Design of Robust Ballistic Landings on the Secondary of a Binary Asteroid

ESA's Hera mission aims to visit binary asteroid Didymos in late 2026, investigating its physical characteristics and the result of NASA's impact by the DART spacecraft in more detail. Two CubeSats onboard Hera plan to perform a ballistic landing on the secondary of the system, called Dimorphos. For these types of landings the translational state during descent is not controlled, reducing the spacecraft's complexity but also increasing its sensitivity to deployment maneuver errors and dynamic uncertainties. This paper introduces a novel methodology to analyze the effect of these uncertainties on the dynamics of the lander and design a trajectory that is robust against them. This methodology consists of propagating the uncertain state of the lander using the nonintrusive Chebyshev interpolation (NCI) technique, which approximates the uncertain dynamics using a polynomial expansion. The results are then analyzed using the pseudo-diffusion indicator. This indicator is derived from the coefficients of the polynomial expansion, which quantifies the rate of growth of the set of possible states of the spacecraft over time. The indicator is used here to constrain the impact velocity and angle to values that allow for successful settling on the surface. This information is then used to optimize the landing trajectory by applying the NCI technique inside the transcription of the problem. The resulting trajectory increases the robustness of the trajectory compared to a conventional method, improving landing success by 20% and significantly reducing the landing footprint.