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Títol: Design and test of a raspberry-based star tracker

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Departament: FIS

Títol: Design and test of a raspberry-based star tracker

Data inici oferta: 12-02-2023     Data finalització oferta: 12-10-2023

Estudis d'assignació del projecte:
Tipus: Individual
Lloc de realització: EETAC
Paraules clau:
Astronomy, Optics, Star tracker, Raspberry, Astrophotography, Astrometry, Image Processing
Descripció del contingut i pla d'activitats:
This project aims to the design, development and test of a small
star tracker using a raspberry, a CMOS camera and an optical

Experimental characterization of the performance of the optical
system and of the CMOS camera (dark current, bias, readout noise)
will be made in a suitable laboratory.

The expected outcomes of the project are the software required to
read the image and determine the centroids of stars, and the use
of a stellar catalog to identify the field, find its centroid and
determine its orientation.
Overview (resum en anglès):
In astronomy and the aerospace world, determining the orientation or attitude of a system in space is of great importance, whether it's simply to determine observations or to successfully carry out space missions.

One of the devices commonly used is the star tracker. These devices allow the determination of attitude based on observed stars, using a preloaded catalogue in the system that identifies which stars are captured. In this work, the catalogue preloaded in the star tracker has been specifically designed for the proposed requirements, a catalogue derived from the Hipparcos catalogue.

The starting point of the design is a Lost In Space (LIS) situation, where the only reference available are the stars that this device can capture and identify correctly.

Traditionally, they have been systems with limited accessibility, only for large organizations or major space projects, due to their high cost and complexity. With the rapid development and advancement of technologies in recent years, today, we can find high-performance technological elements at a reduced cost. In this case, a functional star tracker has been developed and implemented using a Raspberry Pi with the Raspberry Pi OS operating system, a camera, and an optical system. This setup allows capturing images of the celestial sphere.

To capture the images, the MATLAB® package "MATLAB Support Package for Raspberry Pi Hardware" has been used, a package that allows direct connection between the Raspberry Pi operating system and MATLAB®, through a WiFi network or an ethernet cable.

To determine the attitude, it's necessary to find the match between the stars of the preloaded catalogue and the captured stars. In this case, the three brightest stars captured after processing, correcting, and characterizing the image.

To correct the light frame and eliminate random noise and outliers, the master frames of the dark, bias, and flat images have been obtained. Additionally, an average filter has been used to soften and blur the captured stars. To characterize the image, the optimal ISO value, exposure time, aperture, and focus were determined.

Finally, with the corrected image, the centroid of the three brightest stars, and the match found in the catalogue, the rotation matrix was determined using the Kabsch algorithm, a matrix that has allowed determining the attitude of the star tracker.

The attitude has been determined in two ways, with the quaternion and with the Euler angles, with a precision between 1 and 3 arc minutes and a 97,50% satisfactory detection rate.

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