STARE: A self-calibrating event-based star tracker for spacecraft attitude determination with focal-length recovery

Abstract

Event cameras offer microsecond temporal resolution and high dynamic range, making them attractive for high-rate spacecraft attitude determination. However, existing event-based star-tracking methods usually rely on pre-calibrated optical parameters and cannot compensate for focal-length changes during operation. This paper presents STARE, a self-calibrating event-based star-tracking pipeline that identifies stars from raw event streams while recovering the effective focal length. STARE combines polarity-aware activity-adaptive spatiotemporal filtering, single-pass incremental clustering, and a golden-section multi-scale focal-length search for catalogue matching. In 13 laboratory recordings from a dynamic star simulator, comprising 2500 time windows acquired with an EVK4-HD event camera, STARE achieved 84.9% identification success with a mean reprojection error of 1.01 px. It recovered focal length under simulated deviations of up to ±20%, and tracking mode required approximately 1 ms per window, supporting 50 Hz attitude output. These results suggest that event-based sensing can provide calibration-tolerant attitude information for agile spacecraft.