Orbit Generation

Overview

Project imports orbital information and generates rigid body tumble motion using a 4th Order Runge-Kutta Integrator. The code outputs two files, the tumble attitude and the sun vector. Both are expressed in quaternion.

Requirements

Matlab Version	R2023a
Toolbox	Aerospace
	Signal Processing

Operation Procedure

To run the code, open Q_sunV_generator.m and modify the settings section found at line 38.

Uses one function from the MATLAB Aerospace toolbox to convert between reference frames.

Orbit Setting

% Orbital Settings
ID = 33500;                             % [int] TLE object identifier. See ./utils/getSatelliteTLE.m to add different orbits.
dtUTC = datetime('now', 'TimeZone','Z');% dtUTC = datetime(2023, 5, 25, 12, 0, 0, 'TimeZone', 'Z'). The date influences position in orbit and sun vector calculation.

• Select predefined TLE represented orbit by ID
• Or, you can define orbit as TLE getSatelliteTLE.m
• dtUTC is a time setting parameter to decide sun light vector and on-orbit position

Sun Vector Setting

number_orbits = 1;                      % [double]  Number of orbits to simulate
sunV_ECI = approxECISunPosition(dtUTC); % Sun Vector Settings [x,y,z] unit vector. NOTE: KHI project special request sun vector can be found in section "Obtain sun vector" (~line 200)
sunV_ECI = sunV_ECI/norm(sunV_ECI);     % Or enter your own vector. Example: sunV = [1,0,0];

• In the code above, sunV_ECI, which is sun vector in Earth Centered Inertia Frame, is automatically calculated by dtUTC.
• Or, you can set sun vector in ECI directory. They are expressed in [x, y, z] elements.

Tumbling Setting

% Tumble Motion Settings
Q_import = false;                       % [boolean] If importing tumble motion data set to true
% If importing tumble data (Q_import = true)
import_filename = 'gravity_gradient_motion_array.mat'; % File path of the data to be imported
import_time_step = 1;                   % [s] The imported data has a timestep that may be different than our requested timestep
% If generating tumble data (Q_import = false)
q_initial = [1,0,0,0]';                 % Initial attitude quaternion [qw, qx, qy, qz]' 
w_initial = [0,0,0,pi()/180]';          % [0, wx, wy, wz]' [rad/s] initial relative rotation
dt = 0.1;                               % [s] simulation timestep (4th order Runge-Kutta) <--- NOTE: time_step >= dt
sim_plot = true;                        % [boolean] whether to show the energy and angular velocity plots
sim_viewer = false;                     % [boolean] whether to show the orientation viewer (NOTE: the program will not continue while the viewer is running)
I = [27548.8, 0,       0;               % [kgm2] object inertia matrix
     0,       27675.3, 0; 
     0,       0,       6808.8]; 

Time[s]	In Plane Angle[deg]	Out Of Plane Angle[deg]	Pitch[rad]	Roll[rad]	Target Nose Vector in Hill Frame x[m]	y[m]	z[m]
0	45	-45	0.785	0.615	-0.707	0.408	0.577
...	...	...	...	...	...	...	...
1999	-30	-44	-0.529	0.696	0.504	0.553	0.663

• You can chose import motion data or simulate in this code.
• If you set Q_import as true, .mat file will be imported. This is array which looks like above. (not included headers)
• If you set Q_import as false, you need set initial state of target.
• q_initial is initial attitude quaternion. Default is [1, 0, 0, 0] and it is rarely modified.
• w_initial is initial velocity of target. First element should be zero, and others represent rotation around [x, y, z]
• I is initial inertia matrix