Now that I’ve got the Realistic Near Star Map Project out of the way I thought I’d take a look at the world generation system from the original GDW 2300AD Directors Guide, which I haven’t really examined in detail before. To do this, I automated the generation system so that I could generate thousands of systems and go over the statistics of the results.
However, I had to make a few tweaks to the system while writing the program so it’s not entirely faithful to the original system in the Directors Guide. First, the 2300AD system was designed to be used with existing stars, so I had to add a stellar generation system to generate those on the fly. I used a slightly modified version of my Revised Stellar Generation Tables (the original is available on my Worldbuilding page), that only generated solo stars (largely because it was easier to program that way). I used the stellar data tables from 2300AD to determine the stars’ luminosity and radius, but I just used the mass from the “V” column since in reality stars don’t change their masses significantly when they evolve into sizes II, III and IV. I also assumed fixed masses for the II and III Giants (1.5 Ms) and the White Dwarfs (0.5 Ms).
Another issue was that 2300AD is missing an Orbital Zone – there is a gap between the outer edge of the Habitable Zone and the inner edge of the Outer Zone. This “Middle Zone” is where Mars is located in our own Solar System, and cold rocky bodies (as opposed to icy bodies) would dominate there.
Additionally, in the original system, Gas Giants could snowball to immense sizes – the radius multiplier could go up to 16x the original rolled radius, which meant that you could potentially get Gas Giants with a radius of up to 384,000 km – over half the size of Sol! Obviously, this is not realistic – in reality, the maximum radii of jovians (that aren’t in star-hugging “Torch orbits”, at least) is between 70,000 and 80,000 km, because at that point adding more mass just causes them to self-compress further. In other words, Jupiter is about as big as a Gas Giant can get in terms of radius, though more mass can be piled into it and it wouldn’t get much bigger. So I set the upper limit at 70,000 – 80,000 km here, which results in an upper mass limit of about 8 Jupiter Masses (still too small for a Brown Dwarf though).
Finally, I simply calculated the MMW (and blackbody temperature and mass) of each planet instead of attempting to encode the tables directly. The MMW table in the book isn’t accurate in a general case anyway – this is discussed further in the Observations section.
Aside from these changes, I was able to translate the worldgen rules pretty faithfully into the program. Once that was done, I could set up runs that would generate 100,000 systems to investigate how many of which types of stars and worlds were created.