Printing and processing the results
The results of the numerical propagation are stored in the propagation results, which can be used to perform further
analysis, and retrieve the details of the propagation process. In addition, there are a number of processing steps and terminal outputs that
Tudat can perform before, during and after the propagation. Although such settings can be provided directly
when creating propagator settings (for instance, when calling the
function), it is adviced to modify these settings afterwards:
propagator_settings = propagator.translational( ... ) console_print_settings = propagator_settings.print_settings post_processing_settings = propagator_settings.processing_settings
Here, the resulting settings object for console printing and post-processing are of type
(with derived class
for single-arc propagation), respectively. Below, the options available in both these settings objects are described in more
By default, Tudat will save the propagated states and dependent variables at each time step, and return these the user after the propagation is finished. Below, a number of additions/extensions to this behaviour are described, where the propagated states that are returned are used and/or processed before being returned to the user.
Updating ephemerides (and other environment models)
Tudat can be set up to automatically use
the results of the numerical propagation to reset properties in the environment upon the successful completion of the propagation.
This option can be toggled using the boolean attribute
propagator_settings = propagator.translational( ... ) propagator_settings.processing_settings.set_integrated_result = True
Specifically, this will result in:
Translational dynamics: use the numerical results to reset the ephemeris of the body with (using the default) a 6-th order Lagrange interpolation scheme to create a tabulated ephemeris
Rotational dynamics: use the numerical results to reset the rotational ephemeris of the body with (using the default) a 6-th order Lagrange interpolation scheme to create a tabulated rotation model
Mass dynamics: use the numerical results to reset the mass function of the body with (using the default) a 6-th order Lagrange interpolation scheme
Multi-type dynamics: automatically processes all of the constituent dynamics as listed above
Custom dynamics: no action
To be able to perform the reset of the ephemeris (or other environment model), the existing ephemeris must be of the suitable type. This means that it must either be a tabulated ephemeris already (in which case the tabulation is reset) or the body must contain no ephemeris (in which case one is created on the fly when creating the dynamics simulator.
In cases where a user wants to use a
non-tabulated ephemeris for a body, but still use the functionality described here to reset the ephemeris later on, the ephemeris type of the
body can be redefined using
when defining the body settings. In essence, this converts any ephemeris into a tabulated ephemeris,
where the tabulated ephemeris is populated by states from the original (non-tabulated) ephemeris.
For specific applications, most notably a state estimation, a user may want the numerical solution to only be used to reset the environment,
while not needing access to the numerical results directly.
To enable this behavior, the boolean attribute
PropagatorProcessingSettings class is provided.
propagator_settings = propagator.translational( ... ) propagator_settings.processing_settings.set_integrated_result = True propagator_settings.processing_settings.clear_solution = True
When set to true, the numerical results of the propagation are completely deleted after the propagation is performed. When this option is selected, the numerical results ‘live on’ only in the environment models that have been reset, but are no longer available from the propagation results. This option may be attractive when memory usage of the application is a concern.
Reduced saving cadence
By definition, Tudat saves and returns the state and dependent variables at every full step of the numerical integration.
For long numerical integrations, this can result in excessively long data structures being stored in memory, potentially
leading to issues. Options are provided to modify the cadence at which data is saved, using the
results_save_frequency_in_seconds attributes of
which allow the results to be saved only every X steps, or every Y seconds (of time in the simulation). For instance, using:
propagator_settings = propagator.translational( ... ) propagator_settings.processing_settings.results_save_frequency_in_steps = 3
The results are only saved every third time step. By using
propagator_settings = propagator.translational( ... ) propagator_settings.processing_settings.results_save_frequency_in_steps = 3 propagator_settings.processing_settings.results_save_frequency_in_seconds = 60.0
the results are saved every third time step or every 60 seconds of time in the simulation, whichever one occurs first since the previous saved data point.
Multi- and hybrid-arc considerations
For the multi- and hybrid arc propagation, the setting of the numerical results in the environment,
and the clearing of the numerical solution (as described above, is always consistent between all the arcs.
As a result, these settings in the constituent single-arc propagation settings will be overridden
by the settings in the multi- or hybrid-arc propagation settings. Objects of type
HybridArcPropagatorProcessingSettings are automatically
created and stored in the propagator settings when creating multi- or hybrid-arc propagator settings, and can be retrieved similarly as for the single-arc settings:
multiarc_propagator_settings = propagator.multi_arc( ... ) post_processing_settings = propagator_settings.processing_settings
To reset the dynamics of a body with the results of a multi-arc propagation (e.g. if the
set_integrated_result option is set to true),
the ephemeris of this body must be a multi-arc ephemeris. If the body has no ephemeris before propagation,
one is created on the fly when creating the dynamics simulator.
In cases where a user wants to use a
single-arc ephemeris for a body, but still use the functionality described here to reset the ephemeris from multi-arc results later on,
the ephemeris type can be forced to multi-arc by using the
make_multi_arc_ephemeris attribute of the
EphemerisSettings when defining the body settings.
For example, to reset the ephemeris of the Earth from a multi-arc propagation result, the following can be used to permit this:
# Create body settings body_settings = environment_setup.get_default_body_settings( ... ) body_settings.get("Earth").ephemeris_settings.make_multi_arc_ephemeris = True
The cadence at which data is saved during the propagation (see above) may vary per arc. The list of single-arc settings can be retrieved from the results as follows:
multiarc_propagator_settings = propagator.multi_arc( ... ) single_arc_processing_settings = multiarc_propagator_settings.single_arc_settings
Settings to print data to the console (see below) is also defined seperately per arc. Additional options for multi- and hybrid-arc propagation are provided below
Tudat also provides a range of options on information to be printed to the console during the process of the propagation.
These settings are specified through a
which can be retried from single-arc propagator settings through:
propagator_settings = propagator.translational( ... ) console_print_settings = propagator_settings.print_settings
A full list of print options is provide in the API documentation. Typical examples of information that can be printed to the console are:
The indices in the full dependent variable vector (
print_dependent_variable_indices; see Dependent Variables) where each separate dependent variable is stored, with a brief text description of the associated dependent variable (printed before the propagation starts)
The current time and state can be printed during the propagation (
state_print_interval), at a simulation time interval specified by the user
Total runtime, number of function evaluations of the state derivative, and the reason for the termination of the propagation (printed after the propagation is finished; see
In most cases, the separate print settings (as attributes of the
are defined by a boolean (print this information: yes or no).
For specific cases, such as the interval at which information should be printed to the console during a propagation,
are to be provided as a floating point value. To enable all console printing that can be defined by a boolean, the
enable_all_printing() function can be used.
To disable all console printing, us the
An example of defining console output is:
propagator_settings = propagator.translational( ... ) console_print_settings = propagator_settings.print_settings console_print_settings.print_state_indices = True console_print_settings.print_dependent_variable_indices = True console_print_settings.print_propagation_clock_time = True console_print_settings.print_termination_reason = True console_print_settings.print_number_of_function_evaluations = True
which will result in the following terminal output (for a specific script propagating dynamics of Delfi C-3 w.r.t. Earth):
=============== STARTING SINGLE-ARC PROPAGATION =============== PROCESSED STATE VECTOR CONTENTS: [Vector entries], content description [0:5], Translational state of body Delfi-C3 w.r.t. Earth DEPENDENT VARIABLE VECTOR CONTENTS: [Vector entries], content description [0:2], Total acceleration in inertial frame of Delfi-C3 [3:8], Kepler elements of Delfi-C3 w.r.t. Earth PROPAGATION FINISHED. Total Number of Function Evaluations: 43201 Total propagation clock time: 2.94223 seconds Termination reason: Propagation successful; termination condition exceeded =================================================================
Multi- and hybrid-arc console output
For the multi- and hybrid arc simulations, the console output is specified in its constituent single-arc propagation settings where,
in principle, these settings can be different for each arc, and are processed independently.
However, a number of additional options are available for printing output to the console for multi- and hybrid-arc propagation,
For the multi- and hybrid arc propagation, there is an option to ensure identical print settings for each arc (see
For the multi-arc propagation, there is an option to automatically suppress all output for all arcs except the first arc (see
print_first_arc_only) This is typically used in cases where the settings for each arc are largely identical
For the hybrid-arc propagation, the constituent single- and multi-arc settings can be independently modified. These settings can be extracted from the