Specification for Orbit

1. Overview

1. functions

  • The Orbit class calculates the position and velocity of satellites with the following propagation mode.
    • KEPLER : Kepler orbit propagation without disturbances and thruster maneuver
    • SGP4 : SGP4 propagation using TLE without thruster maneuver
    • RK4 : RK4 propagation with disturbances and thruster maneuver
    • ENCKE : Encke's orbit propagation with disturbances and thruster maneuver
    • RELATIVE : Relative dynamics (for formation flying simulation)
  • The KEPLER mode is the simplest and general for all users.
  • The SGP4 mode is useful for LEO satellites users without orbit control.
  • When users need to analyze the orbit disturbance force effect or the orbit control algorithm, the users should choose RK4 or ENCKE mode.
  • For multiple satellite operation, RELATIVE mode is useful.`

2. files

  • src/dynamics/orbit/orbit.hpp, cpp
    • Definition of Orbit base class
  • src/dynamics/orbit/initialize_orbit.hpp, .cpp
    • Make an instance of orbit class.

3. How to use

  • Make an instance of the orbit class in Initialize function in dynamics.cpp
  • Select propagate_mode in the spacecraft's ini file(eg. sample_spacecraft.ini).
  • Select initialize_mode in the spacecraft's ini file(eg. sample_spacecraft.ini).
    • This setting works only for RK4, KEPLER, and ENCKE mode.
  • Set the orbit information in the ini file
    • You can see the details in the documents for each orbit propagation mode.
  • The definition of the coordinate system is decided at [CELESTIAL_INFORMATION] section in sample_simulation_base.ini.

2. Explanation of Algorithm

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

1. UpdateByAttitude function

  • The UpdateByAttitude function simply converts the velocity vector of the spacecraft (in ECI coordinate system) to body coordinate system notation using the argument: quaternion_i2b.

2. SetAcceleration_i_m_s2, AddAcceleration_i_m_s2, AddForce_i_N, AddForce_b_N function

  • These functions provides the interface to include orbital disturbance or control forces.

2. TransformEcefToGeodetic function

  • The TransformEcefToGeodetic function calculates latitude[rad], longitude[rad], and altitude[m]. Currently, we use the Geodetic class to calculate the information.

3. TransformEciToEcef function

  • The TransformEciToEcef function can convert the position and the velocity of the satellite from the ECI frame to the ECEF frame, which considers the earth's rotation.

3. Results of verifications

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

4. References

NA