Adapting 60 Years Worldgen for Classic Traveller

Via NASA

Part 1
Part 2

The absolute madman, he can’t keep getting away with it, etc etc.

This is a cobbled-together hackjob (as all good planet generation systems are) pulling from Classic Traveller, 60 Years in Space, Jon Zeigler’s CT adaptation of Architect of Worlds, the RTT Complicated Star System Generator, GURPS Space 4e, Perilous Void, and a couple odds and ends from Orion’s Arm. Mostly the first two.

So as to make sure that this remains semi-functional, I'm limiting it to temperate / goldilocks worlds for the time being, and I’m saving all the actual settlement generation for part 2.

Of course once Spacer comes out I'll have to rebuild this entire thing

Section 1: Sector Characteristics (Optional)

Since these steps will generate a good number of uninhabited systems for exploration, use normal CT placement and skip to Section 2 if you prefer standard mainworld density.

1.1 System Placement and Interesting Systems
Roll 1d6 for each hex; a solar system will be present on 4-6. On a roll of 6, the system is Interesting, and is guaranteed to be inhabited.

[“Interesting” in this context means that the system has things humans pay attention to; terrestrial planets, water, and stars that won’t instantly irradiate your progeny for seventy generations.]

There are 2d6+2 interesting systems per subsector; any 6s rolled beyond this number will have no special effect.

If you finish mapping the subsector and still have leftover interesting systems, roll 1d6 for each ordinary system and upgrade them on a result of 6 until all interesting systems are placed.

1.2: Other Inhabited Systems
When all interesting systems are placed, roll 1d6 for each ordinary solar system; the system will be inhabited on 4-6.

Optional: Mainworlds in boring-but-inhabited systems can be elided as space stations, if desired.

1.3: Interior, Frontier, and Empty Systems

• Interior systems are inhabited hexes with 2+ adjacent inhabited hexes.
• Frontier systems are inhabited hexes with 0 or 1 adjacent inhabited hexes.
• Empty systems are all uninhabited hexes; a d6 roll of 1-2 indicates an Outpost is present.

Set this aside for now, it will come back later in Part 2.

Section 2: System Characteristics

2.1 Stellar Multiplicity (2d6)

• 2-7: Singleton
• 8-11: Binary
• 12: Trinary

2.2 Star Type (1d6/2d6)
Roll 1d6 for primaries; add 1d6-1 to the primary roll for a secondary or tertiary. Subclass can be chosen randomly or ignored.

• 1: F
• 2-3: G
• 4-5: K
• 6+ M 

2.3 Star Age (3d6)

• F-Class - Young (3-7), Maturing (8-12), Mature (13-18)
• G-class - Young (3-6), Maturing (7-9), Mature (10-18)
• K & M-class-  Young (3-5), Maturing (6-8), Mature (9-12), Old (13-18) 

2.4 Gas Giants (2d6)
At least one gas giant will be present on a roll of 6+.

As a simplifying assumption, I’m not differentiating between gas and ice giants, since the only important feature is that they have enough hydrogen for easy refueling.

2.5 Gas Giant Arrangement (3d6)

• 3-10: Standard 
• 11-13: Eccentric
• 14-18: Epistellar

2.6 Debris belts (2d6)
A debris belt will be present on a roll of 8+, with two present on 12.

Section 3: Preliminary Characteristics

3.1 Temperature (2d6)
For the sake of expediency I’m cutting this step out for now and focusing purely on planets in the Temperate / Goldilocks band - I’ll add the other zones in later if I expand this further.

3.2 Special Orbits (1d6 + 2d6)
If a gas giant is present in the system and is not Epistellar, the mainworld has a special orbit on a 1D roll of 4+; roll 2D to determine special orbit.

• If 2D > Size, it is a moon of a gas giant
• If 2D = Size, it suffered a major collision after falling into a moon orbit: reduce its Size by 2.
• If 2D < Size, it either has a trojan orbit with a gas giant (odd) or a normal orbit (even)

3.3 Eccentricity and Axial Tilt (3d6)
The mainworld will be highly eccentric on a roll of 12+.

• DM +4 if gas giant is eccentric and mainworld temperature is Cool or warmer.
• DM -6 if standard gas giant arrangement.

If the first two (or two similarly colored) dice match, the planet has high axial tilt regardless of eccentricity.

If the mainworld is a moon, it will share temperature, eccentricity, and tilt with its primary: adjust them to match as needed.

3.4 Tidal Heating (2d6-2)
This step deals with moons changing temperature ranges, so it gets skipped for now.

Section 4: Mainworld Traits

4.1 Size (2d6-2)
Same as in CT, except Size 0 worlds should still roll for Atmosphere and Hydrosphere. Otherwise it ain’t broke and I ain’t fixing it.

4.2 Atmosphere (Size + 2d6 - 7)
Diverging from default Traveller, I’m operating with the presumption that most atmospheres are going to kill you and you should be masked and suited in all but the rarest special circumstances. Density remains the same, “breathable” is now just “standard” and represents the major components of an atmosphere for the given temperature band. For the temperate zone, these are:

• Trace: Carbon dioxide (1-3) or nitrogen (4-6)
• Standard: Roll 1d6;
• 1 - Nitrogen + oxygen
• 2-3 - Nitrogen + carbon dioxide
• 4-5 - Nitrogen + even more nitrogen
• 6 - Nitrogen + carbon monoxide
• Tainted: Atmospheres with an uncommon component. Roll 1d6, or pick an unlisted favorite.
• 1: Methane
• 2: Tholin compounds
• 3: Sulfur dioxide
• 4: Hydrogen sulfide
• 5: Ammonia
• 6: Nitrous oxide
• Exotic: Atmospheres that have retained a significant amount of primordial hydrogen; roll 1d6 twice, using (parenthetical) as the second result.
• 1: Methane (Hydrogen)
• 2: Carbon dioxide (Water vapor)
• 3: Carbon dioxide (Water vapor)
• 4: Ammonia (Water vapor)
• 5: Ammonia (No additional component)
• 6: Methane (No additional component)
• Corrosive: Extremely thick hothouse atmospheres dominated by carbon dioxide
• Insidious:  As Corrosive, with the addition of at least one strong acid as a major atmospheric component. Do not go here.

4.3 Hydrosphere (Atmo + 2d6 - 7)
Other temperature bands will have the chance for more exotic surface liquids, but for now it’s good ol’ H2O. Hydrate so you don’t diedrate.

4.4 World Type and Class (Derived)
World types are derived like trade codes, as below. Class I worlds have surface liquids, Class II worlds do not. Classes III and IV are limited to the outer system so they don’t apply here.

If eccentricity and tilt are not mentioned, they are not relevant for that world type.

Goldilocks World Types

• Atmo 0 + Hydro 0 = Airless II
• An airless ball of rock. Yay!
• Atmo ≥1 + Hydro 0 = Desiccated II
• With plate tectonics too weak to generate magnetic fields, any surface water previously present either boiled away or froze.
• Atmo 0-1 + Hydro ≥1 = Glacier II
• Any surface water has been locked in ice by a runaway cooling effect. If the process continues long enough, the atmosphere itself will freeze.
• Size 0 + Atmo ≥1 + Hydro ≥1 = Rift I
• Small worlds that lose most of their atmosphere before geological activity stops, preventing erosion from wearing down the geography. Water and atmosphere may remain at sheltered low-altitudes.
• Set Atmo and Hydro to 1.
• Atmo 2-9 + Hydro 1-3 = Desert I
• Planets with enough moisture to prevent a runaway greenhouse effect, but not enough to avoid lowered CO2 levels as atmospheric supplies are sequestered in sand.
• Atmo 2-9 + Hydro 4-9 + Lo-Ecc + Lo-Tilt = Craton I
• Planets with surface oceans, active tectonics, and a functioning carbon cycle. 
• Roll 1d6 for current phase of the continent cycle
• 1: Supercontinent breakup
• 2: Continent
• 3-5: Dry supercontinent
• 6: Island archipelagos
• Atmo 2-9 + Hydro 4-9 + Hi-ECC or binary+ system = Summer I
• Eccentric orbits lead to extreme seasonal temperature variation, where the planet will pass into and out of the habitable zone of its star.
• Roll 1d6 for subtype
• 1-3: Blue: Glacier worlds that thaw enough during the summer for surface water and an atmosphere.
• 4-6: Red: World-spanning glaciers during winter followed by extreme floodmelt in the spring and desiccation in the summer, with widespread fires if oxygen is present.
• Atmo 2-9 + Hydro 4-9 + Lo-ECC + Hi-Tilt = Shadow I
• Extreme temperature fluctuations due to length of day, either through spin-orbit resonance with the sun or high axial tilt.
• Roll 1d6 for subtype
• 1-2: Blue: Water freezes and glaciates on the night side.
• 3-4: Red: Dayside temperatures high enough for atmosphere to catch fire if oxygen is present.
• 5-6: Blue-Red: Both of the above.
• Atmo 2-9 + Hydro A = Ocean I
• The type where humans could conceivably go for a swim.
• Atmo A + Hydro 5-7 = Hot Water I
• High-temp, high-pressure worlds that are able to avoid runaway greenhouse effect through active geological and hydrological cycles.
• For purposes of determining life, these roll as Craton world.
• Atmo A + Hydro 8-9 = Steam II
• There’s technically no surface water left, but there is a suffocating, boiling atmosphere of mostly water vapor.
• Settlements must be aerostats.
• Atmo A + Hydro ≥ A = Ocean II
• As a Steam world, but with a heat-sterilized global ocean beneath and no real dividing line between.
• Settlements must be aerostats
• Atmo ≥ B = Hothouse II
• The archetypical venusian world: scorched rock and boiling clouds of high-pressure CO2.
• Set Hydro to 0
• Settlements must be aerostats.

Section 5. Astrobiology

5.1 Biochemistry
Since I’m sticking to Goldilocks worlds for this post, I’m presuming all mainworlds with life have some form of carbon-H2O biochemistry. Life is lazy, carbon is cheap, and exotic biochemistry is a ton of work for something best left for a focused exploration of an individual planet by the real sickos.

5.2 Life Sites (2d6)
The number of rolls for life is dependent on the mainworld size:

• Size 0-1: 1 site
• Size 2-3: d2 sites
• Size 4-6: d3 sites
• Size 7+: 1d6 sites

For Class I worlds, roll 2d6 for each site to see if any biomass is present (DM +1 if Size is 7+)

• 2-8: No biomass
• 9-B: 1d3 biomass
• C: 1d6 biomass
• D: 1d6+1 biomass

If any biomass is present on the world, oceanic sites will get a bonus of +1 biomass (representing life spreading to new environments), as follows:

• All sites on Ocean I worlds 
• 1-in-6 chance for sites on Summer I, Shadow I, and Craton I (Breakup or Continent)
• 2-in-6 chance for sites on Craton I (Supercontinent)
• 3-in-6 chance for sites on Craton I (Islands)

5.3 Biosphere Rating (Biomass + Xd6)
For each site with biomass, add the following to determine the biosphere rating of that site and the type of life found there:

• 1d6 if star is Young or Maturing
• 2d6 if star is Mature
• 3d6 if star is Old or Ancient

Life types are cumulative

• 2+: Single-celled life
• 4+: Photosynthesizers
• 7+: Eukaryotic life
• 9+: Multicellular organisms
• 11+: Skeletons
• 14+: Life spreads to all ocean sites
• 16+: Life spreads to all sites

If life spreads to a site, set its BR to the highest value on the world and reroll its biomass (keeping any higher result)

5.4 Oxygen Levels (Various)
Atmospheres with major components of hydrogen, ammonia, methane, CO2, or CO are reducing atmospheres (that is, any free oxygen in them gets tied up in other compounds).

• Free atmospheric oxygen (an oxidizing atmosphere) requires a BR of 12+
• Replace hydrogen with water vapor
• Replace ammonia with nitrogen
• Remove methane, CO2, CO as major atmospheric constituents
• Add biomass of all life Sites to determine % of oxygen

If the BR is 13, or if oxygen was rolled as a major component in step 4.2, add 1d6 x 10%, representing the lack of limiting factors.

If BR < 12:

• If BR is even, roll 1d6 for the gas exhaled by autotrophs in place of oxygen; add as a major atmospheric component.
• 1: CO2
• 2: Hydrogen chloride
• 3: Hydrogen peroxide
• 4: Methane
• 5: Hydrogen sulfide
• 6: Nitrogen

If BR is odd, autotrophs don’t produce enough oxygen for it to be a major component; if BR = 5 or 7, this is because a second autotroph species is absorbing it.

[The typical oxygen requirement for humans at 1 atmospheric pressure is 19.5-23.5% oxygen. Lower or higher than this range will result in mental and physical penalties, chance of permanent damage, and/or death.]

5.4 ET Intelligence (3d6)
Roll 3d6 for each site of BR 9+ for the most intelligent species present; with the following modifiers

• If result is higher than site BR, set to BR.
• -1 if atmospheric oxygen is 25%+; -1 for every 5% above that.
• -10 (all rolls)

A species with comparable intelligence to unmodified humans will be present on a roll of 6+. 

[The cut off here is abrupt because 60Y has a lot more in-depth stuff for ecosystem generation than most of the other systems I have on hand, so I can't really combine it with anything. This section really feels like it needs a redo.]

Putting it Together

Skipping Section 1.

2.1) Stellar multiplicity: Singleton (2d6 = 5) 
2.2) Star type: F (1d6 = 1)
2.3) Star age: Mature (3d6 = 13)
2.4) Gas giants: Present (2d6 = 9)
2.5) Gas giant arrangement: Standard (3d6 = 10)
2.6) Debris belts: Absent (2d6 = 6)
3.1) Temperature: Goldilocks / temperate 
3.2) Special orbit: N/A (1d6 = 3)
3.3) Eccentricity + axial tilt: No Ecc, No Tilt (3d6 - 6 = 9; 6 [6 3]
3.4) Tidal Heating: N/A
4.1) Size: 8 (2d6-2)
4.2) Atmosphere: Dense + tainted (Size + 2d6 - 7 = 9) 
    4.2a) Atmospheric components: Nitrogen (1d6 = 5) + methane (1d6 = 1)  
4.3) Hydrosphere: 9 (Atmo + 2d6 - 7 = 9)
4.4) World Type / Class: Craton 1 (Islands) (1d6 = 6)
5.1) Biochemistry: Carbon - H2O
5.2) Life sites / biomass: 2 sites (1d6 = 2); 
5.2a) Site 1 BM 3 (2d6 = 12; 1d6 = 3); Oceanic (1d6 = 6) +1 BM; Total 4
5.2b) Site 2 BM 0 (2d6 = 8); Terrestrial (1d6 = 3) 
5.3) Biosphere rating: 11, Skeletons (Site 1 BM + 2d6); No spread
5.4) ET intelligence: 1 (3d6 = 9, -10 hits minimum of 1)

So we've got an unbreathable pressure-cooker filled with alien fish that sticks to high heaven. The system is working.