After a thorough review of dozens of science fiction PbtA games, and after hacking the last two TTRPG systems we played quite a bit, I decided to create my own game with exactly the vibe I wanted. 

Why not Starscape? That’s on my radar, as I’m a backer, but I’m waiting until it is officially published and has more third-party support.

Why not run another Impulse Drive campaign? That system is very “Apocalypse World…IN SPACE,” and I was looking for something gentler and more optimistic. I did borrow Impulse Drive’s framing around episodes, adapting its “Previously On” and “Cliffhanger” moves.

Why a new system? Well, I’d just published Reflections on PbtA Design, so it seemed apropos to design a game from scratch rather than just hack up an existing system. (Hard-Knock World started out as Dungeon World Level 0, and Uncommon World and Fantastic Worlds of course are a curated collection of third-party fantasy hacks to Dungeon World 1e.)

Dice Mechanic

I’d written about dice pools and used them in Hard-Knock World, so it was the logical place for me to start. PbtA games that rely on 2d6 tend not to scale their stats well (+3 succeeds 92% of the time), but I thought of changing the common pattern of 10+ gets you 3 choices while 7-9 gets you one to rolling as many dice as your stat and “On a 4+, choose one; choose an extra for each 6.” That way there would be more of a benefit to higher stats and with one die you could get three results (1-3, miss; 4-5, a hit; 6, an extra hit). In play, though, it proved too complicated. Players kept wanting to get a choice for each 4+.

I had forgotten that The Wizard’s Grimoire, which I’ve owned since 2019, just counts the hits (4+). That became the mechanic.

Source: Vincent Baker, Powered by the Apocalypse, part 11: Dice

Unlike The Wizard’s Grimoire, players can use skills and equipment to turn a roll of 1-3 into a 4+ so outright failure is much rarer than in a 2d6 PbtA system. The right skills can be essential: Alien Languages, Field Medicine, Shuttlepod Engineering, Piloting, Xenobiology, Caving Techniques, etc.

The caps on dice are unique. You can never roll more than five dice, but neither can you roll more dice than your Health (1-5) or the DIFCON level set by the GM (Difficulty Condition, from 1, critical, to 5, easy). For instance, attacking a sandworm has a DIFCON of 1, while attacking a droid might start with a DIFCON of 5.

Mixed Success

Unlike a 2d6 system, success is almost never total. If you roll a Yahtzee and get five 6s, then you get a lot of choices, but otherwise the GM is going to be able to follow your move with some logical consequences.

Take the move Hard Landing—

When you attempt to land a shuttlepod under dangerous conditions, roll OPS. On a 4+, choose one; choose an extra for each 6:
● Keep the passengers safe
● Protect vital cargo
● Minimize damage to the shuttlepod
● Land without being seen
● Land close to your intended destination.

Whatever options the pilot doesn’t pick, the GM can use against the players:

  • Keep the passengers safe – Not picked? Kill the redshirt. Harm one or more players.
  • Protect vital cargo – Not picked? When they go to Outfit themselves with equipment from the shuttlepod, let them know that what they want was damaged or destroyed.
  • Minimize damage to the shuttlepod – Not picked? I’ve created a random table of things that could go wrong for the GM to use or consult, if desired.
  • Land without being seen – Not picked? Some natives, sentient or not, have seen the shuttlepod come down. Perhaps there will be an ambush, or perhaps there will be a lot of explanations needed.
  • Land close to your intended destination – Not picked? Guess you’re going to have to travel a bit on foot first.

These lists of moves with logical consequences if they’re not chosen are my favorite part of the system. Not every move has choices that are so easily reversible against the players, but many do.

In practice, all results are mixed success: there’s never a full success. There’s enough movement to advance the story (something positive gets picked), but the GM can respond on any move by reversing something not chosen.

Move Design

Playbooks are actually two inserts: one for your character’s background (cyborg, cross-cultural, telepath, etc.), one for your specialty (pilot, doctor, security, etc.). As I designed playbooks, it’s been fun to re-re-read Vincent Baker’s long series of blog posts on PbtA design. 

One method that he didn’t mention for move design that works well for me is starting with the name. Kirk Fu. Dark Place That Knows Things. From Hell’s Heart. Stone Knives and Bearskins. Not the Droids You’re Looking For. Translator Microbes. I’m a Doctor Not…

All those moves came to me first as titles, then I had to think through what they might look like in play.

Hacking

Another reason to design my own game from scratch is because of how much I’ve been hacking rules lately anyway, integrating all my favorite bits from other systems:

  • We’ve started our last two campaigns adapting Stonetop’s introduction moves, so I rewrote those for a science-fiction setting and baked them in. One player said it was the best way of connecting new characters he’d ever seen in a PbtA game (all credit to Jeremy Strandberg).
  • I like having a formally defined catch-all move, so that’s there, with a nod to BSG: “Sometimes You Gotta Roll the Hard 6—When as a group you can’t agree which move applies, but agree that success is possible but not certain, brainstorm what aspects could go right. Roll a die. On a 4+, choose one; choose an extra if you roll a 6.”
  • I’d experimented with a 5e-style skill system for Dungeon World, and that’s now the core mechanic for mitigating bad rolls.
  • I’d also written about our experiments with away moves, so that’s now formal, with this episode move: “Cameo—When a player is absent for a session but you want to use a move their character is known for, spend a Teamwork die and use their move as if they rolled a 6. Any harm that might befall this character applies to your character instead.”
  • The Flashback move that I adapted from AW2 makes another great “Episode” move.
  • In all my recent campaigns, since I’ve tinkered with a Starting Move as well as customizing the End of Session move, it was nice to just write those up in the way that I find most useful.
  • On the GM side, I talked up bringing in worldbuilding as a GM move, so that’s present.

Of course, the full text of Planet of the Week is licensed under the Creative Commons, so that others can hack on it, and it can be part of the PbtA Commons that I’ve loved so much.

Combat

I’ve gone back and forth on combat. Initially I had just Kirk Fu (for dramatic over-the-top fistfights, named after this book) and Return Fire (can’t be used to fire first). But players wanted additional moves, so now there is Han Shot First (for starting a firefight) and some more serious moves (Take Cover), but while writing them all I tried very hard to see them through the lens of TV episodes, especially episodes of Star Trek: The Original Series.

Campaigns

I’m running three campaigns with the system. For the one where we used Microscope to flesh out the world, our touchstones are Star Trek: Enterprise but without the magical tech (transporters, replicators, warp engines); heck, that group doesn’t even want long-range sensors, which is fascinating. We can travel FTL, but we can’t see what’s there until we do. “Hey, these scans show a massive starship 4 light years away, but that was 4 years ago.”

To explore your own universe, you can download the Player and GM Guides for Planet of the Week from Itch.io.