An **Attitude Determination and Control System (ADCS)** is the "brain and inner ear" of a spacecraft. Its electronic components work together to sense the satellite's orientation (Determination) and change it using physical actuators (Control). --- ## 1. Core Architectural Components The electronic architecture of an ADCS is typically divided into three functional categories: ### A. Sensors (Determination) These components measure external physical phenomena to calculate the spacecraft's position relative to Earth, the Sun, or stars. | Component | Function | Data Output | | :--- | :--- | :--- | | **Inertial Measurement Unit (IMU)** | Measures rotation rates and acceleration. | Angular Velocity (deg/s) | | **Star Tracker** | High-resolution camera that maps star patterns. | Quaternions/Orientation | | **Sun Sensors** | Photodiodes that detect the angle of solar light. | Sun Vector | | **Magnetometers** | Measures the Earth's magnetic field. | Magnetic Field Vector | | **GPS/GNSS Receiver** | Provides orbital position and precise timing. | Time and Coordinates | ### B. The ADCS Controller (The Computer) This is the processing hub. It runs complex algorithms (like Kalman Filters) to fuse sensor data and calculate necessary adjustments. * **Microcontrollers/FPGAs:** Often ARM-based or radiation-hardened (Rad-Hard) processors. * **Communication Bus:** Uses protocols like **I2C, SPI, or CAN bus** to talk to sensors and actuators. * **Power Management:** Regulates voltages (typically 3.3V or 5V) for sensitive sensor electronics. ### C. Actuators (Control) These are the electronic-to-mechanical interfaces that physically move the satellite. | Actuator | Electronic Mechanism | Purpose | | :--- | :--- | :--- | | **Reaction Wheels** | Brushless DC (BLDC) motors and ESCs. | Precise pointing via momentum. | | **Magnetorquers** | Electromagnetic coils driven by H-Bridges. | Desaturation and coarse pointing. | | **Thrusters** | Solenoid valves and ignition circuits. | Rapid maneuvers/Station keeping. | --- ## 2. Typical Interface Circuitry To bridge the gap between digital logic and physical sensors/actuators, several specific electronic circuits are used: ### Signal Conditioning * **ADCs (Analog-to-Digital Converters):** Converts raw voltage from analog Sun sensors or thermistors into digital data. * **Filtering:** Low-pass filters are used to remove high-frequency electrical noise from sensor lines. ### Power Electronics * **H-Bridges:** Used to reverse the polarity of current flowing through Magnetorquers, allowing the magnetic field to flip direction. * **PWM (Pulse Width Modulation):** Used to control the speed of Reaction Wheel motors with high efficiency. --- ## 3. Example Sensor Data Structure Most digital ADCS sensors communicate via standardized packets. Below is a conceptual example of a sensor reading in C-style logic: ```c struct ADCS_Data { float gyro_x; // Angular rate from IMU float gyro_y; float gyro_z; uint32_t timestamp; // Time of measurement uint8_t status; // Error codes or health bits }; ``` ---