Glenn Nestell, Air Force Institute of Technology; Rachel Oliver, Air Force Institute of Technology; Francisca Parra, Air Force Institute of Technology
https://doi.org/10.64861/TIAI2823
Keywords: Space Situational Awareness (SSA), GEO, XGEO, Differential Orbit Determination, Event-Based Sensing (EBS), Optical Tracking, High-Cadence Angular Measurements, Photon-Limited Detection, Apparent Visual Magnitude, Operational Viability, Observability Limit
Abstract:
A novel sensing methodology known as event-based sensing (EBS) advances differential orbit determination (OD) techniques for space situational awareness (SSA) by enabling high-cadence, low-latency angular measurements. Unlike conventional frame-based imagers that integrate photon flux over fixed exposure intervals, event-based cameras (EBCs) asynchronously register pixel-level intensity changes, providing microsecond-scale temporal resolution while substantially reducing data throughput. This measurement paradigm enables practical implementation of differential OD algorithms such as the Advanced Uni-Sensor for Rapid Orbit Reconstruction Analysis and Sensing (AURORAS) technique. Whereas conventional optical OD methods estimate orbital states from measurements accumulated over extended observation arcs through integral formulations, AURORAS reconstructs orbital state estimates from instantaneous angular position and its time derivatives using a single observation window lasting on the order of a few minutes. However, the operational viability of event-based OD beyond the traditional GEO belt remains largely unexplored, particularly in the extended GEO (XGEO) regime, where greater orbital distances reduce photon flux and increase geometric constraints. This research investigates whether differential OD provides operationally meaningful orbit refinements for XGEO resident space objects (RSOs) and how photon availability and observation geometry jointly affect estimation performance, using commercially available ground-based optical hardware.
This work evaluates orbit refinement by tracking previously cataloged RSOs using two-line element sets (TLEs) as a priori state estimates. For each observation, AURORAS generates a differential orbit solution that is compared against the propagated TLE trajectory to quantify estimation accuracy and convergence behavior. Propagated TLE trajectories provide a consistent operational reference for both GEO and XGEO observations while supporting telescope pointing and quantitative performance assessment.
Observations employ a 14-inch Rowe-Ackermann Schmidt Astrograph (RASA) telescope equipped with a commercially available EBC and a complementary metal oxide semiconductor (CMOS) imaging sensor. The dual-sensor architecture supports differential orbit determination while independently characterizing target photometry. CMOS imagery provides astrometric calibration by identifying cataloged reference stars within the field of view (FOV). Comparing the measured signal levels of these stars with their known visual magnitudes estimates the apparent visual magnitude of each tracked RSO, allowing event-generation density to be interpreted in the context of target brightness.
The primary performance metrics include position and velocity root-mean-square (RMS) error relative to propagated TLE reference trajectories, convergence time, and normalized observation arc length. The analysis evaluates these metrics as a function of event-generation density, apparent visual magnitude, orbital distance, and apparent angular motion. As orbital distance increases, the received photon flux generally decreases, reducing event-generation density and thereby limiting the angular information available for state estimation. Simultaneously, greater range amplifies the positional uncertainty associated with a given angular measurement error, reducing the effectiveness of differential state updates even when angular precision remains unchanged. Evaluating these effects establishes how photon availability and observation geometry jointly affect estimation performance as observations extend from GEO into the XGEO regime.
This work provides a bounded performance characterization of event-based differential OD for XGEO using commercially available optical hardware. The resulting analysis identifies where differential state updates remain reliable, where measurement density becomes insufficient for robust convergence, and how photon availability and observation geometry jointly influence estimation performance. These results define practical operational boundaries as functions of apparent visual magnitude, orbital distance, event-generation density, and observation arc duration. By examining estimation performance through the lens of photon-limited and geometry-limited regimes, this research establishes a framework for assessing the operational applicability of event-based differential orbit determination in XGEO and provides guidance for integrating event-driven sensing into future ground-based SSA architectures that require rapid orbit refinement.
Date of Conference: September 15-18, 2026
Track: Astrodynamics