Star System Hex Map Generation for Classic Traveller

11 Oct, 2026

Meant for use with this sort of spaceship movement

A star system is mapped on at three scales, represented by three 13-across hexagonal maps. The first contains hexes which are 10-million kilometres across, the second hexes 100-million kilometres across, and the third hexes 500-million kilometres across¹ . These are referred to, respectively, as the "10M", "100M", and "500M" maps. These hexes are used for the placement of celestial bodies and for interplanetary travel, detection, and combat. Each smaller map is in the central hex of the larger. The placement of moons and near planet features, and tactical space combat, uses 100,000 kilometre hexes ("100k" maps). Generating these can be deferred until necessary.

Begin by rolling d66 and consulting the System Centre Table: This provides stellar classification and results of "m" indicate multistellar system: Randomly select from the rows cells below to determine its stellar companion. Randomize the size of each star by rolling 1D x 5%. This affects jump limits, but not system or habitable zone limits.
Reference the Star Data Table and plot the system inner limit (within which planets are not found), habitable zone, frost line, and outer limit (beyond which planets are not found). When placing astronomical objects, Reroll results within or beyond the inner or outer limits. The range given for the inner limit is the outermost hex in which planets cannot be placed. Hab zone inner and outer limits are inclusive. The frost line range given is the innermost hex in which the frost line table is rolled at, and the system outer limit is the innermost hex in which planets cannot be placed.

By default each system contains up to 6 points of interest: Roll 6D: Each result of 1-2 is placed on the 10M map, 3-4 on the 100M map, and 5-6 on the 500M map. Number the faces of the central hex 1-6. Roll each astronomical object die twice: The first result is the face of the central hex it is nearest to, the second is the range in hexes from the central hex. (For example, if the rightmost hex face was "2", then rolling 2, 5 for an astronomical object would see it placed five hexes to the right of the central hex).

Note the zone in which each astronomical object falls. Roll 2D and consult the appropriate column of the Astronomical Object Table. Some results will require you to roll for the number of moons, in which case roll 2D+MoonModifer and consult the Moon Number Table. Place moons on 100k maps according to taste or using 1+(2D keep lowest) hexes from the planet or next inner moon orbit. Roll 1D for each moon and consult the Moon Size table; The moons of terrestrial planets are scaled according to their planet, those for gas planets are given directly. Consider noting the L1-L5 Lagrange points as space infrastructure is typically placed there² . Note the 100D jump limit imposed by the central star. If desired, add Space Infrastructure and plot sensor detection limits.

Flavour results appropriately for their stellar distance. E.g. Epistellar terrestrial planets are perhaps lava worlds or chthonian planets, and are very likely to be tidally locked; Worlds in the sunward hexes of the habitable zone are hotter than may be comfortable - perhaps tidally locked eyeball worlds; terrestrial planets beyond the habitable zone are icy. And so on, and so forth. I recommend you look at Dan's world generator if more detail is desired.

Eccentricity of worlds is according to the discretion of the DM: Consider rolling twice for map scale and stellar distance, taking the closer result to be the periapsis and the farther to be the apoapsis.

The main world of a system may be placed or selected during any step. Note that worlds placed within the 100D limit of a star are more onerous for Travellers to reach; This may stunt the economy and therfore starport type. It may also be desirable for reasons of defence.

For most stars, on the scale of days or weeks only epistellar planets could move appreciably. I would recommend not bothering with planetary orbits (or, indeed, lunar orbits) unless it's of importance. Note that objects orbiting stars of larger mass orbit faster than those at the same distance orbiting smaller bodies.

Star System Creation Checklist

1. Roll d66 on System Centre Table and randomize star size. If multistellar, roll again from below cells
2. Plot inner limit, hab zone inner limit, hab zone outer limit, frost line, system outer limit, and stellar 100D jump limit
3. For each astronomical object: Roll for map placement, bearing from star, and distance from star
4. For each astronomical object, roll 2D for type. Roll for size if necessary.
5. Roll for moon presence, size, and placement
6. Place or select main world and generate attributes
7. Roll for and place Space Infrastructure
8. Plot sensor limits
   
   Tables
   
   

• RP: Rogue Planet
• BH: Black Hole
• L/T/Y: Brown dwarf, randomly determine type
  
  

In parenthesis is the Moon Modifier

• MrBdy (no moons) - Minor Body size 1D-3, minimum 0
• Blt+MrBdy (no moons) - Belt & Minor Body of size 1D-3, minimum 0
• Terr - Terrestrial planets size 1D+3 fall within normal Traveller limits. Planets with size 1D+8 may be (~uninhabitable) super-Earths. Those with size 1-6 have +2 to moons, Size 7-14 gives +3
• GasDwarf (+4) - Gas Dwarf (⌀50,000 Km, ±1D x 5%)
• GasGiant (+5) - Gas Giant (⌀150,000 Km, ±1D x 5%)
• BrnDwarf (+6) - Brown Dwarf (⌀200,000 Km, ±1D x 5%)
  
  

Worked Example

I have only a UPP for the empnymous main world of the Vorlaga system A593787-9 and know it has a gas giant and a scout station. Let us generate a system to go with it.

1. On the system centre d66 I roll 25: G-type star, not multistellar. For Stars have a 50% chance of being smaller or larger than standard: Vorlaga's is to be smaller. I then roll 3 for size, 3 x 5 gives 15 % and 1,500,000 x 0.85 is 1,275,000. This gives a 100D jump limit of 127.5 million kilometres. (I forget to plot this until later).
2. I plot the system limits on the map
3. I roll 6D, finding I have 1 object on the 10M map, 3 on the 100M map, and 2 on the 500M map. I then roll for bearing and range for each object. In the example I have labelled these A to F. The innermost object, A, rolls 4 and 5: It is at 7:30 relative to the star and at 5 hexes (50M kilometre) distance. I repeat this step for the other objects. None are within the inner limit or beyond the outer limit, so no rerolls are needed.
4. I roll 2D for each object. A is starward of the hab zone inner limit and I roll 8: It is therefore a terran planet of size 1D+3, coming to size 8. I decide it has a 50% chance of being tidally locked and find that it is. I repeat these steps for all other objects.
   1. I find B is a belt and minor body sized 2, C an isolated minor body size 1, D a terran world, E is an empty orbit, and F is another belt and a size 0 minor body.
   2. I decide D is in fact Vorlaga and overwrite it with its UPP.
   3. I find I have placed no gas giant despite it being in the planet code. I could disregard this, and depend on this generator to supply or deny gas giants, but decide to just add one. I roll for map and placement, find it is to be within the habitable zone and 10:30 relative to the star, and randomly select from the three options for gas planets within this band: Gas Dwarf.
5. I add moons. Planet A is terran size 8, and so I roll 2D+3 for its moon count: 12, giving 1 moon. I repeat this step for the other planets. I decide not to bother rolling for size now except for Vorlaga's: I roll 4 and 1. Consulting the Moon Size table, 4 gives a moon 1/2 the size of Vorlaga itself, which is size 5. 1 gives a size 0 moon.
6. I have already placed my main world
7. I add space infrastructure and plot scanner limits (Having a type A starport, jump activity should be detectable within 1.5 B Km). I decide terran world A should have a poor quality (G type) spaceport. I belatedly plot the stellar jump limit: Planetary and lunar limits will only be visible at the tactical scale.