Low Prep, Rich Traveller Campaigns : A Game Structure Overview


This is a Low Prep RPG Philosophy article.

In the Traveller RPG, if you are creating your own setting rather than an existing one such as The Third Imperium, you use the classic mechanism of taking a blank sector sheet, populating it with stars and generating the planets. This procedural generation mechanic basically produces isolated worlds with some trade and travel mechanism between them that you can build a bigger picture on to. However, if you want to create a large scale setting where space nations covering territories of a hundred parsecs across and intergalactic friction between them, then as a game master you have to do a titanic amount of detail prep to determine what space nations emerge that are consistent with the star system detail. At the same time the planets themselves and the star systems end up being a little lacklustre, the Scouts supplement notwithstanding.

This article will start to provide you with a basic development structure that provides a way of making wide ranging Traveller campaigns, spanning large regions of space and including many astro nations, alien species, conflicts and ancient mysteries, star systems with many planets and complex economic and social systems, all while retaining Traveller’s core world/star port mechanics. The methodology itself is aimed at creating interesting role play situations while limiting the amount of preparation the game master needs to do for each session.

The Problem

Classic Traveller presented a simple mechanism for generating the worlds for play. Print a sector grid, roll the presence of systems in the hexes. For each system randomly determine a star port class (A through E, and X for none) that then modifies the one planet in the system we care about. For that planet roll up its physical characteristics and let them modify the social characteristics of population, government type, tech level and law level.

There was some intent that the game master should tweak to taste but no mechanism for handling interactions and influences between star systems, allowing for the idea of a “nation” that covers many star systems for example. This lead to a standard approach of rolling up sectors randomly and plonking players into them hoping that a game would evolve around them. This actually did happen but it was a lot of work.

The Third Imperium campaigns eventually provided more in the way of a big picture but the star systems had to conform more to imperial structure and there was still a sense of vacuum for a new game master to fill somehow. Interestingly mapping the Imperium in technical detail outstripped the adventures that seem to have been played within it. Have a look at the Traveller Map for a truly impressive example.

A number of GMs longed for more detail within a star system and they were rewarded with Book 6: Scouts which contained a method for generating the other planets and features of a star system.

All in all these mechanisms lead to a lot of work, a lot of which would not get used, and which didn’t really create much in the way of a sense of a real universe or interesting situations for the players to play in.

One of the things to note is that the purely mechanical value set for planets did integrate into some broader mechanisms that have an impact on the player’s general play routines, especially if they did any interstellar trade, so simply declaring things to be one way or another by game master fiat could lead to mechanical breaks in the system.

Any system of campaign creation would need to leave much of the Traveller nuts and bolts in place or create a whole new system of handling trade and economics. I didn’t feel like doing the latter so over a period of forty years I evolved a way to define large regions of space from a “what is interesting to players?” point of view that, when you zoom down to a star system still has the old traveller basic numerical descriptions in place so that the other systems still work as designed.

The New System

There are four levels of campaign prep that a game master should work through in order.

  1. Astro Nations
  2. Sector-ish Regions
  3. Star Systems
  4. Planets

Each level contains slightly more resolution detail than the one above but also has a smaller initial preparation area. The higher level detail constrains the lower level detail to conform.

The player locations will determine the coverage of the different levels of detail. The lowest level within a jump or two of their location, star systems within about 4 jumps, regions the one containing the players and maybe adjacent ones if they are near the edge and nations covering the likely extent of the campaign.

For the players they will have access to the information at all four levels that encompass their current location. So they will be effected by the details of a planet they are on, the star system they are in, some intrusion from the star sector-ish region, particularly knowledge of surrounding star systems at level 2 detail and regional factions that operate in their current system, and similarly they will know about Astro Nation level big picture stuff from their characters background, news services, history information and so on.

Level 1 : Astro Nations

The new system starts zoomed out to the level of “astro nations”. At this level you mark out the extent of various groups on a map of the galaxy. You decide what their main species is (or species mix), their basic nation structure from “anarchic” through to things like “hierarchic” and “distributing”. You also need to know the highest tech level available and how old the nations are, which is used to guide the size and qualities of the national extent in space. A nations boundary is limited by how far a ship could move at the maximum available jump, but realistically the growth of a nation is likely to be far less than that as it probably takes around 30 years minimum to colonise the outer fringes to a distance of ten jumps from settled territory. You may also want to create a historical timeline.

At the scale of nations you should consider one or two large scale “factions” that operate within or between the nations. Also include national internal structure such as hierarchic principality regions or economic trade blocks. You may also place some important star systems within the nations, merely describing their name and role, such as capital and trade hub worlds or ones that are in some way legendary. All this is intended to provide some broad brush stroke flavour for players and to give the game master context for a living galaxy where things play out.

Nation Structure

Anarchic The “nation” is a loose alliance of trading partners with no central authority and no inter system rules. Agreements are built on trust from reputation.

Heirarchical The nation is organised around strong central government that devolves to subordinate systems themselves governing subordinate systems. Strongly enforced laws govern system relationships.

Collegiate The nation has a collection of political/economic hubs containing multiple star systems each. The hubs relate to one another by mutually agreed laws and representation at national deliberations.

Nation Wealth Flows

Concentrating The national wealth tends to concentrate in a few hands.

Distributing The national wealth tends to be redistributed to keep everyone reasonably even.

See the Astro Nation example for the Free Terran Confederation campaign.

Level 2 : Sector-ish Regions


Once having sketched level 1 out then you determine where your player group will start (or if you are daring then you might decide where your multiple play groups will each start. Be Warned: if they all start far apart then there is more prep than if multiple groups start in the same region).

In the player’s start area you want to know what is within about four weeks easy travel of the player starting system, based on the likely jump speed the players will be able to use. In that area you will place stars and determine if they play a role in the nation or nations that cover this region. Their roles will be things like national capital, regional capital, trade hub, population or cultural centre, mining system, science outpost or military hub or outpost, mere fuel stop, or a very early new colony. General colony systems fill in the space between the more specific ones. (level 3 : Star Systems explains the designations in more detail). The actual details of planets and star ports are not created at this level.

In addition you will want to know about the presence of a few more rare things, such as special stars like neutron stars or black holes, large nebulosities and areas of space dust, or other alien species that are non-space faring or have small space faring colonies embedded within the larger nations space. Once more there are purely mechanical systems for designating these or the GM can select what is desired. These rare items are placed in the prepared area before the details of other star systems are considered.

Also at this level you can include some regional factions. These operate at a lower scale and with more regional focussed agendas than the nation level factions, and may be sub parts or in the service of the larger factions. You will also want to block in relationships between star systems such as who colonised who, what are the xboat routes for communications, express freight and express migration pipelines. More detailed communication and trade route detail can’t be provided until we flesh out level 3.

This middle tier of detail will expand as the players travel about. Between sessions you may expand the tier further than the 4 week travel rule of thumb, if it seems appropriate. It is also ok to make up some middle tier design on the fly during play if needed, but then solidify and expand out between sessions when you get the chance.

A quick note about xboats

Capitals will be connected by communication xboats to major systems such as trade hubs, other capitals and military hubs.

Trade Hubs will be connected by freight xboats to their sources and clients. Freight xboats are given over to cargo and are serviced by tug tenders that bring them to and from freight yards.

Migration xboats are given over to carrying large numbers of passengers from established worlds to the expanding regions of a nation. Tenders include shuttles to in-system destinations. Such xboats carry passengers, small goods and mail on their return journeys.

Freight and migration xboats also carry mail, though with lower capacity than communication xboats.

See the sector example of the Free Terrain Confederation Campaign,

Level 3 : Star Systems

For the player’s starting system and each of the systems within about two weeks travel you will want to have a bit more detail prepped.

At this level you will designate a star systems general content. You should already know the role it plays in the Astro Nation from the 2nd Level area encompassing a star system and that role will constrain the nature of the star system to some degree. (In “reality” the nature of the system would have been responsible for the system attaining its role but that throws us back onto the classic traveller development paradigm)

Level 3 detail includes knowing the physical details that there are one or more gas giants present, how many other planets are present and if each is an asteroid belt, or a rock, harsh, marginal or garden world designation. You may also note the number of significant sized moons or rings the gas giants have and the moons may also have physical type designations, the same as the planets.

The social information includes that the system has life, its general economic status, star port facilities, general population level and the number of fuel facilities and in-system refineries, space habitats and express ship (communications, freight, migration) tenders and general schedules, and bases for astro national services such as navy and scout bases and supply depots. As mentioned this information is constrained by the Level 2 role of the system, and will itself constrains the level 4 detail of each planet.

Governmental and cultural forms are likely to be variations on those generally found in the region of space around the star system, with strong influence from the founding star system forms for the original colony and from current trading and cultural exchange partners.

Again, as players move about you will want to keep some level 3 detail ready out to about two weeks travel. If you have the level 2 detail coverage for the system its also easy enough to create some of this on the fly during play and solidify later between sessions.

System Role and Likely System Contents


capital-star-cityStarports represent the level of facility throughout the system. You should consider how that translates to landing sites, space elevators, highports and navigation satellites on each planet. Refined fuel is going to be available at star ports and possibly at refinery facilities orbiting the gas giants. Unrefined fuel may be provided by regular scoop operations in the gas giant orbits as well.


This system considers the population level to indicate the population of the star system as a whole. In class A and B starports there will likely be a number of space habitats with sizeable population numbers. No system playing a role in the nation has population of 0 unless allowed specifically by the system role.

Capitals will have a major source of fuel, most often one or more gas giants. They are also highly likely to have a garden world and 1 or more marginal worlds. Starport class is A. Population level is 7+.

Trade Hub systems Have a good source of hydrogen either through gas giants or planets with high hydrographics with water as the liquid. Their nature is largely due to their position in relation to other systems so the rest of the system make up is unconstrained. Starport class is A. Population level is 4+.

Population or Cultural Centre systems will have at least two planets that are each either garden or marginal.They also have a good source of hydrogen either through gas giants or planets with high hydrographics with water as the liquid. Starport class is A or B. Population level is 8+.

Mining Systems won’t have garden worlds or more than 1 marginal world but they will have an abundance or asteroids and rocks. If they don’t have a source of hydrogen then it is shipped in from a nearby system. Starport class is any other than A or X. Population level is 5-.

Science Outpost systems won’t have garden or marginal worlds but will have interesting harsh worlds or other unusual phenomena. Neutron stars and black holes will generally be science outpost systems. Starport class can be D through to X. Population level is 5-.

Military Hub or Outpost systems do not include garden worlds. They do have a good source of hydrogen either through gas giants or planets with high hydrographics with water as the liquid. They may have some mining activity and associated manufacturing. Hubs always have starport class A, while outposts can be A through to C. Population level is 4 through 6 for a hub, 4 or 5 for an outpost.

Fuel Stop systems have a source of hydrogen, a gas giant or harsh planet with high hydrographics with water as the liquid, and little else other than asteroids or rocks. Starport class is either E or X. Population level may be 0 and not more than 4.

Unused systems should have no gas giants, and their few planets should be asteroids or rocks or at most a single harsh planet that hasn’t been worth the effort to colonise or exploit. Starport class is obviously X. Population 0.

New Colonies will have planets appropriate for the type of role that colony is going to play, as a population centre, mine, trade hub and so on. The starport facilities will be undeveloped, usually rating two classes lower than the starport class it will become. Population is constrained to level 5-.

General Colony systems are unconstrained as to their system physical properties. Their population level is 7-.

Unexplored systems are free to have whatever composition is appropriate.

Level 4 : Planets

At this level of detail you are back to the Traveller planet generation system but constrained by the information from levels 1 through 3. You will only want this level of detail on the important player home system planets and some of the planets within a single weeks travel. In some cases such as with rocks and asteroids you may still leave this level of detail out as the players are unlikely to visit them unless you hook them to those locations.

You can apply the constraints to the normal Traveller world generation mechanism but you may also want to generate the planet wholly or partially by GM fiat as suits your game mastering style and circumstances. The constraints give you guidance in this, making it all much easier.

You should be able to wing playing on worlds without this level of detail much of the time and use it to provide some jostling up of your planetary design when needed or when players need to know a specific detail.

Separate out the physical characteristics and the social ones. The social characteristics (government style, law level, tech level) of a planet will be considered the same as those for the whole solar system (level 3) unless otherwise specified. You can designate the “main” planet of the system as being the source of those things. It may be useful to have some things such as law level vary in system but tech level is unlikely to vary across the inhabited planets in the system as they can acquire what they need easily from one another.

Star Systems also have local factions and interplanetary relationships that should be noted.

Mapping Planet Types to Traveller Stats

At the level 3, star system detail the non-gas giant worlds are designated as asteroid, rock, harsh, marginal or garden. When generating the physical characteristics of such a world using the Traveller system the following limitation applies.

Size, Atmosphere, Temperature, and Hydrographics values each have a designation type they are appropriate for. Garden worlds being generated may only have stats marked as appropriate for garden worlds. Each lower quality world may have the stats marked for it or any higher quality designation, as long as at least one stat is specifically marked for the designation of that world. So a harsh world could have a standard atmosphere, which is a garden stat, but then its temperature or hydrographics must be one of the designated harsh world values.

Size Size 0 is asteroid. Size 1 and 10 are harsh. Sizes 2 and 9 are marginal. All other sizes are marked garden.

Atmosphere None, trace, very thin and very thin tainted are rock. All the other tainted atmospheres, as well as exotic, corrosive, insidious, very dense and unusual are harsh. Thin and dense are marginal, and standard and low atmospheres are garden.

Temperature Freezing and boiling are harsh, hot and cold are marginal, and temperate is garden.

Hydrographics 0 is rock. 1,2,9 and10 are harsh. 3,4 and 8 are marginal. 5 to 7 are garden.

Tech Level on all planets is limited by the Astro Nation’s tech level. Exceptions should be carefully placed by the game master.


This is a broad brush stroke structure. I have been using it for a long time in general but this is the first time I have given it clear substance. You will note I have not included detail mechanics, other than mapping physical stats to planet types. I have them, and I intend to provide them in future articles, but they need some more work. One reason for that is I have a number of mechanics that I actually use more heuristically than mechanically, and I need to spend time capturing how I do that and including it in the detail descriptions.

There are also ways in which I break out of this four level structure that need some thinking about. For example I sometimes build level 4 detail star systems and plonk them into areas that have only level 1 detail. That is as a seed or guideline for sketching the nature of a nation early on. I also do that for uninhabited worlds on the periphery of a nation where I anticipate players may go exploring.

Other structures to be covered include creating alien species, building unique cultures for their home locations and integrating different species into nations. Also managing law levels across nations and regions, which ties in nicely with the smuggling scenario structure.

However this article should have given you enough to act as a guide for developing your own campaign using it. I hope you find it useful.

The next article to look at from here is Low Prep Traveller Factions : Basics where I describe how to create factions at each of the four scope levels.

My Patreon site now has a PDF that covers a new 6 x 6 hex map for use with Traveller, including a 3D option map.


3 thoughts on “Low Prep, Rich Traveller Campaigns : A Game Structure Overview

  1. Pingback: Traveller : Astro Nations Example – Strange Flight

  2. Pingback: Low Prep Traveller Factions : Basics – Strange Flight

  3. Pingback: Low Prep RPG Philosophy – Strange Flight

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