The final RCS ullage fix

1. the node executor will continuously apply RCS in the "lead"
   time if the vessel is aligned with the node.

2. the thrust controller will continuously apply RCS until the
   thrust of the engines exceeds the fore thrust of the RCS
   engines.

Signed-off-by: Lamont Granquist <lamont@scriptkiddie.org>

MechJeb2/MechJebModuleNodeExecutor.cs

@@ -88,8 +88,8 @@ public void Abort()
             Core.Warp.MinimumWarp();
             Core.Thrust.ThrustOff();
             Users.Clear();
-            _dvLeft = 0;
-            State   = States.IDLE;
+            _dvLeft   = 0;
+            State     = States.IDLE;
         }
 
         protected override void OnModuleEnabled()
@@ -119,15 +119,11 @@ public enum States { WARPALIGN, LEAD, BURN, IDLE }
         private        double   _ignitionUT;
         private static bool     _isLoadedPrincipia => VesselState.isLoadedPrincipia;
         private        bool     _hasNodes          => Vessel.patchedConicSolver.maneuverNodes.Count > 0;
-        private        double   _ullageUntil;
 
         public override void Drive(FlightCtrlState s) => DoRCS(s);
 
         private void DoRCS(FlightCtrlState s)
         {
-            // seconds to continue to apply RCS after ullage has settled to VeryStable
-            const double MIN_RCS_TIME = 0.50;
-
             if (State == States.BURN && RCSOnly)
             {
                 Vessel.ActionGroups.SetGroup(KSPActionGroup.RCS, true);
@@ -141,12 +137,6 @@ private void DoRCS(FlightCtrlState s)
             if (!Core.Thrust.AutoRCSUllaging)
                 return;
 
-            if (VesselState.lowestUllage >= 1.0 && VesselState.time > _ullageUntil)
-                return;
-
-            if (VesselState.lowestUllage < 1.0)
-                _ullageUntil = VesselState.time + MIN_RCS_TIME;
-
             if (!Vessel.hasEnabledRCSModules())
                 return;
 

MechJeb2/MechJebModuleThrustController.cs

@@ -225,8 +225,6 @@ public enum LimitMode
 
         private bool _tmodeChanged;
 
-        private double _ullageUntil;
-
         private PIDController _pid;
 
         public  float LastThrottle;
@@ -875,26 +873,22 @@ private static void MaxThrust(double[] x, ref double func, double[] grad, object
         /// <param name="s"></param>
         private void ProcessUllage(FlightCtrlState s)
         {
-            // seconds to continue to apply RCS after ullage has settled to VeryStable
-            const double MIN_RCS_TIME = 0.50;
-            // seconds after VeryStable to wait before applying throttle
-            const double IGNITION_DELAY = 0.10;
-
             if (!AutoRCSUllaging || s.mainThrottle <= 0F || ThrottleLimit <= 0F)
                 return;
 
             if (!Vessel.hasEnabledRCSModules())
                 return;
 
-            if (VesselState.lowestUllage >= 1.0 && VesselState.time > _ullageUntil)
-                return;
+            bool stableUllage = VesselState.lowestUllage >= 1.0;
 
-            if (VesselState.lowestUllage < 1.0)
-                _ullageUntil = VesselState.time + MIN_RCS_TIME;
+            // ullage may dramatically drop below stable (by as much as to 0.76 in a single tick) so
+            // we cannot "detect" low ullage and compensate, but must apply RCS until thrust has come
+            // up sufficiently.
+            if (stableUllage && VesselState.thrustCurrent > VesselState.rcsThrustAvailable.Up )
+                return;
 
             // limit the throttle only if we aren't already burning (don't waste ignitions)
-            // also apply RCS for IGNITION_DELAY seconds above VeryStable point.
-            if (LastThrottle <= 0 && _ullageUntil - VesselState.time < MIN_RCS_TIME - IGNITION_DELAY)
+            if (LastThrottle <= 0 && !stableUllage)
                 SetTempLimit(0.0F, LimitMode.AUTO_RCS_ULLAGE);
 
             if (!Vessel.ActionGroups[KSPActionGroup.RCS])