update mission_planning doc with manual debugging notes

docs/mission_planning.md

@@ -122,6 +122,17 @@ Add Spacecraft body to config with placeholder position/velocity (set at runtime
 
 ### Problem: Incorrect Delta-V Direction After Multi-Day Wait
 
+FIXME: while running this simulation config graphically, I noticed that a larger
+    problem is in simulation::find_dominant_body(). Earth's parent gets set to
+    the satellite's index, which should never happen.
+    I think the actual fix should be to have non-massive satellites in a different
+        array than celestial bodies, and treat them differently.
+    However, we should add more testint for the case that a comet or other massive
+        celestial body gets close to another body.
+    We do have tests/test_soi_transition.cpp, and tests/configs/soi_transition.toml
+        so maybe it's an initialization problem because the new test config starts
+        with both bodies in each others SOI?
+
 **Symptom:**
 - Spacecraft enters LEO orbit correctly with negative energy (bound to Earth)
 - Waits 94 days for Earth-Mars launch window