Thanks for trying, Fritz. That would have been good enough for my original intent, to get a ballpark figure, but now that I've actually dusted off my old books, I'm going the extra mile.
As an aside, the rigid fixed orbital distances from LBB6 and its descendents is one of the reasons I prefer First In and its much more flexible orbital distance creation.
Hans
Hi all. I'm back from vacation.
Hans, if you are interested in planetary orbit spacing and want a fresh perspective, you would do well to look at Rubčić and Rubčić 2010:
http://fizika.phy.hr/fizika_a/av10/a19p133.pdf
They are proposing a quantization law for planetary orbits. So far as I can tell they've been universally ignored by the astronomical community. I can see why: I'm just a biologist, and I can see things in it that make me think their reasoning is flawed. Nevertheless, it is remarkably useful for gaming purposes. It is possible to derive from their paper a simple formula for orbital spacing, and you can find a reasonably good fit using their equations for most known real-universe planetary systems. It's more complex than the Titius-Bode equation, but not daunting. It lends itself well to randomly generating realistic-looking planetary systems.
Here's the Reader's Digest version: Every planetary system has an integer packing constant K, the inverse square of which describes the "tightness" (higher numbers mean closer spacing). Actual orbits will fall at or near the square of another series of integers. The basic spacing for the system is directly proportional to the star's mass.
Taking Sol as an example:
The fundamental orbit size is 1.545 * M(star) AU (which is just 1.545 AU for Sol).
Sol's empirically observed packing constant K is 6. The inverse square is 1/36.
Orbits scale as (1.545/36) times N^2, where N is the integer number of the orbit.
Mercury is at N=3, Venus is at N=4, Earth is at N=5. Orbits 1 and 2 are empty. Some of the higher numbers are skipped as you move out past the asteroid belt. As an empirical observation, this is because the ratio of any two adjacent real-world orbits O(n+1)/O
almost always falls between the square root of 2 and 2 (probably for reasons of dynamic stability); you can see from that that certain sequences of integers will be disallowed in the Rubčić series, and that for numbers above N=7 there are multiple solutions that fall within these boundaries (note that this property makes it especially easy to generate natural-looking variety in randomly generated planetary systems if you want to go this route).
Earth's theoretical orbit is at (1.545/36) * 25 AU, or 1.073 AU. Actual orbits vary from the theoretical ones about as much as the Titius-Bode orbits do, usually within 5% but occasionally up to 10%.
It's not as cookie-cutter as Titius-Bode, and it gives good-looking results. For gaming purposes, it's easy to simulate a system using random numbers and you can vary the packing constant to account for all those epistellar jovian planets (packing constants in the range of 10 to 15 or even higher in extreme cases).
), including the interaction of the Reginan day and calendar with the Galactic Standard day and the Imperial calendar. But both I and my players found it a lot of bother to keep track of for far too little gain. 
