Traveller: Worlds per Subsector

Something I’ve noticed of late; the number of worlds per subsector in published products doesn’t match the number you’d expect from the rules as written.

Said rules have stated since 1977 that the typical subsector has a 50% chance of a world in each hex, which would give you 40 worlds on average. Some versions explicitly say it’s OK to modify the die rolls to give you a one-third (or two-thirds) chance, which would give you 27 worlds or 53 worlds respectively. Stars Without Number uses similar star maps and different rules, which still give about a one-third chance of a world in each hex; and the old GDW boardgames, Imperium and Dark Nebula, have a about one system per three hexes if you adjust the scale to one parsec per hex.

Published materials from Classic Traveller such as The Spinward Marches or The Solomani Rim use about a one-third probability, and more recent materials from Mongoose are using 25% or less, with 20% (16 worlds) becoming common. So I sometimes wonder why the official rules still cite a 50% chance per hex, when the publishers clearly aren’t using that, and as far as I can tell, never have. First world problems, eh?

This line of thought begs the question of how many worlds you actually need. Statistics from WotC and Sly Flourish suggest that the typical group plays every 2-3 weeks and plays a game for about five years before moving on. That’s for D&D of course, but I have no reason to suspect other games are different. That’s somewhere between 87 and 130 sessions, and while I’ve played in several games that hit the 100 session mark, I’ve only played in one that went massively over that, which I’m discarding as a statistical outlier. I have no idea how many sessions a typical group spends on a specific world; but in my games it has ranged from none at all to five or more, so let’s say an average of two to three.

Therefore, a campaign ought to need about 40-50 worlds; two subsectors’ worth at one world per three hexes, maybe just a single subsector at one world every other hex. Your PCs may well range over a sector or more, but they’re unlikely to visit more than a few dozen worlds; probably, the only reason you’re generating – or buying – hundreds of them is that you’re not sure in advance which ones will be interesting.

In short, a single subsector should keep you going for several years, especially if by design or blind luck it’s well-suited to your group’s desires; and it’s not likely you’ll ever need more than two subsectors’ worth of planets. If you’re ranging over a bigger region than that, more power to you, but you’re probably spending time detailing worlds you’ll never use.

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