Orbital Study for the Exploration of a Trojan Asteroid with a CubeSat Constellation

This study evaluates the feasibility and implications of a mission concept to explore a Trojan asteroid of Jupiter, (624) Hektor, with a CubeSat constellation. The 12U CubeSats are released from an Interplanetary Transfer Vehicle in the asteroid proximity. The mission is based on an orbital phase of one month to investigate the target asteroid with the on-board instruments. At the end of the scientific observation, the CubeSats soft-land on the asteroid, or rendezvous with the interplanetary platform. The research presents two main parts: the first one is dedicated to the study of the gravitational field of the target asteroid, which is highly inhomogeneous because of its bilobed shape. An algorithm to investigate the gravitational environment is developed, basing on the polyhedron method by R. A. Werner. The research further evaluates the dynamical characteristics of the surrounding environment by means of a pseudo-potential field, that accounts for both the complex gravitational field and the rotation of the asteroid around its axis. The study then determines the coefficients for the harmonic expansion of the gravitational field, to generate a representation that reduces computational times. In the second part, the harmonic coefficients have been used in the AGI Systems Tool Kit (STK) to propagate the trajectories of the spacecrafts, comparing different orbits and their resulting performance. The deployment of CubeSats and the month of scientific observations have been proved to be feasible by adopting a chemical thruster. Each CubeSat maintains an orbital radius in the range 290-310 km for the entire observation period thanks to the implemented correction strategy. The research continues with the study of the soft-landing by using an optimal-energy formulation, that was translated into a Two Points Boundary Value Problem (TPBVP), to determine the optimal trajectories for the soft-landing on the asteroid surface. Different initial conditions and times of flight were compared, to analyze the effect on the propellant mass consumption and required thrust level. The minimum level of thrust revealed to be at least two times the weight of the landing spacecraft on the asteroid surface. Finally, the requirements for the rendezvous of the remaining CubeSats with the ITV after the month of scientific observations were evaluated. Analytical approximations were followed by STK simulations to determine the actual consumption. The chaser vehicle can approach the ITV at less than 1 km, reaching zero relative velocity, with limited propellant consumption. Reference values for the required propellant mass and thrust level are determined for the whole mission, and deemed feasible. This study validates the feasibility of a CubeSat constellation space mission to the bilobed asteroid by providing benchmarks for the propellant consumption and guidelines for the propulsion system. The research provides a flexible framework that can be adapted to different targets, to enable a versatile exploration of remote small bodies.