Server side of GranaSAT experiment, selected for BEXUS 19 campaign.
The client side code can be seen in its GitHub page.
The final Student Experiment Documentation (SED), which includes all the technical details, the software architecture and the results, can be found in the REXUS/BEXUS page.
GranaSAT designed and built a low-cost attitude determination system, a fundamental system for any spacecraft, based in a star sensor, horizon sensor and the magnetic field and acceleration measurements. The same Charge Coupled Device was used for both the star sensor and the horizon sensor. For the star sensor the Lost in Space functionality was designed, the identification algorithm used is a variation of the Matching Group algorithm proposed by Van Benzooijen; for the horizon sensor a simple detection algorithm is proposed, with the circle fitting method based in Umbach and Jones work and for the magnetometer and accelerometer sensors the attitude was estimated by two vector matching procedure based in Wahba solution.
The star sensor was capable to obtain an attitude matrix for the 97.80 % of the images collected. The relative error in the angles measured was kept below 1% through a camera calibration and the error obtained in the attitude matrix obtained was found less than 250 arcsecs. The horizon sensor was able to process all the images in night conditions, but it did not fulfil the 5o accuracy requirement. Finally, for the magnetometer and accelerometer sensors, an in-flight calibration was used to keep an uncertainty of the attitude angles under 4o with a maximum standard deviation in the magnetometer measurements of 140 nT.
After the results obtained, the most accurate and preferable method is the star sensor, despite its complexity. If low accurate attitude estimation or less complex solutions are required, the horizon sensor or magnetometer and accelerometer sensor solutions are valid for a spacecraft attitude determination system.
The software architecture is briefly summarized in the following diagram; for technical details and a comprehensive explanation of the code, please read the SED carefully.
The experiment flew, successfully, the night of 8 October 2014. Thousands of good images were collected, both for the Horizon Sensor and for the Star Tracker. The scientific and technical results were exposed at the 22nd ESA Symposium on European Rocket and Balloon Programme & related Research, 7-12 June 2015.
While you read the technical details in the paper and the SED, you can enjoy the beautiful aurora borealis captured by our camera from the stratosphere :)
See more information at GranaSAT website.
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Alejandro García (@agarciamontoro), Manuel Milla and Mario Román (@m42)
========================== The REXUS/BEXUS programme is realised under a bilateral Agency Agreement between the German Aerospace Center (DLR) and the Swedish National Space Board (SNSB). The Swedish share of the payload has been made available to students from other European countries through a collaboration with the European Space Agency (ESA).