Covariance Analysis of the Hera Mission at the Didymos System with the Full Two-Body Problem Dynamical Model

Hera is a planetary defense space mission led by the European Space Agency (ESA), with a targeted launch in October 2024. Its primary goals encompass a thorough exploration of the Didymos binary asteroid system, marking the assessment of its internal characteristics. Additionally, Hera will meticulously analyze the results of NASA's DART mission's kinetic impactor experiment. The data gathered by Hera promises to be invaluable for any future asteroid deflection endeavors and scientific research, deepening our insights into asteroid geophysics and the evolutionary dynamics of the solar system's formation.

In this context, the precise orbit determination of Hera, along with its companion CubeSats Juventas and Milani, will enable the accurate estimation of critical physical parameters. These parameters are essential to determine the momentum enhancement resulting from the DART impact, as well as for analyzing their dynamical state, internal structure, and evolution. Key parameters include mass, mass distribution, gravity, rotational states, relative orbits, and dynamics of Didymos and Dimorphos asteroids.

The conventional approach to planetary radio science analysis, which typically treats rotational states as independent variables described by time-dependent polynomials, might not be adequate for interpreting the data collected by the Hera mission. This limitation arises primarily from the anticipated challenge posed by the spin-orbit coupling of the asteroids. Given the irregular shapes and close proximity of Dimorphos to Didymos, a more sophisticated dynamical modeling approach, like the Full Two-Body Problem (F2BP), might be necessary to accurately capture the complex dynamics of the binary system.

In this study, we present the Hera orbit determination covariance analysis employing the F2BP model within JPL's Mission Analysis, Operations, and Navigation Toolkit Environment (MONTE) orbit determination software. We show the expected sensitivity to the key scientific parameters, including the gravity field of Didymos, the relative orbit of Dimorphos, the moments of inertia of the bodies, and their rotational states. As the dynamical state of Dimorphos post-DART impact is uncertain, we explore both non-chaotic and chaotic scenarios to evaluate the results' sensitivity to varying conditions. Additionally, we conduct a comparative analysis between the F2BP outcomes and those obtained using standard radio science models.