5.3. Propagator Settings: Termination Settings

The propagation TerminationSettings are a key parameter in the propagation of a body’s orbit, since these will determine the computational time and the size of the output file. Depending on the application, the user may want to end the body propagation according to different criteria. Currently, the following TerminationSettings are offered in Tudat:

  • Termination once a certain time has passed.
  • Termination once a dependent variable meets a certain criterion.
  • Termination once multiple criteria are met.

The different types of TerminationSettings are implemented by means of derived classes and custom constructors, as detailed in this page.

class PropagationTimeTerminationSettings

As the name suggests, these settings will cause the propagation to terminate after a certain time has passed. Please note that the simulator will finish the final time-step, which may cause the termination time to be slightly overpassed. The PropagationTimeTerminationSettings are passed as shown:

boost::shared_ptr< PropagationTerminationSettings > terminationSettings =
      boost::make_shared< PropagationTimeTerminationSettings >( terminationTime );

where:

  • terminationSettings

    boost::shared_ptr that is passed to one of the derived classes of PropagationSettings discussed in Propagator Settings: Basics.

  • PropagationTimeTerminationSettings

    Indicates to boost::make_shared the constructor of the derived class being used.

  • terminationTime

    double that dictates the time that must pass before the simulation is terminated.

class PropagationDependentVariableTerminationSettings

A more powerful method is the use of a DependentVariable to terminate a propagation. Using this class will terminate the propagation once the chosen dependent variable meets a certain criterion. To do so, the user needs to first create the dependent variable that will dictate the termination of the propagation:

boost::shared_ptr< SingleDependentVariableSaveSettings > terminationDependentVariable =
      boost::make_shared< SingleDependentVariableSaveSettings >(
          altitude_dependent_variable, "Vehicle", "Earth" );

where in this example the variable created is an altitude_dependent_variable which provides the altitude of Vehicle with respect to Earth.

The versatility in the use of PropagationDependentVariableTerminationSettings to terminate a simulation lies in the large number of dependent variable types available in Tudat. The user is referred to Propagator Settings: Dependent Variables for a full list of the available dependent variables as well as their use.

Once the dependent variable that terminates the simulation has been created, it must be passed to the terminationSettings:

boost::shared_ptr< PropagationTerminationSettings > terminationSettings =
     boost::make_shared< PropagationDependentVariableTerminationSettings >(
         terminationDependentVariable, limitValue, useAsLowerLimit );

where:

  • PropagationDependentVariableTerminationSettings

    Indicates to boost::make_shared the constructor of the derived class being used.

  • terminationDependentVariable

    Contains the dependent variable used for termination, in this example altitude_dependent_variable as declared above.

  • limitValue

    double that provides the lower-limit (or higher-limit) that the :literal:`` can take before terminating the propagation.

  • useAsLowerLimit

    bool that dictates whether the limitValue is used as a lower-limit (true) or as a higher-limit (false).

class PropagationHybridTerminationSettings

It may be possible that the user desires to terminate a propagation according several criteria, where such criteria may or may not be fulfilled simulataneously. To do so, the user must include the following code:

boost::shared_ptr< PropagationTerminationSettings > terminationSettings =
      boost::make_shared< PropagationHybridTerminationSettings >(
          terminationSettingsList, fulFillSingleCondition );

where:

  • PropagationHybridTerminationSettings

    Indicates to boost::make_shared the constructor of the derived class being used.

  • terminationSettingsList

    std::vector< boost::shared_ptr< PropagationTerminationSettings > > where each of its elements contains derived classes of TerminationSettings. The desired TerminationSettings can be added by using the push_back method of std::vector, where the pushed elements are the terminationSettings objects discussed above for PropagationTimeTerminationSettings and PropagationDependentVariableTerminationSettings.

  • fulFillSingleCondition

    bool that determines whether the propagation terminates once a single condition is met (true) or whether all conditions must be met (false).