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
-**Current:** RK4 (Runge-Kutta 4th order) integration
-**Proposed:** Newton-Raphson propagation for higher precision
+### Newton-Raphson Analytical Propagation
+**Current:** RK4 (Runge-Kutta 4th order) numerical integration
+**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
-- Better handling of near-parabolic trajectories
-
-**Implementation Considerations:**
-- May require adaptive timestep sizing
-- More complex than RK4
-- Trade-off between accuracy and performance
-
-### Io and Titan Orbital Stability Tuning
-**Issue:** Outer solar system moons exhibit orbital drift
-
-**Approaches:**
-- Reduced timestep for moon systems
-- Specialized local frame handling
-- Higher precision for distant parent-body interactions
-- Moon-specific integration parameters
-
-**Validation:**
-- Long-term stability tests (> 100 orbits)
-- Energy conservation metrics
-- Orbital period accuracy verification
+- Time steps of hours/days (vs. seconds/minutes with RK4)
+- 60-2880x performance improvement depending on orbit scale
+- Perfect 2-body accuracy with no numerical drift
+- Newton-Raphson converges in 3-5 iterations
+
+**Implementation Approach:**
+- Analytical propagation for orbital motion (99% of simulation time)
+- RK4 integration during finite-duration burns (1% of time)
+- Seamless transitions between modes
+- SOI transitions with orbital element transformations
+
+**Estimated Effort:** 30-44 hours across 5 implementation phases
+
+### Orbital Stability Validation
+**Status:** Time step stability analysis complete
+
+**Findings (from `tests/informational/test_time_step_stability`):**
+- RK4 at 60s is very stable (22% of stability limit)
+- Mercury orbiter (MESSENGER-like) is limiting factor: 270s max stable dt
+- Io and Moon are very stable (>596s max stable dt)
+- 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