Fix erasure of Integrator subsystems

Author: A-CGray

openconcept/mission/mission_groups.py

@@ -212,10 +212,18 @@ def _setup_procs(self, *args):
         # (This IntegratorGroup is never added directly to the OM model)
         time_units = self._oc_time_units
         num_nodes = self.options["num_nodes"]
-        self.add_subsystem(
-            "ode_integ",
-            Integrator(time_setup="duration", method="simpson", diff_units=time_units, num_nodes=num_nodes),
-        )
+        try:
+            # In OM 3.40 and later, static_mode is no longer True when this method is called, which leads to any
+            # subsystems that are added here to later be erased. So here we force static_mode to True while we add the
+            # Integrator subsystem to get around the issue. See https://github.com/OpenMDAO/OpenMDAO/issues/3621 for
+            # more details
+            self._problem_meta['static_mode'] = True
+            self.add_subsystem(
+                "ode_integ",
+                Integrator(time_setup="duration", method="simpson", diff_units=time_units, num_nodes=num_nodes),
+            )
+        finally:
+            self._problem_meta['static_mode'] = False
 
         # Call om.Group's _setup_procs which does a lot of things as an initial phase of setup.
         # We pass *args because the signature of this method varies depending on the OM version.