Planets, gravity, G-experience, G-tolerance, and Free Fall skill

[Agemegos]

A GURPS character has a "home gravity" (B.17). within ±0.2 gees or this home gravity he or she acts as normal. For each full 0.2 gees difference between the prevailing gravity and a character's home gravity, a character suffers a -1 ro all DX rolls and DX-based skills. There is also a penalty to IQ and HT for gravity well above home gravity, but it comes in at larger values (B.350) so we don't have to worry about it for the purposes of this discussion.

A character can improve his or her performance in non-home gravities by one skill or by either of two advantages.

The skill is Free Fall (B.197), "the ability to operate in a free-fall (zero-gravity) environment." When you are in free fall you roll against the lower of this skill and your DX or DX-based skill for DX-based tasks. I presume that that means DX and skill without the penalty for non-home gravity, because it is hard to get rid of that penalty as we shall see below. If the penalty does apply everyone is going to be pretty clumsy in free fall, and stay that way despite acquiring Free Fall skill. (Note that there are rules for free fall conditions in the Free Fall skill description that do not appear in the rules section on 'Different Gravity' (B.350).

The first advantage (taken alphabetically) is G-Experience (B.57). This advantage costs 1 point per gravity "field" (the example making it clear that this means "value of local gravity"), and halves the DX penalty for operating in this "field". I am not sure of the rule for rounding fractional skill penalties (B.9 doesn't mention skill bonuses or penalties), but I am going to assume that you round up, that -½ becomes -0. The rules don't say how wide the band of gravities encompassed by a "field" is. I presume that the difference betyween 0.16 gee and 0.161 gee wouldn't matter to anything except a sensitive gravitometer, but I couldn't say whether the "field" encompassed ±0.2 gee (like a home gravity) or one of the 0.2-gee increments based on home gravity (so that a person from Earth with G-experience in the Moon's gravity would suffer halved penalties (-2 instead of -4) in the increment 0 gee to 0.2 gee), or what.

You can buy G-Experience in all gravities (ie. halve all DX penalties but not IQ or HT penalties) for 10 points.

Note that G-experience will never allow you to fully acclimatise to 0.5 gee if you grew up at 1.0 gee, etc.

The other useful advantage is Improved G-Tolerance. This widens the "G increments" around home gravity. For 5 character points you have no penalties in the range within home gravity ± 0.3 gees, and -1 per full 0.3 gees away from your home gravity. For 10 points you get -1 per full 0.5 gees, which is better than G-Experience in all gravities at the same price, and also reduces the HT and IQ penalties at very high gravities. For 15 points you get -1 per full 1.0 gees away from home; for 20 you get -1 per full 5 gees difference; and for 25 you get -1 per full 10 gees difference.

Unfortunately Improved G-Tolerance is not a learnable advantage. You can't buy it to represent acclimatising to a new planet's gravity.

As we saw a while ago, in a universe compliant with GURPS Space shirtsleeve-habitable planets will have surface gravities ranging from about 0.44 gee to 1.44 gee, none lower, and few higher (those not at all common and not very appealing). The average surface gravity of habitable planets will be about 0.8 gee.

Typical characters will have a home gravity of about 0.8 gee. They will suffer no DX penalty in the range approximately 0.6 gee to 1.0 gee. They will have a -1 from 0.4 to 0.6 gee, and from 1.0 gee to 1.2 gee which they can buy off for 1 point per "gravity field"—but we don't know how wide gravity fields are. They will have a -2 at 0.2 gee to 0.4 gee (encompassing no habitable worlds, but pertaining at some outposts and perhaps on some spaceships) and from 1.2 to 1.4 gee (including some habitable worlds and high-spec spaceships), which they will be able to reduce, but never completely eliminate. They will have a -3 in microgravity to 0.2 gee and on some, not very appealing, habitable worlds.

A player will be disadvantaging his character in a way that is hard to mend if he or she makes him come from a planet with a surface gravity much below 0.8 gee or much above 0.9 gee, because there are going to be plenty of inhabited worlds with gravities only a little above 0.5 gee or only a little below 1.2 gee.