Sun sensors are a sub-system aimed at determining the position of the sun relative spacecraft. OSIRIS, the sun sensor project, is an effort to design and manufacture hardware and software for a Coarse Sun Sensor (CSS). The latest phase, OSIRISv2, is the first working prototype and has been developed to help estimate the direction of the sun.

Learning Through Real-World Sensor Challenges

While initial designs assumed idealised sensor behaviour, OSIRISv2 addresses the practical realities of photodiode responses that don’t perfectly follow ideal Lambertian responses. The team discovered that the VEMD5510FX01 photodiodes used in the sensor exhibit angular sensitivities that differ from the expected cosine falloff.

To work with this, we have developed an algorithm, a polynomial correction method designed to better translate the sensor readings into approximate sun angles. This approach helps improve the accuracy of sun vector estimation within the limits of their low-cost, student-built hardware.

Practical Experience and Educational Value

• Hands-on Hardware Development: Understanding operational amplifiers and integrating ADCs to interface with Arduino and ESP32 microcontrollers.

• Algorithmic Exploration: Developing correction techniques to account for real sensor characteristics.

• 3D Vector Estimation: Applying linear algebra to calculate sun direction from sensor data.

Next Steps Toward OSIRISv3

With OSIRISv2 testing quickly approaching, the team plans to rigorously test the prototype to determine its accuracy and identify areas of improvement. The team plans to later develop OSIRISv3, which will be built specifically for the second High Altitude Balloon mission, integrating with FISH and potentially the ADCS integration board.