Tetralux-1: Design and System Architecture of a Six-Face Photodiode Sun Sensor for CubeSat ADCS

Tetralux-1 is a 1U CubeSat attitude-determination prototype developed as part of a student-led engineering project, designed to estimate the direction of a light source using six photodiodes mounted across the faces of the CubeSat structure. This paper presents the system architecture behind Tetralux-1, covering the physical layout and coordinate mapping of the six-face photodiode array, the sensor communication protocol (I2C, routed through a multiplexer), and the integration of supporting sensors with an Arduino Nano 33 IoT microcontroller. The architecture targets an average angular error of ≤10° in sun-direction estimation across a minimum of 15 test orientations, with a rolling standard deviation of ≤5° under repeated measurement. The system is designed to remain operational during sensor saturation events through fail-safe activation, and to transmit real-time telemetry at ≥95% packet reliability over continuous 30-minute operating periods. This work demonstrates that the core principles behind real-world CubeSat attitude determination and control systems (ADCS) — including coarse sun sensing, vector-based orientation estimation, and telemetry pipeline design — can be reproduced and studied through a low-cost, student-accessible engineering process, without reliance on professional laboratory infrastructure.