  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 on-board 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 spacecrafts complexity but also increasing its sensitivity to
deployment maneuver errors and dynamical uncertainties. This paper introduces a
novel methodology to analyse 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
non-intrusive Chebyshev interpolation (NCI) technique, which approximates the
uncertain dynamics using a polynomial expansion, and analysing the results
using the pseudo-diffusion indicator, 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. This indicator is used here to
constrain the impact velocity and angle to values which 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 the landing success by 20 percent
and significantly reducing the landing footprint.
