How To Add Control Algorithms

1. Overview

• In the How To Make New Components tutorial, we have newly made components emulating codes and adding the new components into our simulation scenario.
• Now we can simulate the behavior of spacecraft free motion and emulate the behavior of sensors and actuators.
• This tutorial explains how to add a Control Algorithm to the simulation scenario.
• For a practical satellite project, we should implement the control algorithm as actual flight software like C2A into the S2E. However, using actual flight software is usually overdoing for use cases such as research and the initial phase of satellite projects.
• So, we introduce the following three methods, and users can choose a suitable method.
  • Direct method: Directly control physical quantity without sensors, actuators, and their noises
    • For theoretical research and preliminary analysis for satellite projects
  • Component method: Control using sensors and actuators without flight S/W framework
    • We can include sensing and actuation noise.
    • For engineering research and preliminary analysis for satellite projects
    • From v6.0.0, we have ideal and real directories in the s2e-core/src/components. Users can use ideal components for the early stage of the analysis and can use real components for more detailed analysis. Mixing these components is also possible.
  • Flight S/W method: Control using sensors and actuators with flight S/W framework
    • For actual satellite projects
• The supported version of this document
  • Please confirm that the version of the documents and s2e-core are compatible.

2. Direct method

• This chapter introduces how to add a control algorithm without sensors and actuators.
• This method directly measures the satellite's physical quantity and generates torque and force acting on the satellite.
• To do that, users need to edit the Update function in the UserSat.cpp.
  • A sample code is in s2e-user-example/sample/how-to-add-control-algorithm-direct-method
• The UserSatellite class already has satellite attitude, orbit, and local environment information since it inherits the Spacecraft base class. So users can easily access these values.
• To measure physical quantities, users can use getter functions defined in the Attitude, Orbit, and LocalEnvironment classes as dynamics_->GetAttitude().GetAngularVelocity_b_rad_s().
• To generate torque and force, users can use dynamics_->AddTorque_b_Nm and dynamics_->AddForce_b_N.
• The sample codes are in SampleCodes/control_algorithm/direct_method/user_satellite.cpp, and you can see very simple detumbling with the proportional control method.
• By using the sample code with initial angular velocity = [0.05, -0.03, 0.01] rad/s, the following results are given.

  • You need to edit the initialize file to set the initial angular velocity.

    

3. Component method: Using ideal components

• TBW
• Users can refer the s2e-ff as an example of the ideal component method.

4. Component method: Using real components

• This chapter introduces a method to add a control algorithm using realistic sensors and actuators. - This method measures a satellite's physical quantity via sensors, generates torque and force via actuators, and executes control algorithms on OBC.
• This tutorial assumes the spacecraft has a three-axis gyro sensor, a reaction wheel, and an OBC.
• The sample codes are in s2e-user-example/sample/how-to-add-control-algorithm-using-real-component.
• Firstly, users need to make the UserOnBoardComputer class to emulate the OBC.
  • Copy the user_on_board_computer files to the s2e-user/src/components from the component_method/src/components, and add the user_on_board_computer.cpp to the set(SOURCE_FILES) in the CMakeLists.txt to compile it.
  • The UserOnBoardComputer class has the UserComponents class as a member, and users can access all components to get sensing information or set the output of actuators.
  • In this tutorial, the angular velocity is measured by the gyro sensor. After that RW's output torque is calculated using the X-axis of the measured angular velocity, and the torque is set to RW.
• Next, users need to add the UserOnBoardComputer into the UserComponents class. You can copy the user_components files to the s2e-user/src/simulation/spacecraft from the component_method/src/simulation.
• Finally, users need to add new source codes to the CMakeLists.txt to compile them.
  • You have to add reaction_wheel_xxx.ini to s2e-user/data/initialize_files/components
  • Refer to SampleCodes/control_algorithm/component_method/data/reaction_wheel_xxx.ini if necessary.
• By using the sample code, the following results are given.

  • The X-axis angular velocity is controlled, but other axes are not controlled well since the satellite only has an RW on X-axis. The X-axis angular velocity has offset value since the gyro has offset noise.

    

  • The following two figure shows the observed angular velocity by gyro and the rotation speed of the RW. You can find the observed X-axis angular velocity reaches zero by the control.

    

5. FlightSW method: Control algorithm within C2A

• TBW
• Users can refer the s2e-aobc as an example of the flight software method.