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Imperial Interstellar Scout Service Details of the worlds of the Imperium (and beyond).

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Old August 13th, 2011, 04:49 PM
Chaos Chaos is offline
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Default Alternate Star System Generation Rules

Hi there! Iīve been away for some time, but here I am, once again, for now. :-)

Some of you may remember that I posted alternate and expanded star system generation rules I devised some years ago. By now Iīve come up with a new set of refined rules, somewhat more complex, but hopefully they make more sense, and give the Referee some more information to work with when fleshing things out.

Iīm posting these rules here because I would like some feedback from you guys about the rules... how much sense they make for you, any glaring scientific errors you spot, and so on. Of course, if you find yourself full of praise for my ideas, feel free to let me know about that as well... :-)


Anyway, letīs get started. Iīll post the rules in several portions, because thereīs quite a fews from the beginnings to the finished product.

Step 1: Stellar Configuration

Roll 2d6.

For a result of 2 to 8, the system is a solitary star.
For a result of 9 or 10, the system is a close binary.
For a result of 11 or 12, you have a close binary, and you roll 2d6 again for a second system component.
Repeat the process until you get a result of less than 11.

(For the purpose of these rules, a "close binary" is a binary system in which the smaller star occupies one of the larger starsī planetary orbitals. The different system components are further away from each other than the outermost theoretical orbital.)


Step 2: Spectral Types

Roll 2d6 for each star.

For a result of 2 to 8, the star is a Class M red dwarf.
For a result of 9 to 11, the star is a Class F, G or K main sequence star.
For a result of 12, the star is a Class O, B or A main sequence star.

(As other kinds of stars arenīt likely to be interesting for colonization or exploitation, the rules do not generate them randomly; actually I had considered excluding Class O/B/A entirely for that reason)

For Class F/G/K or O/B/A stars, roll 2d6 again to determine spectral type:

For a result of 2 or 3, the star is Class F or O.
For a result of 4 to 6, the star is Class G or B.
For a result of 7 to 12, the star is Class K or A.

For all stars, roll 1d10 (taking a result of 10 as 0) to determine subclass.

(Having one star in 432 be a Class O is unrealistic, but where would we be if nothing required the Referee to come up with an explanation? ;-))

Climate Modifier

The Climate Modifier of a Class G4 star is +0. For every subclass "above" or "below" that, the modifier increases or decreases by 2, up to +30 for A9 and -50 for M9; for every subclass above A9, the modifier increases by 5 up to +175 for O0.

(The Climate Modifier is one component determining worldsī climate)


Stars of different classes and subclasses also differ in their mass, which is used to determine their jump limit (which isnīt a fixed 100 diameter limit IMTU).


Step 3: Orbitals

(Iīm using fixed orbitals shells with radii approximating those observed in our solar system, at least for the inner nine shells (out to Neptune). I might introduce a more variable system of orbital radii later on, as that would complicate a lot of things)

For system components that are close binaries, roll 3d6 to determine the distance between the two stars.

Result 10 or 11: Orbital 0 (any mean distance significantly closer than the 60 million km radius of Orbital 1)
Result 9 or 12: Orbital 1
Result 8 or 13: Orbital 2
Result 7 or 14: Orbital 3
Result 6 or 15: Orbital 4
Result 5 or 16: Orbital 5
Result 4 or 17: Orbital 6
Result 3 or 18: Orbital 7

The smaller star occupies the indicated orbital of the larger star.
The next orbital outside that occupied by the smaller star is always empty.

When generating planets for a close binary pair, populate the inner half of the orbitals of both stars before populating the orbitals beyond the smaller star.
(For example, if the smaller star occupies Orbital 5 of the larger star, Orbital 6 is always empty, and both stars can have planets of their own in their respectively Orbitals 1 and 2, but both starsī orbitals 3 and 4 also remain empty. Orbitals 7 and beyond are a "common" planetary system shared by both stars.)

Stars also have a "safe" orbital, which is the innermost orbital in which the starīs size and gravitational influence allows planets to form.
Class O - Orbital 5
Class B - Orbital 3
Class A - Orbital 2
All other classes - Orbital 1
All orbitals inside this "safe orbital must remain empty regardless of all other considerations.


Each orbital has an Orbital Climate Modifier, also used to determine worldsī climate, which is simply the orbital number multiplied by -5.


Okay, thatīs the stars, in the next post weīll place planets and moons and the like. Iīm looking forward to your feedback.
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