Satellites play a vital role in communication, navigation, weather forecasting, and scientific research. They must precisely control their orientation and position. This is where the Attitude Determination and Control (ADC) system proves essential.star trackers is an optical sensor designed to capture star images and use them as navigation references.
The ADC system typically includes:
– Sensors: They collect data on the satellite’s position and motion.
– Actuators: Reaction wheels, thrusters, or magnetic torquers make adjustments.
– Onboard computer: It processes data and executes control algorithms.
A star tracker is an optical sensor designed to capture star images and use them as navigation references. Star trackers endure harsh space conditions: extreme temperatures, radiation, and vacuum. They operate in visible or near-infrared spectrums, focusing on fixed star patterns in the night sky.
Attitude Determination: Star trackers capture images of star fields. Algorithms identify stars by brightness and patterns, matching them to known constellations. This yields the satellite’s attitude as quaternions or Euler angles.
Error Correction: They correct drift errors accumulated over time by other sensors, like gyroscopes, caused by bias or noise.
Initialization and Recovery: After deployment or system restarts (e.g., due to solar flares), star trackers autonomously acquire attitude in “lost-in-space” mode without prior data.
Fine Pointing Support: For tasks requiring sub-arcsecond precision, like laser communication or astronomical observations, star trackers provide real-time data to the control loop.
Image Acquisition: The device points its field of view (typically 10-20 degrees) away from bright sources like the Sun, Earth, or Moon to avoid glare. It takes short exposures, often milliseconds, capturing starlight without blur from satellite motion.
Star Detection and Centroiding: Software uses edge detection and thresholding to identify bright spots (stars). Centroiding calculates the precise center of each star’s light distribution, achieving sub-pixel accuracy.
Pattern Matching: Detected star patterns are compared to an onboard database of thousands of star positions. Techniques like the Pyramid algorithm or neural networks speed up matching, even with few visible stars.
Attitude Calculation: Once matched, the system solves for the rotation matrix using least-squares optimization or quaternion estimation, aligning observed stars with catalog positions.
Integration with ADC: The calculated attitude merges with data from other sensors (e.g., via Kalman filtering) to enhance robustness. If deviations occur, ADC actuators adjust the satellite’s orientation.
This process repeats at 1-10 Hz, ensuring continuous monitoring. Advanced models include stray light baffles and radiation-hardened electronics to maintain performance in harsh environments.
Unmatched Accuracy: They achieve 1-10 arcsecond precision, surpassing sun sensors (about 0.1 degrees) or magnetometers (1 degree).
Autonomy: They require no Earth-based signals, ideal for interplanetary missions where GPS is unavailable.
Reliability: Stars are always “present,” offering a stable reference unaffected by orbital disturbances like atmospheric drag or gravitational anomalies.
Versatility: They support low Earth orbit (LEO) CubeSats, geosynchronous satellites, and deep-space missions like NASA’s Voyager or ESA’s Gaia.
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TY-Space Technology (Beijing) Ltd. is professional focusing on advanced attitude optical sensors, especially Star Trackers for space industry.
