From 01ce10044e941e3569579aebcaf7f8c6672680e6 Mon Sep 17 00:00:00 2001 From: cinnaboot Date: Mon, 4 May 2026 10:42:56 -0400 Subject: [PATCH] docs: add Laplace plane data limitations and decision note --- docs/planetary_data.md | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/docs/planetary_data.md b/docs/planetary_data.md index 5dbd0b8..9f655a2 100644 --- a/docs/planetary_data.md +++ b/docs/planetary_data.md @@ -61,3 +61,15 @@ To get the true anomaly ν (which the TOML `orbit.true_anomaly` expects), solve tan(ν/2) = √((1+e)/(1−e)) · tan(E/2) Once ν is computed for each body, set it as `true_anomaly` in the config. The engine will then propagate from the J2000 snapshot forward. + +### Laplace Plane Data Limitations + +Reliable, authoritative data for the Laplace plane parameters (pole R.A./Dec. and tilt relative to each planet's equator) is difficult to find in standard planetary data sources. JPL Horizons and the JPL orbits page provide moon orbital elements relative to the Laplace plane but do not publish the Laplace plane's own orientation in ICRF. + +**Decision**: Use the planet's equatorial frame for moon orbital elements instead of converting from the Laplace plane. The Laplace plane is very close to the equatorial plane — tilted by only ~1° for Jupiter and ~0.3° for Saturn — so the resulting errors are negligible: + +- Inclination offset: ~0.3–1° +- Node and periapsis offset: similar small amounts +- Angular position error in space: ~0.3–1° + +This error is smaller than the uncertainties from using mean orbital elements (which ignore perturbations and resonances) and has no practical impact for simulation purposes.