Ephemeris reconstruction of asteroid 65803 Didymos using astrometric and radiometric data

The planetary defense efforts reached a significant milestone with the success of NASA’s Double Asteroid Redirection Test (DART) mission. The mission effectively demonstrated the kinetic impactor technique as a viable means for asteroid deflection by impacting the DART spacecraft on Dimorphos, the minor component of the Didymos binary asteroid system. Although the impact’s effects on the mutual orbit of the asteroids have been measured, its effect on the system heliocentric orbit, described by the momentum enhancement parameter βd, is yet to be determined. Scheduled for launch on October 2024, ESA’s Hera mission aims to investigate the Didymos system in the aftermath of the DART impact, through a detailed characterization of the physical properties of the asteroids and of the impact crater. In this work, we present a reconstruction of the heliocentric trajectory of Didymos through an orbit determination process that uses currently available astrometric observations and simulated measurements from future ground-based observations, and radiometric measurements collected by the Hera mission. We find that current measurements are insufficient to estimate βd and separate its effect from other non-gravitational forces, such as the one induced by the Yarkowsky effect. Therefore, by conducting a covariance analysis, we explore the observability of βd and other critical parameters related to the non-gravitational motion. Specifically, we assess how the accuracy of such parameters is influenced by the frequency and nature of the various observations collected throughout the Hera mission, namely astrometric observations, range, and ΔDOR measurements. We show that combining range and ΔDOR observations substantially increases the signal-to-noise ratio of the estimated parameters and significantly reduces the position uncertainties on the whole estimation arc.