.. _scenarioAttitudeGG:

scenarioAttitudeGG
==================

Overview
--------

Illustrates how to add a :ref:`GravityGradientEffector` to a 6U cube-sat spacecraft while a Hill-frame pointing
control solution is active.  This script expands on :ref:`scenarioAttitudeGuidance` sets
up a 6-DOF spacecraft which is orbiting the Earth.  More illustrations on using the gravity gradient
torque effector can be found in the modules :ref:`UnitTestGravityGradientEffector` folder.

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

    python3 scenarioAttitudeGG.py

The simulation layout is shown in the following illustration.  The :ref:`GravityGradientEffector` is added
to the spacecraft to create a position depended external torque.  This

.. image:: /_images/static/test_scenarioAttitudeGG.svg
   :align: center

Illustration of Simulation Results
----------------------------------
In this simulation the reference frame is not aligned with the Hill frame, but rather it has a fixed angular
offset along the 2nd body axis.  As the Body frame inertia tensor is diagonal, this reference orientation
represents a non-equilibrium gravity gradient torque orientation.  Thie simulation results are shown in the
following figures:

.. image:: /_images/Scenarios/scenarioAttitudeGG1.svg
   :align: center

.. image:: /_images/Scenarios/scenarioAttitudeGG2.svg
   :align: center

.. image:: /_images/Scenarios/scenarioAttitudeGG3.svg
   :align: center

Where in :ref:`scenarioAttitudeGuidance` the attitude error asymptotically converged to zero, with the
gravity gradient torque the closed loop dynamics is now only Lagrange stable or bounded.