Stars of Classic Traveller

Rings by Axel-Astro-Art

Star system generation chapter from Classic Traveller Book 06: Scouts. Modernised and edited with annotations. Procedure has been simplified in order to streamline the exercise. Original values have been kept where possible.

Traveller notes two approaches to star system generation. The continuation approach follows the main world generation, creating a more detailed star system. The expanded approach is used to create a star system from scratch and choose a main world afterwards. Below I will present the continuation approach, so that you can proceed from where we left of in my previous post.

Generating a system is largely unnecessary to be able to run a game, but can be useful to flesh out a part of the sector where your crew spends a large amount of time. If you generate plenty of worlds in one star system, you can even run a small campaign set entirely within it.

Stellar Nature

Determine star characteristics, its orbits, gas giants and planetoids.

System Nature is determined by rolling 2d6. Results 2-7 is a solitary star, 8-11 are binary, and 12 is trinary. On referee’s decision a star system may be quadruple, with two widely separated binary systems.

Star Type is decided by rolling 2d6 on the table below. Roll + 4 if main world has POP 8+ or ATMO 4-9. Star types are given codes O, B, A, F, G, K or M. These letters indicate in descending order the temperature of the stars. (A mnemonic for remembering this sequence is Only Beings At Farpoint Get Klingon Massages”.) Spectral types O and B are extremely rare and will not normally be encountered. A referee may add no be more than one or two type O or B stars in a sector. Most likely making them centres of intrigue and mystery.

Roll 2 3-7 8 9 10-12
Type A M K G F

Real world fraction of main sequence stars: O is 0.00003%, B is 0.13%, A is 0.6%, F is 3%, G is 7.6%, K is 12.1%, M is 76.45%. The Sun is a type G star.

Star Size is determined by rolling 2d6 on the table below. Roll + 4 if main world has POP 8+ or ATMO 4-9. For star types K and M, size IV is instead size V. For B, A and F, size VI is instead size V.

Roll Size Description
2 Ia Bright supergiant
3 Ib Weak supergiant
4 II Bright giant
5 III Giant
6 IV Sub giant
7-10 V Main sequence (like our Sun)
11 VI Sub dwarfs
12 VII White dwarfs

Available Orbits: Roll 2d6 for number of available orbits around the star. Roll + 4 if star size III. Roll + 8 if star size la, lb, or II. Roll - 4 if star type M. Roll - 2 if star type K.

Zones: The orbits around a star are classified as unavailable, inner, habitable, and outer.

  • Unavailable orbits are subject to intense heat from the star. A planet in such an orbit would be converted to vapor and dissipated. Such orbits cannot be occupied by planets.
  • Inner zone orbits expose worlds to relatively large amounts of radiation, and such worlds are hot and inhospitable.
  • Habitable zone orbits are in a temperate region where stellar radiation is neither too much or too little. If other factors are right, life may exist on worlds in this region.
  • Outer zone orbits do not provide enough radiation for worlds, and they are cold and inhospitable.

Refence the primary star’s type and size. The number in the intersection indicates the habitable zone orbit number. The small number shows where the inner zone begins. Orbits before that are unavailable. Orbits after the habitable zone are outer system.

Type / Size Ia Ib II III IV V
B - Blue white ⁸13 ⁸13 ⁷12 ⁷12 ⁷12 ⁶12
A - White ⁷12 ⁵11 ³9 ⁰8 ¹7 ⁰7
F - Yellow white ⁶12 ⁵10 ²8 ⁰6 ⁰6 ⁰5
G - Yellow ⁷12 ⁴10 ²8 ⁰6 ⁰5 ⁰3
K - Light orange ⁷12 ⁵10 ²9 ⁰7 ⁰4 ⁰2
M - Orange red ⁷12 ⁶11 ⁴10 ¹8 ⁰0

Rolled separately.

Empty Orbits or Captured Planets are present if you roll 5+ on d6. Roll d3 for their quantity. Determine the specific orbits by rolling 2d6. For captured planets, determine the deviation by rolling 2d6 — 7, which shows the tenths digit of deviation. So if the total is -2 on orbit 5, the captured planet is situated at orbit 4.8 (5 — 0.2).

Gas Giants are present if you roll 9 or less on 2d6. Roll 2d6 for their quantity: 2-3 is 1, 4-5 is 2, 6-7 is 3, 8-10 is 4, 11+ is 5. The number present may not exceed the number of available orbits in the habitable and outer zones in the system.

Gas giants may be skimmed by spacecraft in order to refuel their tanks.

Planetoid belts are present if you roll 6 or less on 2d6. Roll 2d6 for their quantity, subtracting the number of gas giants: 0 is 3, 1-6 is 2, 7+ is 1. The number of planetoid belts in a system may not exceed the number of orbits remaining after gas giants are placed. For the purposes of distinction, an asteroid belt is used to describe a planetoid belt which is the main world in a system.

Placing Components

Gas giants, planetoid belts and the main world are placed in the system. Choose orbit randomly if multiple candidate orbits are available.

Gas Giants must be placed in available orbits in the habitable zone and in the outer system. While gas giants can be placed in inner orbits, they should not be placed starward of the habitable zone unless there are no other orbits available.

Planetoid Belts are placed in available orbits. If possible, planetoid belts should be placed in the next orbit inward from gas giants. For example, if a gas giant is in orbit number 8, then a preference should be made for placement of an asteroid belt in orbit 7.

Main World is placed in the habitable zone. If a gas giant is in that orbit, the main world will be a satellite of the gas giant. If the main world is an asteroid belt, then the belt may occupy any available orbit. If the main world has atmosphere 1 or lower, or more than A , then it is not required to be in the habitable zone.

Populating Orbits

Planetoid worlds are generated in a way similar to the main world, but various modifications are included for orbital position and other details. See the Worlds of Classic Traveller post for more details on what the results mean. Worlds are placed on all available orbits beginning from the closest to the star.

World Size (which are not gas giants or planetoids) are SIZE 2d6 - 2. If orbit 0, roll — 5. If orbit 1, roll — 4. If orbit 2, roll — 2. Orbiting a type M star, roll — 2. If the result is size less than 0, use S (for small world). If the world is a gas giant, determine its size by rolling d6. If 4+, the gas giant is small (SGG). Otherwise the gas giant is large (LGG).

Atmosphere is equal to 2d6 — 7 + SIZE. If the world is in the inner zone, roll — 2. If the world is in the outer zone, roll — 4. If SIZE less than 1, then ATMO is 0. If the world is at least two orbits beyond the habitable zone, roll 2d6 for 12 exactly: if successful, use ATMO type A instead.

Atmosphere codes 13-D (dense, high), 14-E (ellipsoid), and 15-F (thin, low) are added to the table. Dense atmosphere cannot support life at low altitudes, thin atmosphere is the opposite. For ellipsoid worlds, the atmosphere stays spherical, so the pressure varies greatly depending on where you are.

Hydrographies are determined by rolling 2d6 — 7 + SIZE. If inner zone, then 0. If outer zone, roll — 2. If size less than 1, then HYDRO is 0. If ATMO less than 1 or A+ , then roll — 4.

Population is 2d6 — 2. If inner zone, roll — 5. If outer zone, roll — 3. If not ATMO 0, 5, 6, or 8, then roll — 2. Population exceeding that of the main world is reduced to one less than main world POP.

Starports, spaceports, government, law level and tech level are added in a later chapter.

Satellite Generation

Determine the presence and quantity of satellites for worlds in the system. A result of 0 or less indicates no satellites. For the purposes of this system, satellites produced are at least 200 km in diameter.

  • For each planet (SIZE 1 or greater), the number of satellites is d6 — 3.
  • For small gas giants, the number of satellites is 2d6 — 4.
  • For large gas giants, the number of satellites is 2d6.

Satellite Size is determined by subtracting d6 from planetary size. If the planet is a large gas giant roll 2d6 — 4, if a small gas giant roll 2d6 — 6. If the result is size 0, create a ring instead. If the result is size less than 0, use S (for small world).

Satellite Orbits are determined by rolling 2d6: less than 8 is close, 8+ is far. If the planet is a gas giant, then 12+ is extreme distance.

Determine atmosphere, hydrographies and population as you would in the previous chapter.

Planetoid Society

For each planet and satellite determine its local government, law level, tech level and spaceport type.

Subordinate Government is determined by rolling d6. If main world government 6, then code 6. If main world government is 7+, then roll + 2. If there is no population, then government is code 0. Subordinate governments reflect the small, relatively powerless governments which can exist off the main world. Nevertheless, such subordinate governments may wield great power on their own territory.

Roll Code Government
1 0 No government
2 1 Company/Corporation
3 2 Participating Democracy
4 3 Self-Perpetuating Oligarchy
5+ 6 Captive Government

Subordinate Law Level is equal to d6 — 3 + main world LAW. GOV 0 means law level is 0.

Subordinate Facility presence is determined based on their requirements:

  • Farming world or satellite is in the habitable zone, has ATMO 4 to 9, HYDR 4 to 8, and POP 2 +. It supports agriculture and is exploited for farm products.
  • Mining world POP is 2+ and the main world is industrial. The world or satellite has recoverable ores and is being exploited for industrial reasons.
  • Colony world GOV is 6 and POP 5+. A settlement has been established on the world or satellite. A colony may represent any type of establishment, including a demonstration settlement, a penal colony, or simply a group intent on settling and exploiting new territory.
  • Research Laboratory is present if you roll 11+ on 2d6, roll + 2 if main world TECH is 10+. indicates that a scientific establishment has been located on the world or satellite. If the main world has TECH is less than 9 or has no population, then there is no laboratory. A research lab may be operated under the control of the government or private.
  • Military Base is present if you roll 12+ on 2d6, roll + 1 if main world POP is 8+, roll + 2 if ATMO equals main world ATMO. If no population, or if main world is poor, then no base is present. The military force is generally non-naval: it is an army or marine troop establishment.

Subordinate Tech Level is main world TECH - 1. However, it is equal to main world TECH if there is a military base or research laboratory present.

Spaceport type is determined by rolling d6. Roll + 2 if POP is 6+, roll - 2 if POP is less than 2. The major traffic centre in the system is the starport, all others are called spaceports.

Roll Type Description
1-2 Y No spaceport.
3 H Primitive facilities.
4-5 G Poor quality.
6 F Good quality.

Additional Details

Extra characteristics not covered in Book 03.


Naval Depot is a major naval support and training facility. Generally occupies an entire star system, displacing other development of its worlds. No more than one depot per sector.

Way Station is a large scout base involved in ship repair and maintenance, situated on an express ship route.

Travel Zones

Systems can be classified by their apparent danger to travellers.

  • Green/None: No particular danger or problem for travellers.
  • Amber: Caution advised for traveller; local conditions may pose some danger.
  • Red: Prohibited to travellers; local conditions can involve death or injury.

System Presence

You may use these rolls instead of the standard 4+ on d6 roll when determining world presence in a subsector.

  • Rift (density 4%): Roll 12 on 2d6 per hex.
  • Sparse (density 16%): Roll 6 on d6 per hex.
  • Scattered (density 33%): Roll 5+ on d6 per hex.
  • Standard (density 50%): Roll 4+ on d6 per hex.
  • Dense (density 66%): Roll 3+ on d6 per hex.

Communication Routes

Communication routes provide channels for information and trade, connecting important political and commercial centres. Communications routes are determined by the referee. Within Imperial space, they are jump 2 or 3.