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.
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.
