.. _scenarioAttitudePointingPy:

scenarioAttitudePointingPy
==========================

Overview
--------

This script showcases how to create a Python Xmera module.

Demonstrates how to stabilize the attitude tumble without translational motion.
This script sets up a 6-DOF spacecraft, but without specifying any orbital motion.  Thus,
this scenario simulates the spacecraft translating in deep space.  The scenario is a
version of :ref:`scenarioAttitudePointing` where the :ref:`mrpPD` feedback control
module is replaced with an equivalent python based BSK MRP PD control module.

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

    python3 scenarioAttitudePointingPy.py

As with :ref:`scenarioAttitudePointing`, when
the simulation completes 3 plots are shown for the MRP attitude history, the rate
tracking errors, as well as the control torque vector.

The MRP PD control module in this script is a class called ``PythonMRPPD``.  Note that it has the
same setup and update routines as are found with a C/C++ Xmera module.
These Python modules behave exactly as other C++/C modules: they respect their
given priority and can run before C++/C modules.

Similarly to C++ modules, creating an instance of the Python module is done with the code::

    pyMRPPD = PythonMRPPD()
    pyMRPPD.modelTag = "pyMRP_PD"
    pyMRPPD.K = 3.5
    pyMRPPD.P = 30.0
    scSim.AddModelToTask(simTaskName, pyMRPPD)

Illustration of Simulation Results
----------------------------------

::

    show_plots = True

Here a small initial tumble is simulated.  The
resulting attitude and control torque histories are shown below.  The spacecraft quickly
regains a stable orientation without tumbling past 180 degrees.

.. image:: /_images/Scenarios/scenarioAttitudePointingPy1.svg
   :align: center

.. image:: /_images/Scenarios/scenarioAttitudePointingPy2.svg
   :align: center