# Spherical Polar Pattern Matching for Star Identification

## TL;DR

This paper introduces a new star identification algorithm for star sensors that is robust, efficient, and requires minimal data storage.

## Contribution

The novel spherical polar pattern matching algorithm reduces database size and improves identification speed and accuracy.

## Key findings

- The algorithm achieves 99.9% identification probability with 0.35 ms average time under moderate error conditions.
- It maintains 97.1% identification probability even when 100% of star spots are false or missing.
- The required database size is only 161 KB for a medium field of view sensor.

## Abstract

To endow a star sensor with strong robustness, low algorithm complexity, and a small database, this paper proposes an all-sky star identification algorithm based on spherical polar pattern matching. The proposed algorithm consists of three main steps. First, the guide star is rotated to be a polar star, and the polar and azimuth angles of neighboring stars are used as polar pattern elements of the guide star. Then, the relative azimuth histogram is applied to the spherical polar pattern matching, and a star pair after spherical polar pattern matching is identified through angular distance cross-verification. Finally, a reference star image is generated from the identified star pair to complete the matching process of all guide stars in the field of view. The proposed algorithm is verified by simulation experiments. The simulation results show that for a star sensor with a medium field of view (15° × 15°, 1024 × 1024 pixel) and a limiting magnitude of 6.0 Mv, the required database size is 161 KB. When false and missing star spots account for 50% of the guide stars and the star spot extraction error is 1.0 pixel, the average star identification time is 0.35 ms (@i7-4790), and the identification probability is 99.9%. However, when false and missing star spots account for 100% of the guide stars and the star spot extraction error is 5.0 pixel, the average star identification time is less than 2.0 ms, and the identification probability is 97.1%.