Autonomy Challenges for Multi-Spacecraft Exploration of Interstellar Objects and Long-Period Comets
Channel: COSPAR2021 Workshops
Date: 2021-02-02

Authors: Nikhil Ranganathan, Elena Sorina Lupu, Hiroyasu Tsukamoto, Julie Castillo-Rogez, Mitch Ingham, Soon-Jo Chung

Abstract: Interstellar objects (ISOs) and long-period comets (LPCs) present intriguing opportunities for exploration.  Studying ISOs would yield key insights into the composition of other solar systems. Originating in the Oort Cloud, LPCs contain pristine records of the early solar system that are inaccessible from any other sources.  Studying these objects could help answer questions regarding the origin of water and organic material on Earth.  Exploring these "once in a lifetime", or even "once in a civilization" targets also presents unique challenges to mission design.  The short lead-time between discovery and the encounter window necessitates a rapid-response architecture that does not currently exist. Additionally, ISOs and LPCs often have extreme orbital properties, including high inclinations, and their orbital properties are not predictable.  The resulting high relative velocities and short encounter times make traditional mission architectures with large, monolithic spacecraft risky.

Swarms of small spacecraft are potential game-changers for enabling these missions. However, multi-spacecraft missions introduce new challenges, including coordination and communication between agents, task allocation, and distribution of constrained resources, such as weight and fuel.  We propose a heterogeneous multi-spacecraft approach with advanced autonomy to overcome these challenges while minimizing risk and cost.  In particular, we describe a mission concept consisting of sequential fast flybys of multiple heterogeneous spacecraft, together with an impactor spacecraft to expose the interior of the object, as pictured in the accompanying diagram.  We analyze the mission requirements that drive the need for autonomy. Autonomy is essential to ensure mission success due to the large uncertainties in the trajectories of ISOs or LPCs. In addition, should the encounter happen far from Earth, ground-in-the-loop would add extra delay to these already short encounters.

Furthermore, in the case of an LPC, risks posed by outgassing and debris could be mitigated through online, adaptive trajectory planning. In particular, AI-based autonomy requirements for such a mission would include new autonomous guidance and control strategies to maximize science return via sequential flybys.  Due to the short observation windows, mission architectures which utilize information gained from leading spacecraft to inform trailing spacecraft would greatly increase the potential science return. Other aspects include autonomous localization relative to the target, high-level autonomy for task planning, scheduling, and execution, as well as fault-tolerant autonomy. We emphasize the end-to-end autonomous guidance and control algorithms needed to ensure high science return and mission success, as well as potential swarm architectures that would enable rapid response.