Not particularly intending to resurrect this "dead thread", but it turned up when I was looking for something else. But in case someone else comes across this, while in the position of thinking about position systems ...
Fronclynne here has a fundamental error in his understanding of celestial dynamics :
fronclynne wrote: ↑Thu Nov 08, 2012 5:05 pm
If you assume that the witchpoint, sun, & planet are all in the plane of the ecliptic (but this assumes that the sun doesn't rotate, which I guess may well be in Oolite) the display of your cardinal points should be possible without having to set arbitrary beacons (though not necessarily trivial).
Aslo, in the framework of a (hypothetically) revolving system would there be some better system than Euclid's?
The rotation state of a star isn't, fundamentally, strongly related to the star systems "fundamental plane" - which in itself isn't well defined. Terrestrial celestial mechanics refers everything to the plane of the Earth's orbit around the Sun, which is, coincidentally not that different to the orbital planes of the other planets (degrees inclination : Me 7, V 3.4, E 0 [Moon 5.1], Ma 1.9, Ju 1.3, Sa 2.5, U 0.8, N 1.8, then the small stuff is, literally, "scattered"), but as we've gained understanding of exoplanet systems, we see a lot more variation in inclination, including several cases where some planets orbit in a direction
retrograde to other planets in the same system. People have even worked out sane-sounding ways to evolve from a rational-sounding "everything developed from a debris cloud collapsing onto one plane of angular momentum" model of planet formation, through sane (-ish) sounding interactions, to end up with one retrograde planet (i.e orbital inclination between 90 and 180 degrees to the rest of the system). Truly, the universe is weirder than we expected. Or in the vernacular, "who ordered
that?"
So, if someone is rationally designing a planet system (or setting parameters for a random-system generation), the sane way to go would be to put everything orbiting normally, close to one plane, but if you want to throw in a curve retrograde ball every so often, that's within the bounds of our Universe. The betting money would go for having most big stuff (planets, gas giants in particular) close to one plane, and the small stuff (asteroids, comets) much more randomly distributed. But that's definitely not a hard restriction. There's even one real system with a major planet inclined at about 90 degrees to everything else - which sounds like a recipe for wild interactions and eventual impacts. But it seems to be stable. Well, stable enough for us to find it in the first 5000-odd examples.
On defining "available in every system (that would appear in the Ooniverse)" points for some absolute position frame, I'd throw in these three "fixed" points for the compass to identify : The star (doh, but in the event that someone builds a binary or higher system, the MOST MASSIVE star) as the zero point for the coordinate system. The
administrative capital planet of the system (allowing for multiple inhabited planets in one system) to define the "X" axis (which technically makes this a coordinate system that is co-rotating with the administrative planet - make up your own justifications for that). Then to define the system's "fundamental plane", identify the trailing Lagrangian point in the star-administrative capital system, which in polar coordinates would be at point r=1 "AU", theta=(minus)60 "degrees" and phi=0 degrees.
Does the core engine scale orbital radii to the "Prime" planet of the system - I can't remember. THeres some fudging of "km" and "Oo-astronomical Units", isn't there?
If you want to populate an unoccupied system (isn't there a system whose star went nova and destroyed the inner planets in Galaxy 4?), choose the
second largest body of the system (normally the largest gas giant, but ... binary stars!? ) as the anchor point for the reference system instead of the administrative capital.
I wonder if the core system programmers have looked at binary star systems. I'm thinking in particular of the Alpha Centauri system, where "Alpha" is a binary of two near-solar size stars separated by a distance varying (Kepler, ellipses!) by a Saturn-like spacing at perihelion and a Pluto-like spacing at aphelion. (Orbital period 79-odd years.) That allows for stable orbits for anything closer to the "A" star than about a Mars-orbit and around the "B" star ... some stable orbits, but I forget the paper details. I'll have to re-read it - which means re-finding it.. Then there is Proxima Centauri, which is a runt of a star out at about 430 time the A-B aphelion separation, but still gravitationally bound.
Maybe I should have tracked down a "core game engine" thread for this. But I'd better un-pause my passenger delivery run into Bionus. Whinging passenger is moaning about the flight time. (That happens a lot more since a recent OXP update.
That OXP is going to need to add a Bounty-style "lifeboat, bag of food, sextant and one oar" option to terminate a passenger run!