Fix terminal handling of CoastDuring burn-coast-burn

MechJeb2/MechJebModuleGuidanceController.cs

@@ -129,7 +129,7 @@ private bool WillDoRCSButNotYet()
             bool hasRCS = Vessel.hasEnabledRCSModules() &&
                 VesselState.RCSThrustAvailable.Up > 0.1 * VesselState.RCSThrustAvailable.MaxMagnitude();
 
-            return hasRCS && Status != PSGStatus.TERMINAL_RCS && Core.StageStats.VacStats.Count - 1 <= Solution.TerminalMJPhase();
+            return hasRCS && Status != PSGStatus.TERMINAL_RCS && Vessel.currentStage == Solution.TerminalKSPStage();
         }
 
         private void HandleTerminal()
@@ -150,6 +150,21 @@ private void HandleTerminal()
                 return;
             }
 
+            /*
+             * FIXME: consider liquid booster()s + unguided beehive cluster
+             *
+             * 1. we should enter terminal guidance on the top liquid booster and shut it down precisely and suspend the optimizer
+             *    there because we CANNOT use the residuals because we're about to loose our degrees of freedom.  but the optimizer should
+             *    have burned this stage to completion.  we also don't want to use TERMINAL_RCS here.
+             * 2. we should still enter terminal guidance on the top aerobee stage and precisely shut it down to actually hit the target as
+             *    best as possible, and this burntime should have been tuned by the optimizer.  we do want to use TERMINAL_RCS here.
+             *
+             * Right now we only support one OptimizeKSPStage() and really the SolutionBuilder needs to know to slap a PreciseShutdown flag
+             * onto the last liquid booster segment (even though the optimizer didn't optimize it) and likely could use the same flag for
+             * precise shutdown of engines before a coast.  Although maybe there should be two different flags (for precise shutdown with
+             * and without RCS cleanup).
+             */
+
             // this handles termination of thrust for final stages of "fixed" burntime rockets (due to residuals Tgo may go less than zero so we
             // wait for natural termination of thrust).   no support for RCS terminal trim.
             if (Solution.OptimizeKSPStage() < 0 && Vessel.currentStage <= Solution.TerminalKSPStage() && Solution.Tgo(VesselState.Time) <= 0 &&
@@ -169,26 +184,16 @@ private void HandleTerminal()
                 Status = PSGStatus.BURNING;
             }
 
-            // We should either be in an non-upper stage optimized stage, or we should be within 10 seconds of the whole
-            // burntime in order to enter terminal guidance.
-            if (Vessel.currentStage != Solution.OptimizeKSPStage() && Solution.Tgo(VesselState.Time) > 10)
+            // we need to have an optimizable stage to run terminal guidance
+            if (Vessel.currentStage != Solution.OptimizeKSPStage())
                 return;
 
-            // The includeCoast: false flag here is to skip a coast which is in the past in the Solution when
-            // we are ending the coast and the optimizer hasn't run the solution, but CoastBefore is set so
-            // that both the coast and burn have the same KSPStage.  So we want the index of the current burn
-            // and not the index of the first matching KSPStage in the Solution which is the coast.  Might
-            // also consider modifying APIs like IndexForKSPStage to omit stages which are in the past -- but
-            // I have concerns about that with residuals where you may currently be in a burning stage which
-            // is in the "past" in the Solution but you're burning down residuals and you don't know when
-            // the stage will actually run out (assuming it isn't a burn before a coast or an optimized burntime
-            // so that we burn past the end of the stage and into whatever residuals are available).
-            int solutionIndex = Solution.IndexForKSPStage(Vessel.currentStage, Core.Guidance.IsCoasting());
-            if (solutionIndex < 0)
+            // we need to be within 10 seconds of the end of the stage to run terminal guidance
+            if (Solution.TgoForKSPStage(VesselState.Time, Vessel.currentStage) > 10)
                 return;
 
-            // Only enter terminal guidance within 10 seconds of the current stage
-            if (Solution.Tgo(VesselState.Time, solutionIndex) > 10)
+            // but if we're doing a coast, or going to do a coast we don't enter terminal guidance yet
+            if (Vessel.currentStage == Solution.CoastKSPStage() && Solution.WillCoast(VesselState.Time))
                 return;
 
             if (Status != PSGStatus.TERMINAL_RCS)

MechJebLib/PSG/Solution.cs

@@ -239,6 +239,19 @@ public double Tgo(double t, int n)
             return TgoBar(tbar, n) * _timeScale;
         }
 
+        public double TgoForKSPStage(double t, int kspStage)
+        {
+            double tbar = (t - T0) / _timeScale;
+            double sum = 0;
+            for (int i = IndexForTbar(tbar); i < Phases.Count && Phases[i].KSPStage == kspStage; i++)
+            {
+                if (Phases[i].Coast)
+                    continue;
+                sum += TgoBar(tbar, i) * _timeScale;
+            }
+            return sum;
+        }
+
         public double TgoBar(double tbar, int n)
         {
             if (tbar > _tmin[n])
@@ -255,6 +268,7 @@ public bool Coast(double t)
         }
 
         // Specialized API to determine if we still have the coast in our future or not
+        // (or if we're in a coast right now)
         public bool WillCoast(double t)
         {
             double tbar = (t - T0) / _timeScale;