Spec_Attitude.md

Specification for Attitude

1. Overview

1. functions

• The Attitude class calculates the attitude and angular velocity of a satellite with the following propagation modes.
  • RK4 : 4th order Runge-Kutta propagation with disturbances and actuators output torque. Users use this mode to consider attitude control algorithm.
  • CONTROLLED : Satellite attitude is perfectly controlled to the setting direction. This mode doesn't consider the disturbances and actuators output torque. Users use this mode when they focus on orbit dynamics or mission analysis.

2. files

• src/dynamics/attitude/attitude.hpp, .cpp
  • Definition of Attitude base class
• src/dynamics/attitude/initialize_attitude.hpp, .cpp
  • Make an instance of Attitude class.

3. How to use

• Make an instance of the attitude class in Initialize function in dynamics.cpp
  • Usually, users don't care this process.
• Select propagate_mode in the spacecraft's ini file.
  • RK4 or CONTROLLED described above.
• Select initialize_mode in the spacecraft's ini file.
  • When users select propagate_mode = CONTROLLED, initialize_mode is not used, and the attitude is initialized with [CONTROLLED_ATTITUDE] settings.
  • When users select propagate_mode = RK4, initialize_mode is used.
    • initialize_mode = MANUAL
      • Initial attitude is defined by initial_quaternion_i2b and initial_angular_velocity_b_rad_s.
    • initialize_mode = CONTROLLED
      • Initial attitude is defined by [CONTROLLED_ATTITUDE] settings. By using this mode, users can easily choose the required initial quaternion without complicated calculation.

2. Explanation of Algorithm

In the Attitude base class provides the following common functions for every propagator.

• Getter functions

  • The base class has several getter functions for the member variables.

• CalcAngularMomentum

  • This function calculates angular momentum of spacecraft including internal actuators such as reaction wheels.

3. Results of verifications

• The verification results are described in the document of each propagation method.

4. References

NA