Remove [!mayfail] tags from now-passing inclined orbit tests

- Molniya position tests now pass with 3D rotation implementation
- Generic inclined orbit test passes with proper argument_of_periapsis
- Only orbital period test still fails (orbit tracker needs 3D fix)
- Add plan document for fixing update_orbit_tracker()

docs/planning/orbit-tracker-3d-fix-plan.md

@@ -0,0 +1,78 @@
+# OrbitTracker 3D Fix Plan
+
+## Problem
+`update_orbit_tracker()` only uses `atan2(y, x)` which calculates the angle in the x-y plane. For 3D inclined orbits, this doesn't track the true orbital angular position because:
+1. The spacecraft moves in an inclined orbital plane (not the x-y plane)
+2. The x-y projection doesn't represent the true angular progress around the orbit
+
+## Current Implementation (Failing)
+```cpp
+Vec3 relative_pos = vec3_sub(body->global_position, parent->global_position);
+double current_angle = atan2(relative_pos.y, relative_pos.x);  // Only works for 2D orbits in x-y plane
+```
+
+## Solution
+Track the orbital angular position by projecting the 3D position onto the orbital plane and calculating the true anomaly.
+
+## Implementation Approach
+
+### Option 1: Store Orbital Plane Normal (Recommended)
+Add fields to `OrbitTracker` to store the orbital plane orientation:
+- `Vec3 orbital_plane_normal` - Normal vector to the orbital plane
+- `Vec3 reference_direction` - Reference direction in the orbital plane (periapsis direction)
+
+Calculation steps:
+1. Compute orbital plane normal from inclination (i) and RAAN (Ω):
+   ```
+   n_x = sin(i) * sin(Ω)
+   n_y = -sin(i) * cos(Ω)
+   n_z = cos(i)
+   ```
+
+2. Compute periapsis direction in 3D space:
+   ```
+   R_z(Ω) · R_x(i) · R_z(ω) transforms (1, 0, 0) to periapsis direction
+   ```
+
+3. Project position onto orbital plane and calculate angle from periapsis
+
+### Option 2: Use Existing Rotation Matrix
+Reuse `mat3_rotation_orbital()` to transform position back to orbital plane coordinates:
+
+1. Apply inverse rotation: `R_orbital^T · r_3D = r_orbital_plane`
+2. Calculate angle in orbital plane: `atan2(y_orbital, x_orbital)`
+
+This is simpler and reuses existing code.
+
+## Changes Required
+
+### test_utilities.h
+- Add `double inclination` field to `OrbitTracker` struct
+- Add `double longitude_of_ascending_node` field
+- Add `double argument_of_periapsis` field
+
+### test_utilities.cpp
+- Modify `create_orbit_tracker_with_min_time()` to accept orbital elements
+- Modify `update_orbit_tracker()` to:
+  1. Build inverse rotation matrix from stored orbital elements
+  2. Transform 3D position back to orbital plane
+  3. Calculate angle in orbital plane
+
+### test_inclined_orbits.cpp
+- Update `create_orbit_tracker_with_min_time()` calls to pass orbital elements
+
+## Test
+- Molniya orbital period test should pass (12 hours ± tolerance)
+- All other orbit tests should continue to pass
+
+## Notes
+- Backward compatibility: Planar orbits (i=0) should work exactly as before
+- The inverse rotation is just the transpose of the rotation matrix (orthogonal)
+- Performance: Minimal impact, only called during tests
+
+## Files to Modify
+1. `src/test_utilities.h` - Add orbital element fields to OrbitTracker
+2. `src/test_utilities.cpp` - Implement 3D angle calculation
+3. `tests/test_inclined_orbits.cpp` - Update tracker creation calls
+4. `tests/test_orbital_period.cpp` - May need updates if using tracker
+5. `tests/test_moon_orbits.cpp` - May need updates if using tracker

tests/test_inclined_orbits.cpp

@@ -9,7 +9,7 @@
 const double POSITION_TOLERANCE_METERS = 10000.0;
 const double PERIOD_TOLERANCE_SECONDS = 600.0;
 
-TEST_CASE("Molniya orbit - position verification at multiple true anomalies", "[inclined][molniya][!mayfail]") {
+TEST_CASE("Molniya orbit - position verification at multiple true anomalies", "[inclined][molniya]") {
     const double TIME_STEP = 60.0;
     const double SECONDS_PER_DAY = 86400.0;
     const double SEMI_MAJOR_AXIS = 26540000.0;
@@ -138,7 +138,7 @@ TEST_CASE("Molniya orbit - orbital period verification", "[inclined][molniya][pe
     destroy_simulation(sim);
 }
 
-TEST_CASE("Generic inclined orbit - moderate inclination", "[inclined][generic][!mayfail]") {
+TEST_CASE("Generic inclined orbit - moderate inclination", "[inclined][generic]") {
     const double TIME_STEP = 60.0;
     const double SEMI_MAJOR_AXIS = 10000000.0;
     const double ECCENTRICITY = 0.5;