Simulation

This guide outlines the steps to run Software-In-The-Loop (SITL) simulation with ATMOS and PX4 Autopilot.

Running the Simulator

Before starting, ensure PX4 Autopilot is set up on your local machine as outlined in PX4 Autopilot section. It is also useful to have QGroundControl, outlined in Setting up QGroundControl.

The FreeFlyers with PX4 controller can be simulated using Gazebo. Gazebo should have been installed when setting up required packages for PX4-Autopilot. If not, installation instructions for Gazebo can be found here.

With Gazebo installed, navigate to your local PX4 Autopilot directory and run the simulation:

make px4_sitl_spacecraft gz_atmos

Optionally, to run with ROS 2 namespace:

PX4_UXRCE_DDS_NS=<namespace> make px4_sitl_spacecraft gz_atmos

Running Micro-XRCE-DDS-Agent Locally

PX4 uses Micro-XRCE-DDS as middleware to allow its uORB messages to be published and subscribed to on a companion computer as though they were ROS 2 topics. Although the Micro-XRCE-DDS-Agent is preconfigured on the Jetson, we recommend installing it locally as well for simulation, testing, and development.

Install Micro-XRCE-DDS-Agent from snap-store:

sudo snap install micro-xrce-dds-agent --edge

Once installed, connect to the PX4 by running:

• For Ethernet and Simulator connections:

  micro-xrce-dds-agent udp4 -p 8888
  

• For Serial connections:

  micro-xrce-dds-agent serial --dev <serial-port>
  

Subscribe to topics

Similarly to the hardware version, you should now see the SITL topics being published in ROS 2:

ros2 topic list
ros2 topic echo /fmu/out/vehicle_attitude

Make sure you have sourced the PX4-msgs before publishing and subscribing.

The hardware is now being mimicked in software!

Try Control

In the PX4-MPC repository, we made available a few nonlinear model predictive controller examples for the spacecraft model. We encourage you to follow the steps there provided and try controlling ATMOS!