• 13 Dec, 2025 *

I know my Traveller posts have a huge audience (last one was visited by 19 people!). Parts of this part of MyTraveller are not as well established because I just didn’t have inspiration to work on them. In general I would wait some more with publishing it but I had this situation where I wanted to check out old post "Worlds of Classic Traveller" at https://spooky.blot.im but the blog is empty. So I got to the Wayback Machine (shout-out to Internet Archive) to check it and I found it. If you want to check it out chip in for Internet Archive and search for it, it is there. I got shocked that this content vanished from the internet when I wasn’t looking. This post is just an iteration on sector and world creation in Traveller. And I have my OPINIONS about it!

Making Sector

Rules for Sector creation are easy. There are actually two main rules. Take or make a hex map 8 by 10 hexes (or take it from here https://spriggans-den.com/2025/06/03/sector-map-blanks-for-traveller-cepheus-engine-and-stars-without-number/) and make two rolls.

First roll is - is there a world in this hex. Roll 1d6 - results 1-3 mean this hex is empty, results 4-6 mean this hex has a solar system. You can of course play with variables, change the results to make sector denser or sparser, it’s fine but I quite like what comes out of the basic rule. Not too isolated, not too crowded.

Another rule is - is there a Gas Giant in this system? And here the general rule is roll 2d6, on a 10+ there is no Gas Giant. I have nothing against presence of free fuel but I would set it so on a roll of 5+ you will have a Gas Giant. If we keep the rule roll-high-for-positive then it shouldn’t be broken just for this one thing.

This is it. That is all for sector creation, thank you. World Creation Next.

World Creation (Next) - Starport Stuff

Here we stumble upon a contentious topic. From the get go. Starport. First minor thing is my another little issue with the naming convention. In general in pseudohexadecimal listing letters go from lowest A to highest Z. So 0 to 9 are numbers and 10=A, 11=B, 12=C et cetera. So it is weird that the best starport is A and gradually is worse with higher letter. I don’t get it but I could just roll my eyes and get on with my life but FOR THE LOVE OF UNIVERSE WHY IS THE WORST STARPORT X INSTEAD OF F? WHY? Starports are A, B, C, D, E, X? Why would you do this to my spicy brain?

So yeah, Starports for me go from A to F. Just substitute X from regular maps and materials into F. F is the no starport. Okay now to serious stuff. The way you establish which starport is where determines a lot about the overall setting. With sector it might suggest where in galaxy you are or how easy it is to get fuel but starport can suggest what is the political situation on interstellar level. Let’s see what various iterations say about that.

Classic Traveller: roll 2d6, and check the table. So far so good, simple.

Traveller Mongoose (second edition): roll 2d6, +1 if Population is 8+, +2 if Pop 10+, -1 if Pop 4-, -2 if Pop 2-

Cepheus Engine: roll 2d6 subtract 7 then add Population.

Why does the Population modifier so much of a difference? Well, the first edition of Traveller Mongoose clearly tells us that. The regular way is like Classic Traveller, just roll and get the result. But there is a mode called Hard Science that does it like Cepheus Engine - population determines it. To quote Mongoose: "In hard science settings, starports are typically built, owned and operated by the host world rather than some central governing power." Rolling starport type based on population implies that worlds are more independent and fund and service their starports. So it must mean that rolling randomly implies interstellar governing powers that potentially make, service and use these starports even on worlds with minimal population - the starport crew and population are probably separate entities. This is my take.

Okay so now what? Well, I started my adventure with Traveller from rolling randomly and I like it. I like implication that there are bigger things at stake, that the worlds are just an element of something bigger, greater, more cold and sinister. I remember I had to come up with a reasons for why some backwater worlds had starport type A. Does some corporation has business there? Is there some crucial industry? Did some very rich kids decided to make their own colony? Or why very populous world had starport E. Do they not want space travelers there? Don’t have the tech and resources and also don’t want external companies to make a starport for them? Is there a conflict with overhead "imperium"? Maybe sometimes interstellar community just doesn’t find a place important enough to make better starport here and wants really good starport in some place that doesn’t seem important? I really marks the intention of the overhead and I like it.

Starport established, what is next? Bases. Another contentious point on our map of various Traveller games. Classic had only Naval bases for military to station and Scout bases for exploratory service to station there. Cepheus adds to this equation Pirate bases. Mongoose doubles down and let us generate not only Naval, Scout and Pirate bases but also where are Research bases, and Traveller Hostels (and even Imperial Consulates in first edition).

What do I think? Well, do what you like but I like the Classic approach. At first I was fan of the more the merrier but I have learned that I actually prefer to do some things on my own. I would go for Cepheus version with but I would really like to set Pirate bases up myself. I feel like noting Naval and Scout on the map gives me and players the feeling of what do big players do. I would note the Hotels too, they are important for characters but besides that? So my setup is this:

• A has a Hotel automatically, and Naval base on roll of 8+.
• B has a Hotel on 8+ and Naval on 8+.
• C has Scout on 8+ and Hotel on 10+.
• D has Scout on 8+.
• E has Scout on 8+
• F has nothing.

The reasoning is this - starport of quality A or B means there is something valuable in the system, the world or the route it leads through. So it has a chance of having also Naval base for security or to ease travels of navy ships. Also high chance for Hotels, the luxury. The only difference is how serviceable is the shipyard and potential for Hotel.

C has small chance of having a Hotel, it’s like some company or government feels the potential and wants to entice traveller activity. C, D and E have also chances for Scouts, which means these worlds and systems might not be surveyed enough or there is some other scouting operation. I’m still thinking about the chances for Scout bases, should it be the same, or better/worse with poorer starport, I don’t know. I can see arguments for all options.

Then there is an F starport. It can mean that either the people of this world are hostile towards space travellers or that it is an independent pre-space culture and contact with this world is forbidden. Again there are heavy implications hidden in just simple type of starport. And then I can populate other bases as I see fit, dependent probably on trade routes and trade codes.

Environmental Building - Size, Atmosphere and Hydrographics

First one is quite obvious. Size. I wouldn’t actually change anything from here. For now. So something like this roll 2d6-2 and follow the table:

Size	Diameter	Gravity
0	<1000 km	negligible
1	1,600 km	0.05
2	3,200 km	0.15
3	4,800 km	0.25
4	6,400 km	0.35
5	8,000 km	0.45
6	9,600 km	0.7
7	11,200 km	0.9
8	12,800 km	1.0
9	14,400 km	1.25
A	16,000 km	1.4

Size does not change much but what implies next thing. Atmosphere. I’d like to point out straight modifiers - if Size is 0 then Atmo is 0. No atmosphere on asteroids or around space stations. If Size is 1-4 and Atmo is 1+ it turns into A which means Exotic. And it is that way because in such low gravity only xenon (and sometimes carbon dioxide) is heavy enough gas, lighter gasses simply escape into space due to low escape velocity. Only around size number five the conditions are met where you can have breathable atmosphere and livable temperature at the same time. Don’t believe me? Check this out https://en.wikipedia.org/wiki/Atmosphere

So then when we finally roll a world size 5+ then we have a regular atmospheric table. Roll is 2d6 - 7 + Size because size determines a lot in this case. Also something not mentioned in Travellers is that these are atmospheres after terraformation. If you really had worlds without terraformation you’d probably have all As, maybe some Bs, Cs and 0s/1s.

Result	Atmosphere	Gear
0	None	Vacc Suit
1	Trace	Vacc Suit
2	Very Thin (taint)	Air Supply
3	Very Thin	Air Supply
4	Thin (taint)	Filter
5	Thin
6	Standard
7	Standard (taint)	Filter
8	Dense
9	Dense (taint)	Filter
A	Exotic	Air Supply
B	Dangerous	Vacc Suit
C+	Unusual	Varied

It creates this unfinished picture that you have to fill in yourself based on your knowledge. Do you know that in thin atmospheres the winds are very strong and a lot of radiation gets in? And in dense it’s the opposite? Also the temperature changes are wildly different. That will be my basis for the "human species" in the future. So even as these are atmospheres after terraforming we can see tainted ones. It can either mean that terraforming didn’t go as far as planned or that the pollution came after humans settled the world. Also to those who know Traveller I didn’t separate Corrosive and Insidious atmospheres. I just don’t see the need of differentiation, dangerous is dangerous. Also it makes C+ atmospheres more common which I like. Inside the Unusual result are also things missing from MongTrav like ‘Dense, High’ or ‘Thin, Low’. All these crazy fun stuff you’d want your scifi worlds to have.

And now comes the Hydrographics. The amount of water on the surface of the world. There are some things to address here too, let’s check the generator first:

Result	Percentage	Example
0	0%	Desert
1	10%	Dry world
2	20%	Small seas
3	30%	Small oceans
4	40%	Wet world
5	50%	Large oceans
6	60%	Almost Earth
7	70%	Earth-like
8	80%	Small continents
9	90%	Sparse islands
A	100%	Water World

There are also additional rules. If Size is 0 then Hydrographics is 0. We assume if it is an asteroid you wouldn’t make a base on an asteroid made of ice because human activity generates heat and when melted the ice would escape. Aside of that if Atmo is 0 or 1 then Hydro has -4 to result. Unlike MongTravs and Cepheus I don’t think Exotic or Dangerous atmospheres should have -4 modifier. I think if the atmosphere is so different it means the world wasn’t terraformed and "water" in this case means any suitable fluid. Like oceans on Venus or something. When we get to atmospheres above 9 I think we get out of terraformed worlds so all rules get out of the window. Imagine Earth-like world but all the oceans are ammonia XD

As for regular atmospheres I consider only the A result to be a Water World. MongTrav and Cepheus consider result of 8+ to be a water world in the Hydro table but only A is Water World in Trade Codes it is another case of small decisions making mess in terms and definitions. One of the important marks is 40% - at this point the world is considered Wet World which means it can sustain wide agriculture and prevalent wildlife. Which also means all worlds under 3 are dry worlds. Which might impact the trade codes later.

Okay, I think this post grew a lot and is enough. Next time we get to Social elements of worldbuilding.

#Traveller