World Builder's Handbook - Designer's Notes

MongooseMatt

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The forthcoming World Builder's Handbook is still a little way off, but I thought some of you might be interested in seeing the designer's notes for it...



Traveller has existed since 1977, and its advanced star system generation system appeared in 1983. As mentioned in the introduction, the initial attempts in Book 6 Scouts and the World Builder’s Handbook to create whole star systems for Traveller were hampered by a single data point: the solar system. By 2022, it is clear that our solar system is not a typical star system. It lacks any planets closely orbiting the central star and any superearth-sized worlds, amongst other things. Still, a full picture of a typical star system or even accurate inventories of extrasolar planets are limited by the tools currently available: mostly orbital doppler effects and transits, both of which favour the detection of closely orbiting and/or massive worlds. Those few worlds directly imaged are mostly large young (and therefore hot) super-jovian planets. These attempts to create a model from current information will probably look naïve or just plain wrong in a few decades time when better information becomes available. To repeat an adage: all models are wrong; some models are useful. Hopefully these are useful.

Still, a goal of this effort has been to try to bridge existing Traveller material and decades of accumulated Traveller lore (much of which has a home on the wiki) with what is currently known about star systems and planets. To that end, this book keeps a modified form of the Orbit# system, even though it was originally based on the Titus-Bode relationship, a formula that has no scientific basis and does not exactly work, even for Neptune. The major modification to the Orbit# system was to set the base of Orbit# 0 at 0.0 AU, not 0.2 AU as in those previous versions and to focus on fractional Orbit# values. This allows for the many tightly packed systems such as TRAPPIST-1 (whose seventh known planet is only 0.06 AU from its star) to be modelled. Retaining Orbit#s also has the advantage of providing a simple method to continue to widen the gap between planets in a way that keeps the ratio of their periods more or less intact. It also works well enough for initially determining distances between stars in a multi-star system using the T5 Close, Near, Far star paradigm. Adding fractional Orbit#s is something that has already crept into other Traveller publications and its extensive use here just expands upon it.

The principle (a generic statement which may turn out to be incorrect) that planets are as densely packed as possible led to the concept of spread, which allows for both densely and sparsely packed systems while still keeping some sort of period-based ratio – a very modified Titus-Bode.

Rules for available Orbits# in multi-star systems are simplified and based on these arbitrary Orbit#s, not actual orbital mechanics. An initial attempt to model this based on stellar mass, orbits, and eccentricity was quickly abandoned once I realised that I was trying to solve a three (or more) body with spreadsheet math. Astronomers and physicists may cringe at the result, but it is close enough for game use, and a Referee is always free to move an offending Orbit# to another location. Likewise, the true hierarchical view of a multi-star system with barycentres and such was abandoned for a primary-centric Orbit# view. Again, good enough for game use, and a large number of calculations will in most cases likely result in outcomes similar to the rules of thumb presented here.

Temperatures, for all the complexity presented here are much more complex than modelled in this book. An often cited dozen-page paper on ‘simplified’ determination of temperature by latitude would have resulted in a full page of explanation and calculation, followed by frustration. The approximations in the book at least provide plausible results.

Still, it is possible that I have made some fundamental mistakes and that reviewers and editors will not catch them. For that, I apologise in advance.

Finally, as mentioned in the introduction, this book is intended as a guide, not a straitjacket. The rules could allow a Referee to create a programmatic method to generate star systems. I have done so by other methods in the past and tested the results of this book’s procedures in an overly complex yet inadequate spreadsheet form. And while that might be suitable for an exploration campaign such as Deepnight Revelation, it is not as suitable for the continuation method, especially in an existing campaign. Worse, it removes Referee creativity from the process. While rules for determining the length of a year or the basic temperature are physics-based, the Referee could and should move worlds around, adjust greenhouse and albedo values or change atmospheric gas mixes if that is what makes a world match their vision.

The game belongs to the players, not the dice.
 
What a comprehensive and pro-active update - thanks

Something workable is preferable to something esoteric requiring a high degree of domain knowledge
 
Can't wait to see it! I really want to know how the binary star systems are handled.
 
Can't wait to see it! I really want to know how the binary star systems are handled.
You may not like it.
As it says above, I chose to follow the model from T5 (Primary, Close, Near Far, each with a possible Companion), which is centred (yes, I meant to spell that word that way - it's British even if it looks 'wrong') on the main (most massive) Primary star, not barycentres. I tried to do it the 'correct' way, but it's too complex to model without way more math than is already in there - especially if you add eccentricity to the orbits. A modified T5 method retains compatibility all the way back to Classic Traveller. And few system have more than three stars in any case. In my many, many runs, I never got more than seven (ignoring various modifiers, you'd need 6^7 or 279,936 systems to hit eight stars - didn't run more than 10% of that through a only partially functional 100MB spreadsheet model...) .
 
You may not like it.
As it says above, I chose to follow the model from T5 (Primary, Close, Near Far, each with a possible Companion), which is centred (yes, I meant to spell that word that way - it's British even if it looks 'wrong') on the main (most massive) Primary star, not barycentres. I tried to do it the 'correct' way, but it's too complex to model without way more math than is already in there - especially if you add eccentricity to the orbits. A modified T5 method retains compatibility all the way back to Classic Traveller. And few system have more than three stars in any case. In my many, many runs, I never got more than seven (ignoring various modifiers, you'd need 6^7 or 279,936 systems to hit eight stars - didn't run more than 10% of that through a only partially functional 100MB spreadsheet model...) .
Personally I don't care too much if the system is not completely astronomically correct, it's just a game after all. It needs to be beleivable and provide fairly realistic results but, more importantly, needs to be quick and painless getting the results.
 
Personally I don't care too much if the system is not completely astronomically correct, it's just a game after all. It needs to be beleivable and provide fairly realistic results but, more importantly, needs to be quick and painless getting the results.
The pain level depends on the amount of detail you want. I mention MOARN (Map Only As Really Necessary) - also taken from T5. I only did full systems to see if the dice rolls worked. I don't recommend doing complete detailed systems. And I didn't even do even complete full systems - for performance reasons I had to cap the the moon count at 6 per planet for my convoluted spreadsheet - only an issue for gas giants, but still. There's plenty of complicated formulas for temperature, but you can also just base the temperate on the world's deviation from the central habitable zone and an atmosphere DM and skip all that thermodynamics, reflectivity and greenhouse figuring.

The idea is to build tools to use - or at least do the research for you to provide certain formulas and their effects - with a choice on how much detail you want. There' a whole text box on how to calculate the number of hours of daylight based on season (axial tilt and time of local year) and latitude (and rotation rate), but it's only there because I wanted to know how to do it, and it might matter if the referee wants to be particular for certain adventure-relevant reasons and it took half a day of Google to figure out the answer and try to explain it. So there it is, if you want it and if it's really necessary.
 
You may not like it.
As it says above, I chose to follow the model from T5 (Primary, Close, Near Far, each with a possible Companion), which is centred (yes, I meant to spell that word that way - it's British even if it looks 'wrong') on the main (most massive) Primary star, not barycentres. I tried to do it the 'correct' way, but it's too complex to model without way more math than is already in there - especially if you add eccentricity to the orbits. A modified T5 method retains compatibility all the way back to Classic Traveller. And few system have more than three stars in any case. In my many, many runs, I never got more than seven (ignoring various modifiers, you'd need 6^7 or 279,936 systems to hit eight stars - didn't run more than 10% of that through a only partially functional 100MB spreadsheet model...) .
I don't see why I would dislike it. Lots of the worlds on travellermap have binary stars like https://wiki.travellerrpg.com/Lakamsal_(world).
I would like to see how it meshes with that.
 
I tried to do it the 'correct' way, but it's too complex to model without way more math than is already in there - especially if you add eccentricity to the orbits.
Revisiting this discussion again, it is not 'correct' to try to model something that we do not have an agreed theory for at this point; unless you are actually in the business (astronomy) of doing so precisely so you can test it against observations.

Emulating known (and assumed) observations is the correct approach and the one that Traveller has already used, wisely.
 
Hah, beat me to it.

This is all definitely a moving target and I’m glad Geir seems to be putting playability ahead of stark simulation.
 
Copying in some (hopefully relevant) things from the text for you all :)

'At least as of the early 2020s, our solar system appears to be an outlier, not a standard. Forty years further into the future, much of what follows, at least on the physical proprieties of star systems and worlds, will likely be proven incorrect or at least incomplete, but this book will attempt to bring the process of star system generation and physical world development in line with current knowledge.'

'While the book provides formulas and tables compatible with known states of sciences, physical, social, economic, and technological, they do not represent a comprehensive review of any discipline. They are designed to be workable rules for developing details in the Traveller universe.'


I recognise my bias, but it is an interesting book, and not overly hard to follow. Hope these sections help with clarity, too.
 
Hah, beat me to it.

This is all definitely a moving target and I’m glad Geir seems to be putting playability ahead of stark simulation.
And I'm even slower. Distracted. Didn't see the article until my morning.

Yeah, I put in the 'rule' of inside the Roche limit: ring. Outside the limit: moon.
But even that rule is based on simplified computations, as different materials will have different Roche limits (steel moon ball = much closer than than squishy, half-void rubble pile). But simplified rule is what I went for. And even in the case we don't know much beyond early observations : could be a recent collision (takes a while to form a moon) or could be kept from coalescing by some resonance from the moon Weywot (brain wants to write Wynona for some reason - brain broken).

Anyway. Rules, unless they break physics badly, are just 'guidelines'. And even when they break physics (Deneb with intelligent natives around a star less than 5 million years old), there's always the Ancients, Alien Space Bats (are they related to Ancients?), or Elder Gods to explain something away. Science Fiction, after all.
 
Very eagerly waiting for this release. There's no such thing as absolute accuracy here and even no need for it as we're talking about an RPG supplement. It's important to strive for scientific accuracy of course, but a workable set of rules which provide plausible (enough to suspend disbelief) results is more than enough.

By the way, there are already theories about the ring system quoted above. Here's a link to one: https://www.nature.com/articles/s41586-022-05629-6 Unfortunately it is behind a paywall, but the abstract is free. The relevant bit: "The detected ring orbits at 7.4 radii from the central body, which is well outside Quaoar’s classical Roche limit, thus indicating that this limit does not always determine where ring material can survive. Our local collisional simulations show that elastic collisions, based on laboratory experiments, can maintain a ring far away from the body. Moreover, Quaoar’s ring orbits close to the 1/3 spin–orbit resonance with Quaoar, a property shared by Chariklo’s and Haumea’s rings, suggesting that this resonance plays a key role in ring confinement for small bodies."
 
I am just going to ask if this book comes out, that there is at least an idea of what Xenobiologicals could exist or even some basic rules how to create thing so that we might have a chance to have players land on a planet and maybe worry about the plant life or the animal life maybe a threat or maybe become a trade item. At least make the planet feel "alive" and not something that is just a rock in space.
 
There's a biocomplexity rating, from simple single celled organisms (like prokaryotes) to "Ecosystem-wide superorganisms" but other than some generic earthlike examples, no particular details.

It's probably worth a whole book to do ecosystems right - flora, fauna, things in-between or neither, with some rules on design based on environment - not another 'Animal Encounters' (Classic Supplement 2 and MgT v1 Supplement 11), but something to build a native ecosystem. And perhaps deal with mixed ecosystems - in The Third Imperium, there's 300K years of Ancients interference and consequences, 10K years of Vilani imported invasive species, and 3K years of Solomani imports and geneering. And then a bunch of tables for those who just want something quick and easy.

Existing, but hardly sufficient is a table I put in the Sector Construction Guide dealing with sophont physical characteristics (p.51 if you have it). That table is more 'prompts' to to stimulate Referee imagination than any sort of design system.
 
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