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docs/session_summaries/2026-02-04-analytical-propagation.md

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+# 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