"Hex-Crawling" the Shackleton Expanse

Sorry, I just had to throw that in. :grin:


@Modiphius-Jim This one’s quite a bit technical, but:
Chapter 10 (Stellar Cartography) of the Shackleton Expanse Campaign Guide repeatedly refers to “Class O” spectral class/type (cf. e.g. p. 303, modifiers table on p. 305). Yet, neither the Spectral Class table, the Special Spectral table nor the Notable Spatial Phenomena table contain any O-type stars.

What am I missing? :slight_smile:

Wikipedia says that L/Y/T are categories of red and brown dwarf, so it feels like there’s some redundancy between the L/Y/T and the Brown Dwarf categories on the Special Spectral Table on pg. 303.

Page 303 also has this line, “Note that results of II, II, Ib, or Ia along with the spectral type…”

Is Luminosity II simply repeated, or should the first instance say III?


I stumbled over the same issue and decided to interpret it as a typo. So, it probably should indeed say III.

If we don’t have ‘O’, then we can’t use the mnemonic, “Oh Be A Fine Gorn, Kiss Me”.


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maybe it helps

Naw, we’re talking Class O stars (the great big blue giant stars), not Class O planets.

It does seem like they’re pretty rare, though.



Yep rare, young,
Interesting * θ1 Orionis C is the brightest star in the Trapezium cluster in the Orion nebula, an O6 main sequence star with a fainter spectroscopic companion.
Maybe Orions can telll more

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I use this as a reference for my games:

Yes, but where is it (= the O-type star) on the random tables in the Shackleton Expanse Book? :slight_smile:

Seems to be missing. It should be in the Special Spectral Table. I’d modify it that a 4-5 means Class B and 6 means Class O. The rest stays the same. Class A is more abundant than Class B, so changing the table this way makes sense to me.

Don’t recall what happened since the book was done more than a year ago. Here’s the special spectral table from the pre-layout draft. Maybe this helps?

1-2 Class A
3-4 Class B
5-6 Class O
7-11 Class L/Y/T
12-13 White Dwarf
14-15 Brown Dwarf
16-20 Roll on the Notable Spatial Phenomena Table

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It is for a different game but Coriolis Atlas Compendium has a pretty quick set of tables to generate systems and planets that should work in just about any setting.

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Looks like Type O got cut from that table, and the numbers were changed. Most notably (other than Class O’s cut) is that the Notable Phenomena table is now just at 20, not the whole 16-20 range.

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Which, I guess, seems reasonable give the rarity of the star type.

Even if you made the O-type Star the result if you roll a 20 on the Notable Spatial Phenomena Table, one of them is likely to happen in 1/8000 rolls (you’d need three 20s, or 0.000125% frequency). That means, in game terms, that the O-class Star shows up an order of magnitude more frequent than current science believes (~0.00003% frequency).


Actually, since there is technically more than one “Notable Spatial Phenomena” table… (the probability to get a T-Tauri star is 1/40,000 if all sectors are evenly distributed among the… regions that are called sector, too). :wink:
It would still be fare off, though.

That would line up with @bcholmes’s ~0.00003% (1/40,000 = 0.000025%)

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I have a bunch of other questions. Some of these fall into the realm of “I’m trying to apply science-y math to a fundamentally math-light set of rules” but I have difficulty ignoring real world science, even if it’s in a realm that’s not fully understood.

So here are my questions:

  1. The Shackleton Expanse book uses some planetary classes that do not appear in the Core rulebook. I think, mostly, there’s enough information about the classes to understand what they are. The one I don’t fully understand is the Class-I (Ammonia Clouds) class. The Star Trek: Star Charts book describes Class-I planets as gas supergiants (not to be confused to gas ultragiants, Class-S and Class-T). Are these two Class-I designations describing the same world? The Star Charts book uses this text: “Tenuous, comprised of gaseous hydrogen and hydrogen compounds; generates heat.” Ammonia is a hydrogen compound. Is that what’s being described?

  2. There are, sadly, no instances of Class-H, Class-N, Class-T or Class-Y generated by the tables (there are a bunch of other classes, in Star Charts, but those four are listed in the STA Core book).

  3. The Inner Worlds Table and the Outer Worlds Table are the same (in my v1.1 version of the Shackleton Expanse book). Is that right?

  4. Some other RPGs (e.g. GURPS: Space) assert that most giant stars (e.g. Luminosity Ia, Ib, II) don’t have planets. There doesn’t seem to be anything in the rules about that.

  5. A thing I have difficulty wrapping my head around: the primary world’s orbit number is generated by die roll. I can, for example, roll up an M5V with 7 orbits, where the primary world (a terrestrial planet) is in orbit #5. But a star that insubstantial has a very close garden zone. (GURPS: Space says 0.1 to 0.2 AUs; Star Hero argues 0.025 to 0.042 AUs). If my terrestrial world is that close to the star, it seems unlikely that there are four inner orbits containing other planets. (Maybe I should imagine that the terrestrial world circles a gas giant that’s providing necessary heat?)


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  1. That’s the same in my version. I suppose that the tables could be differentiated, perhaps with a heavier weight towards iceballs for outer planets, and maybe the addition of class Y for inner?

Of course, that leads to the issue you raise in 5: random rolling planet orbits leads to what is perhaps unscientific, in that stars have certain energy outputs that might determine planet types in a way that contradicts the dice. I suppose the planet tables could be expanded with certain tables per star type, or something…

But the question is does it matter? It might for a number of Star Trek fans (and I would prefer leaning to real-world accuracy and canonical consistency), but for a casual game, is it enough to just say ‘here’s a star and its planets’? The nice thing about an RPG is that you can do whatever you want, whether it’s because ‘hey it turns out Starfleet discovered loads of planets around Ia, Ib, and II stars’ or ‘this super powerful ancient race decided to experiment with planet building here’ or ‘that’s just how the system is’.

There’s also perhaps an argument to be made that most Star Trek games will focus on class M planets, and just the planets, which is what I recall most Star Trek episodes doing. Sure there’s other stuff in a system, but unless it’s plot relevant, I would assume the GM would just handwave it to an extent. Plot relevant system items or non-M planets are likely to be more involved than a dice roll generator anyways.


For some roleplayers, world-building (or, say, star system building) is as much fun as playing in said systems. The Traveller group I occasionally play in has (repeatedly) spent entire sessions on collaboratively going through the same random tables over and over again, coming up with great (back)stories on each walkthrough.

For some GMs, random tables are an add-on because the randomness sparks ideas they never had before. Take e.g. the GM that focusses on M class worlds (because they’re so predominant on screen) who, because of the random tables, has to think of a plot set on a Y class demon planet, because that’s what the tables gave them.

And for some GMs, random tables are great to reduce preparation time. You never know when a player asks “okay, and what besides this M class planet do I survey in this system?”. If you got random tables, you can just open them, take a few dice and answer, smiling: "Well, let’s see… :wink: "
The randomness will guarantee that not all systems have a medium sized yellow or a big red star, one M class, one gas giant and an asteroid belt…