Adrián de Andrés, GMV; Jorge Rubio, GMV; Carlos Paulete, GMV; Diego Tirado, GMV; Ángel Gallego, GMV; Diego Escobar, GMV; Alfredo M. Antón, GMV
Keywords: Attitude determination, attitude monitoring, object characterization, photometry
Abstract:
Characterising Resident Space Objects (RSOs) is becoming increasingly important for both civil and military Space Surveillance and Tracking (SST) and Space Domain Awareness (SDA) applications. This study presents a methodology for determining and monitoring the attitude of three-axis controlled satellites with known shape and dimensions through photometric observations, making reasonable assumptions about the materials on the object’s surface and their optical reflective properties. The process is based on an Unscented Kalman Filter (UKF), which allows to estimate the satellite’s attitude evolution from a reference pointing law, through near real-time sequential processing of the photometric observations. Another algorithm, based on a Least Squares Minimisation (LSM) filter, is also presented and used to estimate the satellite’s size, using photometric observations and assuming that the shape of the object is known and its attitude follows a nominal pointing law during the observation interval. In both cases, the estimation process relies on comparing real observations with simulated observations obtained from the estimated attitude. Simulated observations are computed using a high-fidelity simulator implemented in OpenGL, which accurately calculates the reflected light contributions from each illuminated surface of the object, accounting for self-shading effects between different components.
The proposed methodology has been thoroughly validated using real photometric observations of a satellite with well-defined shape, size, and attitude, yielding highly promising results. Following this validation, the methodology is used to characterise the Russian Olymp-K-2 satellite —a geostationary communications satellite suspected of signal intelligence (SIGINT) activities— by initially estimating its size based on the approximate shape and nominal pointing law inferred from the limited public data available, and subsequently monitoring its attitude. The monitoring system employs a database to archive the outputs of each determination process and a Grafana dashboard to display the results, including thresholds, limits, and alerts, through a user-friendly graphical interface for efficient review and analysis. The results demonstrate the methodology’s promising performance in characterising and monitoring the attitude of potentially hostile or unknown satellites through the sequential processing of photometric measurements, offering a responsive and efficient means for near real-time detection of attitude changes.
Date of Conference: September 17-20, 2024
Track: Satellite Characterization