with a new gravity.
4. I dislike the rules that make a character with a low home gravity just worse than one with a high home gravity when it comes to IQ, HT, and FP modifiers. They present an undesirable incentive to players, and I don't even know that they are particularly realistic.

Your mileage may vary.

I propose to do something like the following in my campaign. I'd appreciate it if GURPS boffins would point out any problems or weaknesses in my suggestion and suggest improvements.


I propose to establish fixed G-increments that are not based on any character's home gravity, as follows.

*0.1 – *2.0 ms^-2
*2.+ – *4.0 ms^-2
*4.+ – *6.0 ms^-2
*6.+ – *8.0 ms^-2
*8.+ – 10.0 ms^-2
10.+ – 12.0 ms^-2
12.+ – 14.0 ms^-2
14.+ – 16.0 ms^-2
etc.

Below 0.1 ms^-2 the rules for the Free Fall skill are used instead of these rules.

Note that one gee is 9.81 ms^-2. That means that 2.0 ms^-2 is close to 0.2 gee, and that one gee is in the increment 8.1 – 10.0 ms^-2. Note further that shirtsleeve-habitable planets produced by the GURPS Space star system generation sequence have surface gravities from 4.3 ms^-2 to 12.5 ms^-2. 1 ms^-2 = 3.28 ft./sec./sec. or 1.094 yd./sec./sec.

A character starts out with a -0 DX modifier in the increment he or she grew up in, a -1 DX modifier in adjacent increments, -2 in increments adjacent to thse, and so forth. This modifier is applied to DX rolls and DX-related skill rolls that involve athletic movement (including mêlée attacks, blocks, parries, and dodges, and ranged attacks in turns in which the character moved (including dodging)) or which involve judging the ballistic trajectory of an object. It is not applied to DX-related skill rolls that involve manual work rather than athletic movement, such as for instance Sewing or Knot-Tying. Nor is it applied to ranged attacks in which reflexively judging the fall of the projectile is irrelevant (point-blank shooting, precision aiming with appropriate ballistic tables for the gravity, etc.).

A character who spends 200 hours in a given gravity increment, performing actions that involve athletic movement and judging ballistic trajectories may spend 1 CP to improve his or her DX modifier in that gravity by +1, to a maximum of -0. That activity may also count as training, on-the-job learning etc. as appropriate.


The modifiers to IN, HT, and FP for high gravity apply at 4.0 ms^-2 etc. above the gravity for which the character is anatomically and physiologically adapted by evolution, genegineering, or biomodification. It may be ameliorated by a G-suit etc.

[pnewman]

What about the notion that a species has evolved for the gravity of its home planet and should have lower problems adjusting to it, even if this individual has never experienced it before? I.e. humans evolved at 1.0 g. Therefore humans are genetically selected for the ability to operate at 1.0 g. Even if they've never experienced it before their genes are built for it.

Therefore shouldn't a human from Mars (0.38 native G, but only for the last two or three generations) be able to adapt to the Earths gravity much faster [i.e at a lower cost in hours or points] than a martian (native G 0.38 for millions of years) would? I suppose you'd probably give the human from Mars a higher strength than you would a Martian of the same mass, but that is just a small part of it.

[vicky_molokh]

Heavy-worlders with low-G experience are still mathematically more desirable than the other way around, due to the HT/IQ thing.

[Agemegos]

Originally Posted by vicky_molokh

Heavy-worlders with low-G experience are still mathematically more desirable than the other way around, due to the HT/IQ thing.

Then in a setting infested with Heavyworlders, impose an Unusual Background to compensate. If it's an advantage, it ought to cost points, right?

[vicky_molokh]

Originally Posted by Brett

Then in a setting infested with Heavyworlders, impose an Unusual Background to compensate. If it's an advantage, it ought to cost points, right?

Yeah, but figuring the price is problematic. I've got an idea, but I'm not sure if it's right:

the stats a character has are the stats as measured under Earth-Normal conditions. If a character's native gravity is one where those traits are penalized by (say) -4/-2 for normal humans, then the character must buy up those traits to the level at which they will provide acceptable result (in terms of encumbrance, stats etc.). Doesn't fix the BL silliness with low Gs, though. Any other bugs?

[lexington]

I think you lose one valuable thing be not basing it off the character's home gravity. Scalibility. A person from a high gravity world will be at a huge penalty in twice their native gravity while a person from a low gravity world will have no penalty in twice their native gravity.

[Agemegos]

Originally Posted by lexington

I think you lose one valuable thing be not basing it off the character's home gravity. Scalibility. A person from a high gravity world will be at a huge penalty in twice their native gravity while a person from a low gravity world will have no penalty in twice their native gravity.

I think that is correct, yes. The distance by which a ball comes in low or high is proportional to the absolute difference between gravity encountered and gravity expected, not the proportional difference. If the difference between 0.4 gee and 0.6 gee is that the ball is three inches lower than you expected and you don't catch it, then the difference between it you expect 1.4 gee it will take 1.6 gee to produce the same result, not 2.1 gee.

Furthermore I can't strictly be said to "lose" proportionality because the RAW don't have it either. Penalties by the RAW are based on absolute gravity difference in 0.2-gee increments, just as my suggested rules are.

[Anders]

And here I was looking forward to an article named Incorporating General Relativity into a GURPSian framework... :(

[lexington]

Originally Posted by Brett

I think that is correct, yes. The distance by which a ball comes in low or high is proportional to the absolute difference between gravity encountered and gravity expected, not the proportional difference. If the difference between 0.4 gee and 0.6 gee is that the ball is three inches lower than you expected and you don't catch it, then the difference between it you expect 1.4 gee it will take 1.6 gee to produce the same result, not 2.1 gee.

Furthermore I can't strictly be said to "lose" proportionality because the RAW don't have it either. Penalties by the RAW are based on absolute gravity difference in 0.2-gee increments, just as my suggested rules are.

Oh, you're right. Sorry about that. I was thinking their were increments of .2 of the person's home gravity.

[vicky_molokh]

Originally Posted by lexington

Oh, you're right. Sorry about that. I was thinking their were increments of .2 of the person's home gravity.

IIRC that's how Pressure behaves.