Gravity disturbances

[Moanalengkeek]

Description

Summary of changes

• Created a calculate_grav_torque function which calculates the torque due to gravity on a spacecraft. The model used can be found in chapter 3.3 of https://doi.org/10.1016/j.asr.2018.06.025. This includes up to and including J2 effects.
• Implemented this function in the function calculate_disturbance_torques in attitude_model.py
• Creation of pytests for this additional code

Resolved Issues

• fixes Gravity disturbances in attitude model #196

How Has This Been Tested?

Two tests have been created:

• The first checks whether a 3-axis symmetric, uniform body has no angular acceleration or velocity due to the gravity torque.
• The second checks whether a spacecraft in the shape of a pole (long rectangular prism) has the correct angular accelerations due to gravitational forces.

Related Pull Requests

• Uses the attitude model code of Attitude model v2 #198

This branch was created from the attitude-model branch on 22/01/24. Ideally this branch would have been created when #198 was completed and merged, as it now contains a mostly functional, but still incomplete, attitude model. Additionally, the only difference with the other ranch are the commits from 22/01/24 onward, to implement the gravitational disturbances. Because of this, this pull request should now be merged with student after the attitude-model branch has, and things may need to be re-checked for functionality.

[GabrieleMeoni]

@Moanalengkeek, please, merge from student, which is now containing the attitude model.