SPEL - Open Star Tracker (SOST)

1.- Overview

This GitHub offers to the CubeSat research community an open-source Star Tracker (STT), developed at the Space and Planetary Exploration Laboratory (SPEL) at the University of Chile. We will use this development in our following satellites.
SUCHAI-1 was the first NanoSatellite developed by the University of Chile at SPEL. Launched on June 23 (2017), this satellite worked 457 days on space. Today in SPEL, we are working on three new NanoSatellites, the SUCHAI 2 & 3 and PlantSat. These new satellites will have pointing capabilities, with a robust attitude determination and control system (ADCS).
---> Links of interest:

• SUCHAI-1
  
• The SUCHAI project
  
• PlantSat project
  
• SPEL
  
• SOST paper in IEEE ACCESS
  

2.- Description

• This GitHub contains a fully functional Star Tracker that you can test on a Linux PC. Nevertheless, the main idea is to use it with a Raspberry Pi (RPi) and its camera (V2.1) in an autonomously way.
• This code is written in Python 2.7. All the code and the necessary files are in the RPI folder.
• This GitHub is free and open to everyone interested in using it, especially researchers working on CubeSats. We encourage interested researchers to aid in growing up this project!

3.- Installation instructions

1. Two open software commonly used in the astronomy field: Source Extractor and Match, are the base of this STT code. To use this STT, you need to install first these two software. You can do it manually in the following way:
   1.1.- Get and install Source Extractor. You can find this program in the Linux (RPI) repository, and install it by typing in the terminal:

   sudo apt install sextractor

   We use version 2.19.5 in our implementation.
   1.2.- Get and install Match. We use version 0.14 in our program.
   As an alternative to this installation, you also can install these software using the script called stt_installer.sh, which is in the RPI folder. Type the following in the terminal:

cd RPI
./stt_installer.sh

2. This STT software uses the Python-Astropy package. You can install it by typing in the terminal:

pip install astropy

3. Finally, clone this repository in any folder on your RPI. For example, you can type the following in the terminal:

mkdir Git
cd Git
git clone https://github.com/spel-uchile/Star_Tracker.git

4.- Use instructions

This STT software works by comparing the acquired picture with a stellar catalog. The different catalog segments can be separated by 5, 10, or 15 degrees. You can choose it when you run the program. You can test this STT program with RPi pictures or with STEREO HI-1 pictures.

4.1.- To use it with Raspberry Pi pictures

By default, this software will use a picture from /RPI/Sample_images/. You can test it with other pictures on the same folder, or use your pictures taken with a Raspberry Pi V2.1 camera.

1. For a 10 degrees catalog separation, run in the terminal:
   

python StarTracker_10_deg.py

2. For a 5 degrees catalog separation, run in the terminal:
   

python StarTracker_5_deg.py

4.2.- To use it with STEREO pictures

This STT software can also be tested with pictures from the HI-1 detector from the STEREO mission. This procedure proves that different cameras can be used with this algorithm, and it is not attached to particular hardware.
The STEREO HI-1 pictures can have different processing levels. These levels are well explained in STEREO HI data processing documentation. We use two different image format:

• L0 images, which can be download from STEREO SCIENCE CENTER - L0.
• L2 images, which can be download from STEREO SCIENCE CENTER - L2.

There are examples of pictures of both kinds in folder /RPI/STEREO_pics/.

1. For a 10 degrees catalog separation, run in the terminal:

python StarTracker_10_deg_FITS.py <full_path_to_HI-1_picture>

2. For a 5 degrees catalog separation, run in the terminal:

python StarTracker_5_deg_FITS.py <full_path_to_HI-1_picture>

The attitude information can be read from the STEREO image header. Various software can be used for it, for example, DS9.

5.- Research

This STT is deeply tested with theoretical analysis and ground-based night-sky pictures. The tools, algorithms, methods, and results are fully described in my paper in IEEE ACCESS.

If you are using this open project in your research or development, please cite it using the following BibTeX:

@article{gutierrez2020introducing,
  title     = {Introducing SOST: An Ultra-Low-Cost Star Tracker Concept Based on a Raspberry Pi and Open-Source Astronomy Software},
  author    = {Guti{\'e}rrez, Samuel T and Fuentes, C{\'e}sar I and D{\'\i}az, Marcos A},
  journal   = {IEEE Access},
  volume    = {8},
  pages     = {166320--166334},
  year      = {2020},
  publisher = {IEEE}
}

6.- Any questions?

Contact: Samuel T. Gutiérrez.
Ph.D.(c) in Electrical Engineering at the University of Chile, Santiago, Chile.
e-mail: samuel.gutierrez@ug.uchile.cl

README updated June 28, 2021, by SGR.