Assessing your local crystal sphere for campaign potential

tl;dr: roughing out your local crystal sphere can pay dividends in keeping campaigns consistent.

This is an extension of the 'high-mobility magic' discussion about handling your players rapid unlocking of access to huge new areas.

As part of early-days prep for my Home Campaign I rolled up the local crystal sphere, just to get a sense of what was out there and what kind of things would be visible when you looked at the stars at night. I was glad I did because a couple of odd local phenomena that would be obvious in the night sky revealed themselves. Lately the players have begun to contemplate travelling off-world after getting access to some higher level magics and so I have revisited that early prep to build it out some more.

Part 1 - Pre-campaign Prep (early 2020)

Starting out, I rolled up the local system using the AD&D Spelljammer system generation tables. This gave me the following roster of planets in the system:
0 - Sun - standard sun
1 - Sundisc - Fire type - Size H - Flatworld (Saturn-sized - 1/2 mercury orbit)
2 - Waterlens - Water Type - Size B - Flatworld - Earth Ring (Pluto-sized water-lens - Mars orbit)
3 - Great Ring - Water type - Size E - Belt - Earth ring (just past Mars orbit - Ring dwellers within earth-mass ice ring)
4 - Menagerie - Earth type - Size F - Spherical (Twice Earth sized with Asteroid-belt, 2 x moons - the game world)
5 - Fire Ring - Earth type - Size A - Cluster - Fire ring (Dwarf - sub-Ceres - Asteroid belt)
6 - Hinterworld - Earth type - Size C - Elliptical (Cold, pluto-like hinter-world - Uranus orbit)
7 - Twining Belt - Earth type - Size E - Belt - Earth Ring (Earth-mass belt - doubled by 'own belt' - Neptune orbit)
8 - Cluster - Earth type - Size D - Spherical - Cluster of Asteroids (Mercury-sized with cluster-moon - Far-frozen reaches)
Astral Boundary (roughly twice as far out as Neptune)

Below is a schematic with the long diagonal mapping the 'rings' of the system using the old Spelljammer notation. The closer rings (top left) are one day travel at Spelljammer speed, the further apart rings are two days travel apiece. The astral boundary is bottom right corner - so a fair ways out.

A bunch of interesting implications come off the random generation tables. First, I always look at 'where are the places to stand in this system' because when they are scarce, any real-estate becomes valuable. In Menageriespace, there is one 'standard' world, a bunch of asteroids, a tiny planet way out at Uranus orbit and a huddled cluster of asteroids out beyond Nepture. The asteroid belt between those last two planet at Neptune orbit is probably where most of the actual rock-by-mass in the crystal sphere is.

So we have one meaningful world, the campaign world - and while there is good fodder for space lairs and other such stuff elsewhere in the system, it means that for 'ordinary' ground-walking, air-breathing creatures, Menagerieworld is the only show in town. This is helpful to know as it means I will not have to clumsily ret-con why this other space-going civilization in what could have been the planet next door was unknown for the early campaign.

Of things that did become obvious and relevant is some really weird night-sky - and even potentially day-time - phenomena. First there is a saturn-sized flat fire-world in near-solar orbit, making this a mini-binary system. Then beyond Menagerieworld there is a fire-belt - manifesting something like our view of the Milky Way but brighter? A brightness in the sky?

Finally the other interesting phenomena was a water-lense world just in-system of Menagerieworld implying that far from solar-eclipses, everyone now and then this world gets 'blazes' where the sun is magnified through that water-world.

For the early campaign that was all I needed - that there were no obvious factions out there that I needed to account for and there were a few interesting night-sky artefacts I should mention in passing.

Part 2 - Late-campaign visiting potential (mid 2025)

After the significant on-world shenanigans, with the players flying around with their 'flying saddle' - a Spelljamming Saddle - they decided at last to poke into what is 'above the sky'. The sorcerer had always been able to feel a whole world of 'going faster' above his head - the saddles capability to punch up to Spelljamming speed once out of the gravity-well of their world - and after gaining access to teleport, they decided it was time to see what was out there.

They had in the interim ventured into the temple of a creator god and had to construct a model orrery of the local system so they had familiarity that there were things out there. The first things they decided to was visit the moon, which had been long threatened, so immediate work was to figure out what was on the two moons of Menagerieworld - but as part of that to also check who else might be wandering around in system.

Coming back to the system results I had worked up, I used the system-work-up techniques I had pulled together for running Light of Xaryxis and Spelljammer Academy and chucked it all on the kind of schematic you see above and generated a travel times table. The travel-times table makes it obvious that beyond the Fire-ring, forget about it. Everything within the Fire-ring is within ~ 1.5 days of each other, with it taking 5 days max to fly from the sun to the Fire-ring at Spelljamming speed. Beyond that, the howling wastes, with the journey times stepping up to a month, minimum.

So Hinterworld, the Twining Belt and the Cluster are all ideal places for ancient secrets to have hidden and survive over long aeons - potentially scope for mini-Lichjammer-esque attitudes; slow cycles of long duration plans.

Of all the systems I have rolled up, what becomes apparent is the large amounts of 'fire' real-estate - between the Sundisc fire-world and the Fire-Ring - and this seems like a good place there fore to say that there is a significant conflict between two fire-factions going on. Completely uncaring of the cold rocks elsewhere, they are competing for dominance of the fiery resources in this system.

This framing works neatly for me - there is a big conflict going on between two 'fire' powers who are just un-interested in the players homeworld - but there are things out there. There are plently of smaller places for things to be lurking about - ample opportunity to bring out lots of 'player scale' Spelljamming foes and random monsters without having to explain things like 'why, if there is a planet full of illithids just there, have we not been continually raided by mindflayer nautiloids?' The vast wildspace 'moat' beyond the cluster planet out to the astral boundary also offers good reason why this system is mostly left on its own.

I dropped in the Final Star from Bearded Devil's Apocalypse Archive appearing in the campaign's past - the fight to drive off the Cult of the Final Star being one of the 'fateline pinch-points' in the world history were most things went away. I think this can link out to the great fire-worlder conflict as the spark that has turned them against each other; all were against the Final Star but after fighting it off they fell to conflict.

So conceptually I think I will go with Lichjammer-esque undead and long-living, slow-movers out around the Twinning Belt, a simmering conflict between the fiery powers of the Sundisc and the Fire Belt, and standard Spelljammer encounters in the space around Menagerieworld, the Waterlens and the Great Belt. This is enough to rough things out if the PCs bolt for beyond-the-horizon, if they need more than that I will figure it out as needed.

The thing I have found that slips my mind time and time again is that Menagerieworld also has an asteroid belt as well as the two moons - so local space for Menagerieworld has a lot of real-estate, plenty of potential for adventure, wizards in towers and all that - and then a mid haul to the rest of the near-system and a long haul to the rocks beyond that.

In-game manifestations of off-world activity

Thus far the party has stumbled over just a few things - the classic crashed nautiloid of mindflayers happened a while back and they dealt with the escaped stock of Tzakandi. They decided to visit the moon and found a handful of things that various factions had stashed there to be 'out of the way' for time-abyss durations. The waxing and waning of the two moons played into the game in making night-time operations stealthy or not. They ran into some murdercomets on the way back from the moon.

From a practical point of view of where can I steal ideas for this - multiple moons and near-orbit rocks make Menagerieworld very similar to Faerun with the Tears of Selune and thus the ideas in Realmspace are available for inspiration if necessary. I plumbed Veins of the Earth for 'land out of time' ideas for the moon and Spelljammer 5e for wildspace encounters - once I had an idea of what analogues might be suitable it was relatively easy to run through and go 'fits, fits, no, no, fits, etc.'

Final Thoughts

The main value to doing something like this is that in just structuring out some rough stuff at high level you give some kind of consistency. One can always just make things up as it becomes relevant but going back to the heirarchy of truths at the table - if the players have something to grapple on to, they will make their own reasonable suggestions and conclusions based on their understanding of the world.