Feature/625 mujoco [draft]

[juan-g-bonilla]

• Tickets addressed: Closes MuJoCo as simulation module #625
• Review: By commit
• Merge strategy: Merge (no squash)

Description

This PR adds a new paradigm for dynamics simulation. It makes use of the MuJoCo library for multi-body dynamics. A new DynamicObject is added, MJScene, whose purpose is to expose an interface that can interoperate with the rest of the Basilisk framework, while internally using MuJoCo to solve the complicated dynamics of a multi-body system. Scenarios have been added that showcase the current capabilities.

This feature should be considered in "alpha". Any and all code is subject to considerable refactors in the near future. Validation efforts are not complete; do not use this feature to produce results that you actually care about.

Verification

Tests have been added in src/simulation/dynamics/mujoco/_UnitTest and scenarios in examples/mujoco (src/tests/test_scenarioMujoco.py checks that these scenarios run).

Documentation

The scenarios documentation page has been updated to include a new section Multi-Body Dynamics Simulations with MuJoCo.

Future work

Things still to figure out (non-exhaustive):

• Stateful SysModel (for models that define states with derivatives to be integrated by MJScene.
• Possibly rework how the inertial properties (mass, etc.) are updated.
• Allow prescribing joints and mass.
• Add torque to the gravity model NBodyGravity.
• Add hooks for vizard.
• Add more tests to compare results and performance of spacecraft and MJScene