David Culp: Here are small changes that allow one to set a life-span for submodels.

src/AIModel/AIBallistic.cxx

@@ -32,6 +32,7 @@ FGAIBallistic::FGAIBallistic(FGAIManager* mgr) {
     _type_str = "ballistic";
     _otype = otBallistic;
     drag_area = 0.007;
+    life_timer = 0.0;
 }
 
 FGAIBallistic::~FGAIBallistic() {
@@ -79,8 +80,15 @@ void FGAIBallistic::setDragArea(double a) {
    drag_area = a;
 }
 
+void FGAIBallistic::setLife(double seconds) {
+   life = seconds;
+}
+
 void FGAIBallistic::Run(double dt) {
 
+   life_timer += dt;
+   if (life_timer > life) setDie(true); 
+
    double speed_north_deg_sec;
    double speed_east_deg_sec;
 

src/AIModel/AIBallistic.hxx

@@ -40,6 +40,7 @@ public:
     void setElevation( double el );
     void setStabilization( bool val );
     void setDragArea( double a );
+    void setLife( double seconds );
 
 private:
 
@@ -48,6 +49,7 @@ private:
     double hs;              // horizontal speed (fps)
     bool aero_stabilized;   // if true, object will point where it's going
     double drag_area;       // equivalent drag area in ft2
+    double life_timer;      // seconds
     void Run(double dt);
 };
 

src/AIModel/AIBase.cxx

@@ -51,6 +51,7 @@ FGAIBase::FGAIBase() {
     in_range = false;
     invisible = true;
     no_roll = true;
+    life = 900;
     model_path = "";
     model = 0;
     _otype = otNull;

src/AIModel/AIBase.hxx

@@ -108,6 +108,7 @@ protected:
     int id;
     bool invisible;
     bool no_roll;
+    double life;
     FGAIFlightPlan *fp;
 
     void Transform();

src/AIModel/AIManager.cxx

@@ -253,7 +253,7 @@ int FGAIManager::createShip( string path, FGAIFlightPlan* flightplan ) {
 
 int FGAIManager::createBallistic( string path, double latitude, double longitude,
                                   double altitude, double azimuth, double elevation,
-                                  double speed, double eda ) {
+                                  double speed, double eda, double life ) {
 
         FGAIBallistic* ai_ballistic = new FGAIBallistic(this);
         ai_list.push_back(ai_ballistic);
@@ -267,6 +267,7 @@ int FGAIManager::createBallistic( string path, double latitude, double longitude
         ai_ballistic->setLongitude(longitude);
         ai_ballistic->setLatitude(latitude);
         ai_ballistic->setDragArea(eda);
+        ai_ballistic->setLife(life);
         ai_ballistic->init();
         ai_ballistic->bind();
         return ai_ballistic->getID();
@@ -384,7 +385,7 @@ void FGAIManager::processScenario( string filename ) {
       } else if (en->aitype == "ballistic"){
         createBallistic( en->model_path, en->latitude, en->longitude,
                          en->altitude, en->azimuth, en->elevation, en->speed,
-                         en->eda );
+                         en->eda, en->life );
       }      
     }
   }

src/AIModel/AIManager.hxx

@@ -98,7 +98,8 @@ public:
                          double azimuth,    // in degrees (same as heading)
                          double elevation,  // in degrees (same as pitch)
                          double speed,      // in feet per second
-                         double eda );      // equivalent drag area, ft2
+                         double eda,        // equivalent drag area, ft2
+                         double life );     // life span in seconds
 
     int createStorm( string path,        // path to exterior model
                      double latitude,    // in degrees -90 to 90

src/AIModel/AIScenario.cxx

@@ -70,6 +70,7 @@ FGAIScenario::FGAIScenario(string filename)
      en->strength       = entry_node->getDoubleValue("strength-fps", 0.0);
      en->diameter       = entry_node->getDoubleValue("diameter-ft", 0.0);
      en->eda            = entry_node->getDoubleValue("eda", 0.007);
+     en->life           = entry_node->getDoubleValue("life", 900.0); 
    }
 
   entry_iterator = entries.begin();

src/AIModel/AIScenario.hxx

@@ -49,6 +49,7 @@ public:
    double strength;     // used by thermal objects
    double diameter;     // used by thermal objects
    double eda;          // used by ballistic objects
+   double life;         // life span in seconds
   } entry;
 
    FGAIScenario(string filename);

src/Systems/submodel.cxx

@@ -88,7 +88,7 @@ SubmodelSystem::release (submodel* sm, double dt)
 
   //cout << "Creating a submodel." << endl; 
   int rval = ai->createBallistic( sm->model, IC.lat, IC.lon, IC.alt, IC.azimuth,
-                                  IC.elevation, IC.speed, sm->drag_area );
+                                  IC.elevation, IC.speed, sm->drag_area, sm->life );
   //cout << "Submodel created." << endl;
   (sm->count)--; 
 
@@ -136,6 +136,7 @@ SubmodelSystem::load ()
      sm->yaw_offset     = entry_node->getDoubleValue("yaw-offset", 0.0); 
      sm->pitch_offset   = entry_node->getDoubleValue("pitch-offset", 0.0);
      sm->drag_area      = entry_node->getDoubleValue("eda", 0.007);
+     sm->life           = entry_node->getDoubleValue("life", 900.0);
 
      sm->trigger->setBoolValue(false);
      sm->timer = sm->delay;

src/Systems/submodel.hxx

@@ -41,6 +41,7 @@ public:
   double             yaw_offset;
   double             pitch_offset;
   double             drag_area; 
+  double             life;
  } submodel; 
 
  typedef struct {