Star sensors capture star images in the sky. They use known star catalogs for star pattern identification and attitude calculation. This achieves high-precision orientation of spacecraft relative to inertial space.Angular resolution refers to the star sensor’s ability to distinguish the minimum angle between two adjacent star points. Engineers usually express it in arcseconds (“).
Angular resolution shows the optical system’s and detector’s precision in imaging stars. Higher angular resolution allows the star sensor to locate star centroids more accurately. This improves overall attitude determination precision. Typical high-precision star sensors reach sub-arcsecond levels. They even approach 0.1 arcsecond. This far exceeds the long-term accuracy of traditional gyroscopes and other inertial sensors.
Several factors influence star sensor angular resolution.
First, optical system parameters matter. Longer focal length (f) reduces the equivalent angle per pixel. Thus, it improves angular resolution. However, long focal lengths narrow the field of view (FOV). Designers must balance this with star identification needs.
Second, detector pixel size and resolution play key roles. Smaller pixel pitch increases resolution.
Third, the diffraction limit affects performance. In visible light bands, larger apertures improve resolution. Yet volume and weight constraints limit this option.
Fourth, star centroid positioning accuracy is crucial. Star sensors do not rely on single pixels for resolution. Instead, they use sub-pixel centroid extraction algorithms. Examples include the center-of-gravity method and Gaussian fitting. These achieve higher precision.
Fifth, environmental and error sources reduce effective resolution. Temperature changes cause optical distortion. Installation errors, satellite structural deformation, and stray light from the sun or Earth also interfere.
Sixth, magnitude sensitivity helps. Detecting fainter stars (higher magnitude) provides more reference stars. This increases redundancy and improves precision.
Engineers optimize the optical system. They adopt aspherical mirrors and wide-spectrum designs. These reduce distortion and chromatic aberration.
They also use large-area high-resolution detectors. These combine with back-illuminated CMOS sensors. This boosts quantum efficiency and frame rate.
Advanced algorithms deliver strong gains. Multi-level star pattern identification, event-based cameras for dynamic star extraction, and deep learning for centroid positioning all reduce noise significantly.
Satellites often carry multiple fields of view or redundant configurations. They mount 2-3 star sensors and fuse their data. This enhances overall resolution and reliability.
Precise thermal control and calibration help too. They minimize temperature gradients. In-orbit autonomous calibration compensates for errors.
Finally, miniaturization and integration advance the field. Wide field-of-view designs balance resolution with coverage. These suit micro-nano satellites well.
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TY-Space Technology (Beijing) Ltd. is professional focusing on advanced attitude optical sensors, especially Star Trackers for space industry.