.. _scenarioHelioTransSpice:

scenarioHelioTransSpice
=======================

Overview
--------

The purpose of this simulation is to illustrate how to set a spacecraft's heliocentric translational motion using
custom Spice files. This allows the user to easily visualize a mission trajectory using Vizard.

The script is found in the folder ``xmera/examples`` and executed by using::

      python3 scenarioHelioTransSpice.py

Configuring Translational Motion Using Custom Spice Files
---------------------------------------------------------

To set up the spacecraft's heliocentric translational motion via custom Spice files, the user should first create a
string list containing the desired file names to upload. This script loads a single Spice file::

    customSpiceFiles = ["spacecraft_21T01.bsp"]

Next, the ``loadSpiceKernel()`` method of class SpiceInterface should be called to load the custom Spice files.
This method accepts a file name and the path to the desired file to load::

    spiceObject.loadSpiceKernel(file, os.path.join(path, "dataForExamples", "Spice/"))

Note that setting up the orbital elements and initial conditions using the ``orbitalMotion`` module is no longer needed.

After the Spice files are loaded, the final step is to connect the configured Spice translational output message to
the spacecraft object's ``transRefInMsg`` input message::

    scObject.transRefInMsg.subscribeTo(spiceObject.transRefStateOutMsgs[0])

Finally, add the Spice object to the simulation task list::

    scSim.AddModelToTask(simTaskName, spiceObject)

Ensure to unload the Spice kernels at the end of each simulation::

    spiceObject.unloadSpiceKernel(file, os.path.join(path, "dataForExamples", "Spice/"))

Simulation Visualization In Vizard
----------------------------------

The following image illustrates the expected visualization of this simulation script.

.. image:: /_images/static/scenarioHelioTransSpice.jpg
   :align: center