# Refactor Orbital Elements Session (2026-01-04)

## Changes Made

Refactored orbital elements calculation from test-specific to reusable code:
- Moved `OrbitalElements` struct from test file to `src/simulation.h`
- Moved `calculate_orbital_elements()` function to `src/simulation.cpp`
- Created `tests/test_comet_orbit.cpp` with SOI transition tracking
- Added `ParentChange` tracking to detect when comet switches gravitational parent
- Removed `tests/test_soi_transitions.cpp` (not useful for detecting actual transitions)
- Updated Makefile to include new test file

## Commits

- `0e2f9dd` Refactor orbital elements to reusable code and track SOI transitions

## Results

4 files changed, +225/-1 (net +224 lines)

Orbital elements calculation is now reusable across the codebase. Test properly tracks parent index changes, though current configuration shows comet misses Mars's SOI by ~0.0004 AU (likely due to 60s time step granularity).

## Outstanding Issue

Test fails to reproduce manual debugging results. Manual debugging showed `parent_index` changing to 2 (Mars) at sim->time ≈ 133914000s (~1550 days), but automated test detects no parent changes. Closest approach in test: 0.004200 AU, Mars SOI: ~0.00379 AU. Discrepancy may be due to time step granularity (60s), different initial conditions, or timing of SOI calculations. Requires further investigation.