Robust close-proximity trajectory design around small solar system bodies : application to the Hera mission.

Student thesis: Doctoral Thesis

Abstract

The exploration of small Solar System bodies is a major topic for various space programs due to their scientific potential, relevance to planetary defence, and resource utilization possibilities. Designing the spacecraft’s close proximity operations for these types of missions is extremely challenging mainly due to two factors. First, the dynamics of the spacecraft are highly complex and non-linear due to the bodies’ irregular shape and significant influence of the Solar radiation pressure. Second, the large distance to the Earth and the small size of the bodies result in difficulties in the observational process and brings about significant uncertainties in the modeling of the dynamics. Besides the uncertainty due to Earth based observations, the difficulty in navigating around an asteroid brings about uncertainties in the state of the spacecraft as well. These issues can lead to higher risk of impact with the target body, reduced scientific return, and increased planning and operational costs. This thesis presents novel methods and algorithms for the design of close-proximity orbits and trajectories around small bodies, which are capable of dealing with these issues. ESA’s Hera mission to binary asteroid Didymos is considered as a test case throughout this thesis, to show the applicability of these methods to real-life scenarios. First, two novel dynamics indicators are introduced and used to characterise the uncertain orbital dynamics around Didymos. These uncertain dynamical indicators are able to relate initial conditions to the sensitivity of the state over time to different realisation of the uncertain parameters. Maps of these indicators are made to determine the various orbits which are robust stable and thus good options for a spacecraft. Additionally, as the two CubeSats on-board Hera plan to perform a ballistic landing on Dimorphos, this thesis also develops a novel method for the robust design of these landings. The previously defined uncertain dynamics indicators are applied to this case 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 trajectory itself for minimal dispersion of the landing footprint. Finally, the very-close flyby of Dimorphos by Hera is designed by developing a technique that is able to combine the nominal trajectory design and navigation analysis steps to create a trajectory which directly takes the uncertainties and navigation performance into account. It is shown that this significantly reduces the impact risk of the flown trajectory, while obtaining long periods of good observability of Dimorphos. The results presented in this thesis regarding the robust trajectory design of the different phases of the Hera mission, show the importance of taking the uncertainties directly into consideration, and present novel algorithms that are capable of doing this efficiently. It is therefore extremely relevant for improving the performance and reducing the risks of future small Solar System body missions.
Date of Award29 Feb 2024
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorJinglang Feng (Supervisor) & Edmondo Minisci (Supervisor)

Cite this

'