Some Advanced GURPS Space Moon Generation Rules

[Agemegos]

Originally Posted by AMKTheSpook

I fixed these issues with an updated Gas Giant Arrangement Table (page 107 of GURPS Space):

3D6 Roll ----- Gas Giant Arrangement
3 to 4 ----- No Gas Giant
5 to 14 ----- Conventional Gas Giant
15 to 16 ----- Eccentric Gas Giant
17 to 18 ----- Epistellar Gas Giant

The publicly-available version of my spreadsheet is faithful to the rules as written, but the version I use to generate my own universe has (among other changes) a modification to that table that is even more extreme:

Gas giant arrangement table

p.107

3d6
3 none
4–15 conventional
16 eccentric
17–18 epistellar

Agreed here also. My Quick N Dirty Fix (Trademark) was simply to multiply all the values in the Planetary Orbital Eccentricity Table (GURPS Space page 118) by 10.

Multiply? The problem is that they are large. And an eccentricity of 1 or larger defines an open, non-repeating (parabolic or hyperbolic) orbit. I use the following in my private model:

Planetary orbit eccentricity table

p.116

3d6 (modified)
-3 – 3 0
4 – 5 0.01
7 – 9 0.02
10 – 11 0.03
12 0.04
13 0.08
14 0.15
15 0.2
16 0.35
17 0.5
18 0.75

Also agreed. My fix was simply to recompute the blackbody temperature of the planet at the aphelion and perhelion values of its orbit and use the resulting value on the World Type Assignment Table (GURPS Space page 115) as the World Type for those positions, similar to the way the planet Ploor was supposed to have shifted World Type in the Lensman books, or the way the planet in Fire Time by Hal Clement did.

I calculate both and display them on the planet information sheet, but I hadn't gone as far as re-calculating the world type: I ought.

Note that world type ought to be determined by the perihelion temperature and MMWR. Molecules that boil off in Jeans Escape at perihelion won't come back at aphelion.

So nice to find a knowledgeable GURPS person who agrees with my ideas...:)

I'm not actually very knowledgeable about GURPS, and I'm only an amateur at planetary science.

[AMKTheSpook]

Originally Posted by Agemegos

The publicly-available version of my spreadsheet is faithful to the rules as written, but the version I use to generate my own universe has (among other changes) a modification to that table that is even more extreme:

Gas giant arrangement table

p.107

3d6
3 none
4–15 conventional
16 eccentric
17–18 epistellar

Very nice. I shall steal it forthwith for the next version of my software...

Originally Posted by Agemegos

Multiply? The problem is that they are large. And an eccentricity of 1 or larger defines an open, non-repeating (parabolic or hyperbolic) orbit. I use the following in my private model:

Planetary orbit eccentricity table

p.116

3d6 (modified)
-3 – 3 0
4 – 5 0.01
7 – 9 0.02
10 – 11 0.03
12 0.04
13 0.08
14 0.15
15 0.2
16 0.35
17 0.5
18 0.75

Actually you saw the buggy post; I meant the multipler to be 0.25 (ie divide by 4) but something distracted me (of a feline nature attempting to catch and eat my mouse...)

Again, I pay the ultimate compliment and "borrow" your table again... :)

Originally Posted by Agemegos

I calculate both and display them on the planet information sheet, but I hadn't gone as far as re-calculating the world type: I ought.

Note that world type ought to be determined by the perihelion temperature and MMWR. Molecules that boil off in Jeans Escape at perihelion won't come back at aphelion.


I'm not actually very knowledgeable about GURPS, and I'm only an amateur at planetary science.

I factor that into the atmosphere calculation routines, yes, especially for hydrogen and helium. Although the "hot jupiters" of the exoplanet researchers are giving us cause to rethink some of those assumptions.

You are good enough to create a really impressive universe in your "Flat Black" setting! I've been browsing it in my spare time and intend to "borrow" a number of elements for my own work, ahem...

royce