Improved ephemerides for major targets of the Emirates Mission to the asteroid belt from multi-source astrometry

Abstract

Precise orbit determination of main-belt asteroids is essential for deep-space mission design, navigation, and target characterization. This study presents a refined orbit-determination analysis for 623 Chimaera and 269 Justitia, the two largest targets of the Emirates Mission to the Asteroid Belt (EMA). The dynamical model includes perturbations from sun, major planets, Pluto, selected massive asteroids, selected Kuiper Belt Objects, and solar radiation pressure. To improve computational efficiency while retaining the dominant dynamical effects, we developed a perturber-selection scheme based on a perturbing-acceleration indicator and a knee-point criterion. Long-arc ground-based optical astrometry was combined with high-precision measurements from Gaia, TESS, WISE, and stellar occultations. Catalogue-dependent debiasing, residual-based outlier rejection, and station-dependent weighting were applied to mitigate the heterogeneity of the astrometric data. The resulting solutions were evaluated using post-fit residual statistics, covariance propagation, and comparisons with reference ephemerides generated through JPL Horizons. The differences between the derived orbits and the reference ephemerides remain at the kilometre-to-tens-of-kilometres level over the investigated interval, corresponding to small angular offsets at the relevant geocentric distances. A sensitivity and covariance analysis was also conducted to assess the observability of solar radiation pressure. The results indicate that milliarcsecond-level astrometry is required for a reliable estimation of the radiation-pressure coefficient; therefore, this coefficient was fixed to its nominal theoretical value in the adopted solutions. These results provide a dynamical and observational basis for further ephemeris refinement of EMA target asteroids.