A Spaceborne Radar-Optical Joint Localization and Measurement Scheme for Enhancing Noncooperative Spacecraft Perception

Localization and measurement of noncooperative spacecrafts in space are of great significance for on-orbit flight safety, rendezvous, and other operations. The multi-sensor fusion-based perception has gained much interest in existing space situational awareness systems, among which the radar-optical fusion is very typical. The all-day persistent detection and perception ability of the radar is complemented to the regular optical image perception. However, few methods have been explicitly reported on how to deeply fuse the radar and optical data to enhance the perception capability. This paper presents a spaceborne radar-optical joint perception scheme to enhance the situation awareness ability of the on-orbit flying spacecraft, focusing on the accurate far-range localization of the approaching spacecraft and measurement of its key components by leveraging the orthogonal observation geometry provided by the radar and camera imaging. A “one-radar, three-camera” configuration is adopted to support single-platform, co-platform and cross-platform sensing with geometric flexibility. The localization stage combines radar slant range with optical azimuth and elevation angles through a spatio-temporal synchronization. Under a 5 dB signal-to-noise (SNR), the method achieves an average relative localization error of 0.3%. For component measurement, three sensing modes are designed and fused using Dempster-Shafer theory to address illumination and range challenges: (I) radar-only, (II) co-platform radar-optical, and (III) cross-platform radar-optical. Experimental results show that under ideal conditions, the proposed system achieves length and orientation estimation errors within 3% and 2°, respectively. Even in poor lighting or far-range scenarios, radar ensures measurement reliability and improves accuracy by over 10% compared to strategies involving optical sensing. Although optical-only experiments are not performed, the proposed framework is compatible with optical-only inputs due to its modular structure.