Alternate Star System Generation Rules

[Chaos]

Hi!

For me, the rules for star system generation as presented in the T20 THB (the only Traveller ruleset with world generation rules that I own) are, to put it bluntly, unsatisfactory. The rules for generating the star and any other worlds, planetoid belts and gas giants are more or less an afterthought to the creation of the mainworld; that is probably intentional, since the "action" in a star system is probably centered around the mainworld, but in a universe were space travel is so commonplace, I would expect the other bodies of a solar system to be settled, or at least exploited, to a significant degree.

For that reason, I have thought up alternative rules for generating star systems, taking a different approach.

(for ease of reference I am splitting this up into three posts; system generation, world generation, and colony generation)

Since IMHO the focus of interstellar colonization will be on systems which may contain habitable planets, my star generation rule generates only such stars:

Roll 1d6 for spectral class;
1 class F
2-3 class G
4-5 class K
6 class M
Then roll 1d10-1 for subclass (0-9); for class M stars, roll 1d6-1 only

The orbital radii given in the THB are for a G2 star; for less luminous stars, subtract 3% per subclass (i.e. -3% for G3, -6% for G4 etc., to -69% for M5); for more luminous stars, add 3% per subclass.

The innermost orbit occupied is determined by rolling 1d6/3, i.e.
1-2 orbit 0
3-5 orbit 1
6 orbit 2
The outermost orbit occupied is determined by rolling 2d6. Every orbit from the innermost to the outermost orbit is occupied by *something*.

For each such orbit, roll 1d6.
1-3 solid planet
4 planetoid belt
5 small gas giant
6 large gas giant
Sort the results, with the solid planets occupying the inner orbits, gas giants in the outer orbits, and asteroid belts in between.

The habitable zone in centered on a distance of 25 million kilometers plus 5 million km per spectral subclass above M5 (i.e. 30 million km for M4, 35 million km for M3 etc, giving us 140 million km for a G2 star such as Sol. The habitable zone extends 25% of that distance inward and outward, i.e. from 105 to 175 million km for a G2 star.

 

[Chaos]

So now we have anywhere from 1 to 12 planets.

Asteroid belts and gas giants don´t get much detail.

For asteroid belts, roll 2d6 to determine density; an asteroid belt contains about the mass of a planet with the same size digit as the belt´s density - which would, IIRC, make our belt here in the solar system a density 7 or 8 belt

For gas giants, roll 2d6 to determine size; for small gas giants, size digit time 8,000 is the diameter, for large gas giants it is size digit times 24,000.
Also, roll 2d6 twice for small and three times for large gas giants.
2-7 no moons
8-9 1 moon
10-11 2 moons
12 3 moons
The sum of the result determines the number of larger moons the gas giant has - "larger" meaning UWP size digit 1 or bigger, or roughly 800+ km. Okay, Jupiter and Saturn have dozens of moons each, but most of those are tiny anyway.

For solid planets, things are a little more complicated.
First you roll 2d6 once for moons, as with gas giants.

The you determine size, but with 2d6, not the 2d6-2 as we´re accustomed to. This gives us a minimum planet size of 2,400 km, which all planets in our solar system except Pluto exceed, and it´s not too clear if Pluto actually is a genuine planet or a runaway moon.
BTW, planet sizes 11 and 12 are denoted B and C as usual with Traveller.

Then you roll for atmospheric density as you normally would for atmosphere; the modifiers are -2 for inner or outer zone. I saw no reason why outer zone should get a -4 modifier when the inner zone gets only -2
0 vacuum
1 trace
2-3 very thin
4-5 thin
6-8 standard
9-10 dense
11-12 very dense
13+ too dense for humans
This is not the UWP atmosphere digit, yet, though.

Hydrographics is determined as usual, with all the modifiers in the THB, except of course we don´t have 0, 1 or S sizes in this ruleset

The next step is climate. Roll 2d6-7+atmospheric density-hydrographics. Add +3 for each orbit away from the habitable zone in the inner zone, subtract -2 for each orbit away from the habitable zone in the outer zone.
<-6 too cold
-5 to -4 cold
-3 to -1 cool
0 Earth standard
1 to 3 warm
4 to 5 hot
6+ too hot
In my trial runs, I´ve seen climate values from -20 to +20 for some worlds

The next step is determining the complexity of native life forms.
Roll 2d6 and apply the following modifiers:
Atmosphere 0 or 1: -4
Atmosphere 2 or 3: -2
Atmosphere 11 or 12: -2
Atmosphere 13+: -4
Hydrographics 0: -4
Climate <-8: -6
Climate -7 or -6: -4
Climate -5 or -4: -2
Climate 4 or 5: -2
Climate 6 or 7: -4
Climate 8+: -6
The results have the following meaning:
0: no life forms
1-2: microscopic life, probably in the oceans
3-4: macroscopic life in the oceans
5-6: plant life on land, maybe some animals
7-8: complex animal life on land - e.g. Earth at the time of the dinosaurs
9-10: highly complex ecosystems - e.g. during the reign of mammal megafauna
11: ecosystem includes sentient or proto-sentient life
12: indigenous civilization, i.e. TL 0 or above

The last mandatory step of planet creation is determining the atmospheric composition. Roll 2d6 and modify according to native life:
Complexity 0-4: -4
Complexity 5-6: no modifier
Complexity 7-8: +2
Complexity 9+: +3
The result has the following meaning:
-1 or less, or a natural 2: corrosive
-1 or less, AND a natural 2: insidious
0 to 5: toxic
6 to 8: marginal
9 to 10: sub-optimal
11+: optimal


As optional steps, those who like this kind of thing to bring more variety to their planets can vary the planetary diameter, by modifying the standard diameter by rolling 2d6-7 * 150 km, or 6d6-21 * 50 km, whichever they prefer.
Similarly, they can vary planetary gravity; either multiply the standard gravity by 2d6*10% or 4d6*5% - most planets in our solar system have a lower density and thus lower gravity for their diameter than Earth does -, or - if you like it precise - by dividing the planetary diameter by 12,750 - Earth´s diameter - and multiplying the result by 2d6*10% or 4d6*5%.
In my trial runs, I´ve had planets with 0.04 to 1.85 g

I know that my two-step atmosphere generation is hard to translate into a UWP code in some cases; I´m working on that.

Dang, I just noticed it´s already past midnight. I´ll post the colony generation thing tomorrow.

 

[Pickles]

Are you aware of Malentfant's Stellar Generation Rules? They are quite popular among CT sector-builders.

 

[Chaos]

Originally posted by Bromgrev:
Are you aware of Malentfant's Stellar Generation Rules? They are quite popular among CT sector-builders.

I read them a while ago, and just re-read them. Thanks for reminding me.

Malenfant´s approach, like the THB approach, is from the mainworld to the starsystem, while mine is the other way around.
Also, while traditional Traveller places colonies on all kinds of planets (remember that the Population scores are not modified in any way by planetary environment), I prefer to think that real colonies, i.e. places to live, not just places to work, are located on habitable worlds only.

On the other hand, one could, very well, replace my very simplistic star generation process with Malenfant´s procedure for generating the star of a habitable/hi-pop mainworld. It looks like more work, but then, my generation rules as a whole are already so much more work than standard world generation, it doesn´t make a difference.

***


Also, I noticed that I forgot about two things last night - it was fairly late, and I was tired.

First, moons. A moon´s diameter is 2d6*5% that of the planet it orbits. Determine which size digit this diameter corresponds to, and then proceed normally with world generation.

Second, habitability.
A world is habitable for humans if it has optimal, suboptimal or marginal atmospheric composition, atmospheric density of 2 to 12, and a climate of -5 to 5.
From the planetary conditions, a habitability code is determined. You start from ideal conditions (optimal atmosphere, density 7, climate 0, gravity 1.00 g) and add up the deviation from this ideal:
Suboptimal atmosphere: 1 deviation
Marginal atmosphere: 3 deviations (not cumulative with suboptimal)
Atmosphere 9-10: 1 deviation
Atmosphere 11-12: 2 deviations
Atmosphere 4-5: 1 deviation
Atmosphere 2-3: 2 deviations
Climate -4 or 4: 1 deviation
Climate -5 or 5: 2 deviations
Gravity .51 to .75: 1 deviation
Gravity .26 to .50: 2 deviations
Gravity .25 or less: 3 deviations
Gravity 1.25 to 1.49: 1 deviation
Gravity 1.50 to 1.74: 2 deviations
Gravity 1.75 or higher: 3 deviations

Result:
No deviation: class A1
1 deviation: class A2
2 deviations: class A3
3 deviations: class B1
4 deviations: class B2
5 deviations: class B3
6 deviations: class B4
7 or more deviations: class B5

A-type worlds are terra-norm worlds (Earth itself has slipped into class A2 IMTU from atmospheric pollution); B-type worlds are habitable but probably not very comfortable for immigrants - those who are born there probably do feel comfortable on most of them.

From my test runs, A1 type worlds are VERY rare; I´ve had 1 out of maybe 100 or so habitable worlds. However, maybe 1 in 3 or so habitable worlds are A2 or A3.

 

[Pickles]

I can see a PDF coming on ... go on, you know it makes sense ...

 

[Chaos]

All right, now for the 3rd part: colony generation.

First off, I´ll admit that this part isn´t as clear-cut as the rest and involves a lot of arbitrary referee decisions. This is mostly because the purely random results I´ve seen are often not plausible to me, to say the least.


Rather than simply roll up the UWP population codes, you first decide what kinds of habitation there is on the various planets and moons. This is, of course, highly subjective and depends both on the TU in question and the location of the system (core or frontier sector). I´m using my own TU as the basis of the following suggestions.

Colonies
I think it is reasonable to assume that all A-type and most B-type planets (at least the better B-type, such as B1 and B2) have been colonized and are sporting a population of several million to several billion people. Exceptions to this are systems near the edge of colonized space, where only the best planets have been fully colonized, if at all.
Personally, I assume a population code of 1d4+6 for A-type planets and 1d6+3 for B-type planets. Government codes are then generated normally.

Mining outposts
BTW, by "outpost" I refer to any closed environment installation, like an orbital station, a dome (arcology) or subterranean installation. "Open" settlements are "colonies" IMTU. And there is no reason why a planet couldn´t have two or more kinds of outposts, separately or combined into one outpost.
Mining outposts can probably be found in the asteroid belts, and on some uninhabitable worlds, preferably low-gravity, trace or vacuum worlds.
Mining outposts usually have population code of 1d4+1.

Harvesting outposts
"Harvesting" refers to the practice of gathering some of the products of a planet´s or moon´s ecosystem, maybe in the form of pharmaceuticals or drugs, or furs and pelts, or even photo safaris in some cases. This, of course, is only feasible if the planet has native life, the more complex, the more probable is the presence of a harvesting outpost - roll 2d6-2; if the result is less than the Native Life code, then a harvesting outpost is feasible.
Here, too, I assume a population code of 1d4+1.

Research outposts
Research outposts can exist for many reasons. One is the presence of native life, especially of a complexity of 5 or higher, on an uninhabitable world - or any life at all on a vacuum or trace atmosphere world.
Then, of course, there is the idea to keep research away from prying eyes; any planet that doesn´t have a corrosive or insidious atmosphere could house such a research outpost, especially if it is a moon of an inhabited planet.
Here I suggest a roll of 1d6:
1: Population code 1
2-4: Population code 2
5-6: Population code 3

Military outposts
IMTU, Naval bases are rarely on inhabited planets, except for the purely administrative parts, recruitment, training facilities and such; the depots, repair facilities, command facilities and so on are, whereever feasible, located on a moon, so as to keep potential spies watching from merchants ships as far away as possible from these bases.
The presence or absence of a Naval base is determined as described in the THB, except only one roll per planet/moon system is made, for the best starport present. Roll 1d6 for population code:
1: Population code 2
2-4: Population code 3
5-6: Population code 4
Add 1 to the code if the base is a subsector HQ, add 2 for a sector HQ.

Scout bases use the same procedure, except the roll is made for the starport that offers the best chance of having a scout base. Subtract 1 from the population code.

Army and Marine bases are usually located on inhabited planet, although the Marine Corps has a few bases on uninhabitable planets, to serve as training facilities to prepare Marines for fightin in that kind of environment. Treat as a Naval base for population code.

Most inhabited systems, especially along borders, have sensor arrays installed on one planet or moon, usually a vacuum world; these are usually sensors with a System-Wide range.
Roll 1d6 for population:
1-4: Population code 1
5-6: Population code 2

Terraforming
Uninhabitable planets, especially those with a breathable atmosphere that are uninhabitable due to atmospheric density or climate, can be subject to terraforming procedures. In that case, a terraforming outpost will be located on the planet.
Roll 1d6 for population:
1-4: Population code 1
5-6: Population code 2

Prison facilities
Some uninhabitable worlds have prison facilities, to make it even harder for inmates to escape and survive.
The population code is 1d4+1.

***

Government codes
For most colonies, government codes can be generated normally; very young colonies, on the other hand, could be assigned goverment code 6 (captive government) manually, unless they are an independent colonization project.

For mining, harvesting and research outposts, I use the following method to assign a government codes:
Roll 1d6:
1-2: government code 1
3: government code 3 for mining outposts (i.e. Belter community), 1 for others
4: government code 5
5: government code 9
6: government code 6, or roll normally

Military outposts can all be considered to have government code 9, as they´re being administered by the military bureaucracy.
Prison facilities all have government code 6.
Terraforming facilites have a 50/50 chance of having government codes 1 or 5.


Law Levels
By and large I have kept law level generation, except one big exception:
All worlds with government type 6 that are not very young colonies are supposed to be under martial law, military occupation, or some similar condition; law level is determined by adding 2d6+2 to the government code, i.e. law level is 2d6+8, or A to L. It simply makes sense to abolish private ownerships of weapon on such worlds.

Starport
Starport type is determined as usual, except that all rolls for each planet/moons system are made, modifiers are applied, and then all results except for the best are modified by +2 - i.e. all starports except for the best are a bit smaller than they would be. This +2 modifier cannot change an E starport into an X starport.

Also, there is a minimum population for starports:

For type A, population code 7+, or a Naval base
For type B, population code 6+, or a Naval base
For type C, population code 5+
For type D, population code 3+
For type E, population code 1+

Tech Level
Tech level is determined as usual, with the exception that there is a minimum TL for most planets.
IMTU, all habitable planets (except for those with native, i.e. non-human (IMTU there were no Ancients that seeded humans all over space) civilizations, have a minimum TL of 4.
Worlds with exotic atmosphere have a minimum TL of 6.
Vacuum or trace atmosphere worlds have a minimum TL of 8.
Outposts in asteroid belts or those involving orbital stations must have a TL of 9 or higher.


This is it. At least I think it is. I have probably forgotten a thing or two.

Any comments so far?

 

[Plankowner]

I like you system, it seems well thought out. BUT (there's always a but ) I have one little nit...

One of the great things about traveller was having to explain away some of the truly bizarre combinations of characterists in the UWP. Sure, you could just change the ones that seemed really wrong, but where is the fun in that? I always try to make sure that somewhere in my generation systems there is a "roll on the random table".

For example, IMTU I use a modified population roll that is 1d6+DMs. The DMs are mostly based on the type of atmosphere. BUT, if you roll a 6, you use the standard 2d6-2 population roll. This makes it possible to have a real garbage world with a Population A that as the GM I now have to explain. I LIKE having to do that, at least some times, it makes the universe surprising. If every A1 type world has the same basic population, it can get a little boring. WHY is that A1 planet, right in the middle of the Core Sub-Sector not inhabited? Leads to good roll-playing if you do it right.

 

[Chaos]

Originally posted by Plankowner:
I like you system, it seems well thought out. BUT (there's always a but ) I have one little nit...

One of the great things about traveller was having to explain away some of the truly bizarre combinations of characterists in the UWP. Sure, you could just change the ones that seemed really wrong, but where is the fun in that? I always try to make sure that somewhere in my generation systems there is a "roll on the random table".

For example, IMTU I use a modified population roll that is 1d6+DMs. The DMs are mostly based on the type of atmosphere. BUT, if you roll a 6, you use the standard 2d6-2 population roll. This makes it possible to have a real garbage world with a Population A that as the GM I now have to explain. I LIKE having to do that, at least some times, it makes the universe surprising. If every A1 type world has the same basic population, it can get a little boring. WHY is that A1 planet, right in the middle of the Core Sub-Sector not inhabited? Leads to good roll-playing if you do it right.

You have a point there... however, in my recollection about half the world generation but straight-from-the-book random generation need to be explained.

I mean, why IS that A1 planet in the Core Sub-Sector not inhabited? Especially if there is a Pop A asteroid belt 1 parsec away... and a Pop 9 world with insidious atmosphere and Hydrographics A is 2 parsecs off the other way? Are people so fonding of taking a bath in sulphuric acid, or hopping from asteroid to asteroid, that they don´t even think of moving to that paradise that´s virtually next door?

With standard generation, about 3 out of 4 perfectly inviting habitable worlds have less, sometimes far less, than my minimum population of 10 million people. 3 OUT OF 4, for crying out loud! While 1 in 12 of the most hostile, barren and bleak heaps of rock are crammed to the bulkheads with billions of people!

Your system isn´t bad, either. I assume you´re talking about mainworlds only, so it makes sense that all worlds are inhabited at least to some degree. Me, I usually have 5-15 worlds (planets and moons) per system, I can pick and choose.

One other thing I´ve experimented with, before I came up with my current rule system, is generate a batch of, say, between 20 and 50 mainworlds - 1 or 2 subsectors at a time - and then roll up the requisite number of population scores, sort the mainworlds by habitability, and then assign highest population scores to most habitable worlds. As long as you keep the number of worlds neither too large nor too small, you´ll end up with a good number of reasonable result and a few that need explanation.

I had two reasons to come up with my system. One, I had been working on something like this for a homegrown SF RPG before I found Traveller, and Two, I wanted star systems that are more than just mainworld plus appendix.

 

[Plankowner]

I agree with the wanting more than a MW + Appendix. I had a friend that ran a game where everything took place in one star system. Two stars about 50 AU apart with just about every planet/moon with someone on it. Very like what Firefly turned into, but we used the regular traveller stuff without Jumps. As I remember, we eventually found an derelect Scout Ship and we found out that we were a lost colony at the edge of the Imperium!

The amount of detail that the GM came up with was truly amazing. There were multiple governments, mega corps, pirates, Space Gypsys everthing, all in one system and it didn't feel confining or crowded. I wish more systems could be detailed that way. As a GM, I almost never had the time to get that level of detail. I just made it up as I went. Some times it worked, some times it didn't.

 

[Chaos]

Originally posted by Plankowner:
I agree with the wanting more than a MW + Appendix. I had a friend that ran a game where everything took place in one star system. Two stars about 50 AU apart with just about every planet/moon with someone on it. Very like what Firefly turned into, but we used the regular traveller stuff without Jumps. As I remember, we eventually found an derelect Scout Ship and we found out that we were a lost colony at the edge of the Imperium!

The amount of detail that the GM came up with was truly amazing. There were multiple governments, mega corps, pirates, Space Gypsys everthing, all in one system and it didn't feel confining or crowded. I wish more systems could be detailed that way. As a GM, I almost never had the time to get that level of detail. I just made it up as I went. Some times it worked, some times it didn't.

This is absolutely awesome; it is also exactly the kind of thing that I hope my system generation rules will enable.