First Experimental Results of Space Object Detection Using the InteRFeX Array

Abstract

This article presents the first experimental validation of InteRFeX, a nonuniform receive-only (passive) array located at the Nova Systems Space Precinct in Peterborough, Australia, designed for space domain awareness (SDA) applications. It operates over a frequency range of 70–300 MHz and is capable of functioning in a range of observational modes, including as a coherent passive bistatic radar for space surveillance, which is the focus of this work. InteRFeX exploits commercial broadcast transmissions as illuminators of opportunity (IoOs), combining cross-ambiguity function processing for bistatic range and range-rate retrieval with multiple signal classification (MUSIC)-based direction-of-arrival (DoA) estimation for angular localization. The International Space Station (ISS) serves as the experimental target, with measurements evaluated against two-line element (TLE) orbit predictions. Taking advantage of the dual-polarized array, all four reference–surveillance polarization combinations are evaluated, revealing differences in detection rate and mean signal-to-noise ratio (SNR) over the observation pass, with bistatic-range RMSEs of approximately 1-km relative to the TLE-derived reference. Independently, the MUSIC-based DoA estimates exhibit a mean angular separation of approximately 0.45° from the TLE-derived reference directions. The angular deviations are further decomposed into along-track (AT) and cross-track (CT) components, enabling a more detailed characterization of the DoA offsets relative to the TLE-derived reference trajectory. The processing framework also includes a first-order bistatic link-budget analysis to estimate the expected SNR over the observation geometry. These results demonstrate the feasibility of passive-radar SDA using radio-interferometric array technology and establish the proposed signal-processing pipeline as a basis for a dedicated coherent passive-radar mode within InteRFeX.