Optical Astrometry and Radar Ranging in Earth–Moon Tracking Geometry for Cislunar Orbit Determination of Non-Cooperative Targets

Abstract

Precise orbit determination of non-cooperative cislunar objects requires measurements that do not depend on onboard transponders or retroreflectors. This study evaluates whether optical astrometry and radar echo range can provide useful tracking performance in a two-station Earth–Moon geometry. Three configurations were tested with weighted batch least-squares estimation in the SPOT orbit-determination toolkit. Configuration A used Earth optical astrometry and Earth radar range. Configuration B added lunar optical astrometry, and Configuration C added lunar radar range. The targets were an Earth–Moon L4 case, a low circular lunar orbit, a highly elliptical lunar orbit, and an Apophis close-approach reference arc. The Earth-only baseline converged for all targets, but the benefit of a lunar station depended strongly on target distance and geometry. Lunar optical was most effective for the two lunar orbiters. Lunar radar range was most effective for distant geometries. The preferred lunar-station observable is therefore not universal. It depends on station–target distance, target dynamics, and parameter correlation.