from the introduction:
Welcome to Spacejammer, a periodic zine of 90s-style adventuring in fantasy space. This isn’t the space of our physics-bound modern world, but a magical space, loosely based on early modern ideas of the aether and crystal spheres, where gravity is always earth-normal (until suddenly it’s not there at all) and everyone carries their own atmosphere with them when they take off into the void. While inspired by the 1989 boxed set Spelljammer: AD&D in Space from TSR, it’s designed to work to play with Troika! Numinous Edition and requires a copy of that game.
While adventurers may be from anywhere in the known (or unknown) multiverse, these backgrounds assume that our fantasy adventurers (who should combine nicely with most Troika-compatible backgrounds) begin in the Asteroid Duchy of Braull, where the openly corrupt Duke Dru oversees a miniature city state of merchants, pirates, and explorers.
Create your Troika! Numinous Edition characters as normal, but use these backgrounds instead of (or as optional replacements for) your normal set.