Sun sensors are mainly classified by output signal type and accuracy. Here are the major categories:
Coarse Sun Sensor (CSS)
Coarse Sun Sensors represent the most common and basic type. Engineers primarily use them for wide field-of-view and rapid solar acquisition.
They typically employ one or a few photodiodes. The output current follows the cosine law. Multiple units mounted on different faces achieve omnidirectional coverage.
– Accuracy: Generally 1° to 5°
– Field of View: Up to ±60° to ±90° or even larger
– Advantages: Extremely wide FOV, low power consumption, low cost, high reliability, and ideal for CubeSats and small satellites
– Disadvantages: Low accuracy, temperature sensitivity, sharp resolution drop near 90° incidence, and vulnerability to Earth albedo interference
Fine Sun Sensors meet high-precision attitude control demands. They serve as the current mainstream high-performance option.
They adopt quadrant photodiodes or position-sensitive detectors (PSD). The sensor precisely calculates two-dimensional angles through current differences among four quadrants. Some models use linear arrays or area-array CMOS imaging.
– Accuracy: Better than 0.1°, with high-end products reaching a few arcseconds
– Field of View: Typically ±16° to ±64°
– Advantages: Extremely high accuracy, excellent linearity, and perfect for precision pointing tasks
– Disadvantages: Small FOV, requires initial guidance from coarse sensors, higher cost, and still sensitive to albedo
Fine Sun Sensors often work together with Coarse Sun Sensors. This combination forms a “coarse-fine” two-stage attitude determination system.
Analog Sun Sensors follow a traditional classic design. They directly output continuous analog voltage/current signals.
– Working Principle: Sunlight passes through a slit and creates photocurrent distribution on dual or multiple rows of detectors. The system then computes angles through differential calculation.
– Advantages: Continuous output, strong real-time performance, and simple circuitry
– Disadvantages: Susceptible to temperature drift and noise; therefore, they require periodic on-orbit calibration
Digital Sun Sensors (DSS)
Digital Sun Sensors represent the new-generation mainstream product. They integrate CMOS or CCD image sensors with digital processing units internally.
– Working Principle: The Sun forms an image on the focal plane. The sensor calculates spot position using centroid algorithms and outputs digital angle values.
– Accuracy: Can reach below 1 arcsecond
– Advantages: High accuracy, strong radiation resistance, effectively suppresses albedo through algorithms, and can double as a simple camera
– Disadvantages: Slightly higher power consumption and data volume, plus higher cost
Other Special Types
– Sun Presence Sensor: Only outputs a binary “present/absent” signal and supports power management
– Double-cone/Pyramid Sun Sensor: Achieves multi-axis measurement through geometric structure
– MEMS Sun Sensor: Ultra-miniaturized and specially designed for nanosatellites
– Dual-head/Multi-head Sun Sensor: One electronic unit drives multiple optical heads, thus saving mass and power
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