Update future work doc - reference Newton-Raphson plan and stability findings

docs/future_work.md

@@ -26,32 +26,38 @@ This document outlines planned enhancements and future development areas for the
 - Add validation tests for energy/momentum conservation
 - Consider relative velocity of parent bodies
 
-### More Accurate Integration Methods
+### Newton-Raphson Analytical Propagation
-**Current:** RK4 (Runge-Kutta 4th order) integration
+**Current:** RK4 (Runge-Kutta 4th order) numerical integration
-**Proposed:** Newton-Raphson propagation for higher precision
+**Proposed:** Newton-Raphson analytical propagation with hybrid burn handling
+
+**Status:** Implementation plan created - see `docs/newton_raphson_propagation_plan.md`
 
 **Benefits:**
-- Improved accuracy for long-term orbit predictions
+- Time steps of hours/days (vs. seconds/minutes with RK4)
-- Better handling of near-parabolic trajectories
+- 60-2880x performance improvement depending on orbit scale
-
+- Perfect 2-body accuracy with no numerical drift
-**Implementation Considerations:**
+- Newton-Raphson converges in 3-5 iterations
-- May require adaptive timestep sizing
+
-- More complex than RK4
+**Implementation Approach:**
-- Trade-off between accuracy and performance
+- Analytical propagation for orbital motion (99% of simulation time)
-
+- RK4 integration during finite-duration burns (1% of time)
-### Io and Titan Orbital Stability Tuning
+- Seamless transitions between modes
-**Issue:** Outer solar system moons exhibit orbital drift
+- SOI transitions with orbital element transformations
-
+
-**Approaches:**
+**Estimated Effort:** 30-44 hours across 5 implementation phases
-- Reduced timestep for moon systems
+
-- Specialized local frame handling
+### Orbital Stability Validation
-- Higher precision for distant parent-body interactions
+**Status:** Time step stability analysis complete
-- Moon-specific integration parameters
+
-
+**Findings (from `tests/informational/test_time_step_stability`):**
-**Validation:**
+- RK4 at 60s is very stable (22% of stability limit)
-- Long-term stability tests (> 100 orbits)
+- Mercury orbiter (MESSENGER-like) is limiting factor: 270s max stable dt
-- Energy conservation metrics
+- Io and Moon are very stable (>596s max stable dt)
-- Orbital period accuracy verification
+- Current default (60s) provides excellent margin
+
+**Documentation:** See `tests/informational/README.md` for test details and results
+
+**Conclusion:** No stability tuning needed - RK4 works well for moon systems with existing dt=60s default
 
 ## Visualization Enhancements