Getting Started

1. Overview

This tutorial explains how to use the S2E simulator without any source code modification.
Users can start this tutorial just after users clone the s2e-core repository.
The supported version of this document
- Please confirm that the version of the documents and s2e-core is compatible.

Clone s2e-core.
Read README.md to check the overview of S2E.
Build and execute the s2e-core by referring following documents depends on your development environment.
- How to compile with Visual Studio
- How to compile with Ubuntu

Check ./data/sample/logs to find CSV log output file
- The file name includes executed time as YYMMDD_HHMMSS_default.csv
- The included executed time is defined by the user computer settings.
Open the CSV log file
You can see the simulation output
The meaning of each value is described in the first row
- A general rule of the header descriptions are summarized here.
You can write a graph from the CSV file as you need.
- You can find plot examples written in Python in the scripts/Plot directory.
- Please see How to Visualize Simulation Results for more details.

Move to ./data/sample/initialize_files directory
You can find the several initialize files (INI files). In these initialize files, simulation conditions are defined, and you can change the conditions without rebuild of S2E by editing the initialize files.
Open sample_simulation_base.ini, which is the base file of the initialize files.
- In this base file, other initialize files are defined.
- You can see simulation conditions as time definitions, randomize seed definitions, etc.
Open sample_satellite.ini, which is the file to set the spacecraft parameters.
Edit the value of angular momentum initial_angular_velocity_b_rad_s(0-2) in the [Attitude] section as you want.
Set the value of initialize_mode to MANUAL if it is CONTROLLED.
Rerun the s2e-core without a rebuild
Check the new log file in ./data/sample/logs to confirm the initial angular velocity is changed as you want.
Of course, you can change other values similarly.

Move to ./data/sample/ini directory again
Open sample_disturbance.ini, which defines conditions to calculate orbital disturbance torques and forces
- Currently, S2E supports the following disturbances:
  - Gravity Gradient torque
  - Magnetic Disturbance torque
  - Air drag torque and force
  - Solar radiation pressure torque and force
  - Geo Potential acceleration
  - Third body gravity acceleration
You can select ENABLE or DISABLE of calculation and log output for each disturbance
Edit all calculation parameters of each disturbance as calculation = DISABLE
Rerun the s2e-core without a rebuild
Check the new log file in ./data/sample/logs to confirm the spacecraft is not affected by any disturbance torque and the angular velocity and quaternion are not changed. You can also plot by following command and see all the disturbance torque and force are zero. (assuming you already created a pipenv virtual environment)
```
# Windows
cd scripts/Plot
pipenv run python .\plot_disturbance_torque.py --file-tag <log file tag>
pipenv run python .\plot_disturbance_force.py --file-tag <log file tag>
```
Edit calculation of [THIRD_BODY_GRAVITY] as calculation = ENABLE
Rerun the S2E_CORE without a rebuild
Rerun the python script to check the third body gravity is generated.

Move to ./data/sample/ini directory
Open sample_satellite.ini and see the [Orbit] section, which defines conditions to calculate orbit motion
- Currently, S2E supports several types of orbit propagation. Please see Orbit specification documents for more details.
Please set the parameters as follow:
- propagate_mode = SGP4: SGP4 Propagator
- initialize_mode is not used in the SGP4 propagate mode.
- TLE: ISS orbit (default)
To get a long-term orbit simulation data, edit the following simulation time settings in sample_simulation_base.ini
- simulation_duration_s = 6000
- log_output_period_s = 10 (to decrease the output file size)
To visualize the orbit result, execute the plot_satellite_orbit_on_miller.py and plot_orbit_eci.py by following command. You can see the plots as follows. Please see general documents for more details on visualization of simulation results.
```
# Windows
cd scripts/Plot
pipenv run python .\plot_satellite_orbit_on_miller.py --file-tag <log file tag>
pipenv run python .\plot_orbit_eci.py --file-tag <log file tag>
```

Change TLE as you want

Example: PRISM (Hitomi)

tle1=1 33493U 09002B   22331.71920614  .00003745  00000-0  29350-3 0  9995
tle2=2 33493  98.2516 327.9413 0016885   9.3461 350.8072 15.01563916753462

Rerun the s2e-core without a rebuild
Check the new log file in ./data/sample/logs to confirm the spacecraft position in ECI frame spacecraft_position_i is changed.
To visualize the orbit result, execute the plot_satellite_orbit_on_miller.py and plot_orbit_eci.py. You can see the different plots as follows.

Move to ./data/sample/ini directory
Open sample_local_environment.ini, which defines conditions to calculate the environment around the spacecraft
- Currently, S2E supports the following environment models:
  - Celestial information: CSPICE
  - Geomagnetic field model: IGRF with random variation
  - Solar power model: Considering solar distance and eclipse
  - Air density: NRLMSISE-00 model with random variation
Edit values of magnetic_field_random_walk_standard_deviation_nT, magnetic_field_random_walk_limit_nT, magnetic_field_white_noise_standard_deviation_nT
Rerun the s2e-core without a rebuild
Check the new log file in ./data/sample/logs to confirm the magnetic field at the spacecraft position in ECI frame geomagnetic_field_at_spacecraft_position_i, the magnetic field in body frame geomagnetic_field_at_spacecraft_position_b, and magnetic disturbance torque in body frame magnetic_disturbance_torque_b are changed.