Planetary Systems

How planetary systems are defined in MTU

Building out a planetary system

A while ago I started looking at automation for building planetary systems. The supplement that had always drawn my attention in the past was the MegaTraveller World Builder's Handbook[1] as it extended the previous system builds into an larger version. However, rolling up a system could take hours, sometimes longer! For hand rolling systems it really is MOARN. I enjoy programming/scripting, so even though there were a few websites out there that provided some system mapping, I wrote my own, mainly so that I could customise where I wanted. I included some elements from the Traveller New Era's World Tamer's Handbook[1], around land masses and continents and even some ideas from the GURPS Traveller First In[1] book.

Since I built the script there have been further tools and books available, such as the excellent website at Traveller Worlds[2], and I joined the Patreon for Jon F. Zeigler's (of GURPS First In fame) new book, Architect of Worlds[2]. Mongoose has also released their new version of the World Builder's Handbook[2]. All of these will influence me into rewriting what I already have, but I've also been researching more and more into astrophysics in general and will likely follow Jon F. Zeigler's route in making a new generator based on some of the current up-to-date research.

The script itself takes input of a system name, such as 'Kinorb' and a hex and/or sector if required (as there are more than one system's called 'Kinorb') and then uses the Traveller 5 Second Survey data as the starting point to build the system. Some defaults can be supplied if there are canon references to how a system should turn out. Through the mechanics and random elements the system is built and a (huge) JSON file is created with the data. An overview of this is supplied for general reference and looks like the below.

System Generation output for Kinorb
System Generation output for Kinorb (Screenshot)

Alongside this is included some basic information about the homeworld.

System Generation homeworld information for Kinorb
System Generation homeworld information for Kinorb (Screenshot)

The created JSON file is much more detailed and contains similar information for every body, using the random generation rules as noted earlier. The random generation is based upon a seed (which defaults to the system's name and given details) so that the same result is always returned when required.

An Imperial date and time can be supplied to the script which then gives a view of where all of the bodies are in their orbits and allows a general system map to be produced as well as a view of how large objects would be in the sky if you were stood at the meridian/equator on the homeworld (a reference view) and then also provide for the date and time what objects are in the sky right now.

System Generation System Map
System Generation System Map (Generated PNG)
System Generation Size Comparison
System Generation Size Comparison (Generated PNG)

In the above we can see the very different apparent sizes of the two moons of Kinorb. Although they are of a similar size (both Size 1), one of them is very close and would appear huge in the sky compared to our moon. The other is quite some distance away and would be a small bright dot. All of this information can be used to help build out the homeworld and system with stories and interesting facts if needed.

References

System Generation Script

[1] Many of the calculations and random elements in the basic system generation scripts are from:

  1. Fugate, Joe, Keith, J. Andrew, Thomas, Gary L. — World Builder's Handbook (Digest Group Publications, 1989)
  2. McInnes, Terry and Nilsen, David — World Tamer's Handbook (Game Designers' Workshop, 1994)
  3. Zeigler, Jon F. — First In (Steve Jackson Games, 1999)

[2] Later books and websites that have influenced me and might force a rewrite are:

  1. Sherlock, Jonathan A. — Traveller Worlds
  2. Zeigler, Jon F. — Architect of Worlds (Ad Astra Games, 2024)
  3. Lanesskog, Geir — World Builder's Handbook (Mongoose Publishing, 2023)