building the 1 page spelljammer rules

My D&D campaign usually keeps its feet on the ground, but I like the idea that it might spontaneously find itself in space at any time. Here’s how I imagine that going: “Oh no, the PCs went through the Star Portal! I’ll break out my copy of Spelljammer. OH NO IT’S 200 PAGES! THIS BOOK IS TAKING TOO LONG TO READ! THE PCS HAVE ALREADY IMPLODED IN THE VACUUM”

So here’s the plan: I’ll start with the Spelljammer rules, simplifying wherever I can, and try to synthesize something more concise, like ONE PIECE OF PAPER. (I think most rules subsystems should fit on 1 piece of paper, with illustrations if possible.) My design musings follow (they’re significantly longer than 1 page). At the end of the process I’ll cook up a 1-page ruleset for D&D space exploration.

OK, first of all, the Spelljammer boxed set spends 7 pages explaining the concept of D&D in space. I think we can do that more economically. At the top of our page we’ll write

D&D In Space


The next 35 pages are spent on explaining the physics of Spelljammer space. Here’s the short, slightly mangled version: each star system is in a crystal sphere. What we perceive as stars are lights on the inside of the crystal sphere. Outside of the spheres is the phlogiston, a rainbow-colored gas which is difficult to traverse. Cosmic currents connect certain star systems with each other, making travel possible along certain narrow routes.

You know what that sounds like? Rooms, walls, and corridors. Space travel, in the Spelljammer model, is more like dungeon travel than wilderness travel. I like this: dungeon travel nicely limits PC choices, and, in a lot of ways, makes things easier for the DM. A starmap might use a lot of the mapping conventions of a dungeon map. In fact, it occurs to me that you could use any dungeon map as a starmap, with rooms representing solar systems, and corridors representing the twisting paths of cosmic currents.

On the other hand, while I like the travel-limiting implications of the crystal spheres/phlogiston model, I’m aware that the model itself is not for everybody. You might like it fine, or you might want to use a more traditional sci-fi model, where space looks like space, not the inside of a rainbow, and the stars you see are actually stars, not twinkly lights on the inside of a Dyson sphere. Or you might want your starships to sail on a literal astral sea. Basically, every DM is going to use their own cosmology. Rules must be flexible here.

So here are my space physics:

Space is a dungeon. Just as players venture blindly down dungeon hallways, they must chart astral routes (phlogiston currents between crystal spheres? solar winds? hyperspace lanes?) You can even use an existing dungeon map as your star chart, treating rooms as stars, rubble as asteroid fields, stairs as wormholes, etc.

Maybe you don’t have a copy of the Temple of Elemental Evil on hand to act as your star map. In that case, I’ll provide the simplest possible star-map generator:

Star systems are connected to 1d4 other systems.


The Spelljammer physics section also has a bunch of stuff about how Spelljammer ships work: apparently they have gravity planes, atmosphere bubbles, and different speeds within the crystal spheres and the phlogiston. This is all pseudoscience to explain Spelljammer’s central conceit: D&D space travel works pretty much like D&D nautical travel. Let’s skip the pseudoscience and keep the conceit.

D&D space travel works pretty much like D&D nautical travel. Translate space ships into equivalent sea ships (cog, warship, galley, etc).

What does it mean for space travel to be like nautical travel? Are we talking rocket ships or sailing ships? Cloth sails? Oars? Water?? Can you stand on deck and breathe the star wind, or will you implode in the vacuum? The answer to all these questions is “dunno, maybe!” It’s up to the DM’s cosmology. In mine, sailing ships are pushed through space by solar winds. Galleys aren’t driven by literal oars, but by other labor-intensive or fuel-intensive methods of propulsion: stokers who shovel coal in steamships, for instance. The important distinction between sailing ships and galleys is that the latter are less dependent on the weather. I think that it’s good to preserve these two ship categories.

Astral forces push sailing ships, while galleys are self-powered.

I’d also like the space travel rules to be consistent with existing ship travel speeds. Every D&D edition measures ship speed in miles. You should still be able to use all the data in a ship’s stat block, even though the distance between stars might actually be billions of miles.

For every sea mile a ship can travel, it can move 1 “star mile”.

Exactly how big is a star mile? Who cares?

I’d like to add a tiny bit of crunch here: what are the distances between stars, and thus, how long are space journeys? The Spelljammer book doesn’t actually get into that, leaving large-scale mapping entirely up to the DM. My intuition is that traveling from planet to planet should be sort of like walking between nearby villages, and travel between stars is like journeying from town to town. Travelers should be able to reach their closest astral neighbor in a few days, and go from from outer planets to the sun in a few hours.

Systems are 1d20x10 star miles apart and 2d10 wide.


Spelljammer spends thirty pages on rules for space combat. (Space combat is remarkably similar to D&D naval combat.) All the usual suspects are here: ramming, boarding, ballistas, Greek fire, etc. In fact, Spelljammer has one of the best D&D naval rulesets! But, since it’s so similar to standard naval combat, which is discussed in more or less detail in various D&D editions, I don’t need to spend much room on it here. Personally, I’ll be using my one-page naval rules.

Space ships use D&D ship combat rules.

D&D editions tend to have roughly the same types of ships, with a few name changes. In the interest of cross-edition compatibility, I’ll list all the ship classes and their variant names.

Ship types: keelboat/barge, small galley/longship, large galley/trireme, merchant/sailing ship, warship.

OK, so far we’ve got a rough idea of how space ships travel and fight, how star systems are connected, and how to make a star map. And we’ve filled way less than a page.

steponeeI think it’d be cool if my space rules end up looking like one of those Copernican solar system diagrams. I’ve sketched out a sun in the middle: I’ll fill that with rules about star systems. I’ve left room for planets orbiting the sun: I’ll fill them with planetary rules. (What’s on each planet? Who inhabits it?) And don’t forget moons! And random space encounters!

That means that all the rules we’ve come up with so far – the general space-travel, combat, and starmap rules – should be tucked into “outer space” in the corners of the page. As you can see, they fit with plenty of room to spare.

Next time I’ll get into random space encounters, and maybe draw pictures of some deep-space D&D monsters.

7 Responses to “building the 1 page spelljammer rules”

  1. Bobby says:

    Have you read White Star? It’s not quite after the same thing, but I would think you could lift the space travel rules for a D&D game.

    Full disclosure: I haven’t received my copy yet, so this is based solely on reputation.

  2. paul paul says:

    Is White Star more than a page long? 😉

  3. Bobby says:

    Yeah, but it’s a whole bolt-on system for playing classic sci-fi using OSR D&D rules.

  4. Michael "Gronan" Mornard says:


  5. Carl says:

    This is fan-damn-tastic! Seriously. I love this blog. I love one page of goodness. Your boat rules and the paired down Spelljammer rules is PERFECT for a game I’m DM’ing right now. Literally this Thursday my group are going into space. Internet high 5!

  6. Carl says:

    So good! Thank you for all this!

  7. Andrew says:

    Question: How much more expensive are spaceships compared to regular ships?
    Looking at real life comparisons and gameplay aspects it seems like anywhere between 20x to 100x seems good.

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