# Session Summary: Analytical Propagation Implementation

**Date:** 2026-02-04

## Changes Made

### 1. Implemented analytical propagation for all orbit types
- Modified `update_spacecraft_physics()` and `update_bodies_physics()` in `src/simulation.cpp`
- Replaced RK4 numerical integration with `propagate_orbital_elements()`
- Supports circular, elliptical, parabolic, and hyperbolic orbits

### 2. Fixed three critical bugs in hyperbolic orbit propagation (src/orbital_mechanics.cpp)
- `true_anomaly_to_hyperbolic()` - wrong formula (multiply vs divide, incorrect variable naming)
- `hyperbolic_to_true_anomaly()` - wrong formula (atanh vs atan, inverted factor)
- `propagate_orbital_elements()` hyperbolic case - only 1 Newton-Raphson iteration (now iterates to convergence)

### 3. Added orbital element reconstruction
- After burns in `execute_maneuver()` (`src/maneuver.cpp`)
- After SOI transitions in `update_bodies_physics()` (`src/simulation.cpp`)
- Updated `execute_maneuver()` signature to include `SimulationState*` parameter

### 4. Removed dead code
- Removed unused `solve_kepler_hyperbolic_with_prev()` function from codebase

## Commits
- Commit 1: `31f38b9` - "Implement analytical propagation for all orbit types" (6 files, +129/-15)
- Commit 2: `ec064a2` - "Remove unused solve_kepler_hyperbolic_with_prev() function" (2 files, -19)

## Results
- All 132 tests passing (240,294 assertions)
- Zero energy drift for all analytically propagated orbits
- All orbit types (circular, elliptical, parabolic, hyperbolic) now use unified analytical propagation
- Net line count: +129 -15 -19 = +95 lines

## Remaining Issues
None

## Next Steps
- Rewrite technical_reference.md from scratch to reflect current state of codebase