Nicolò Bernardini

Spacecraft trajectory optimization is essential for all the different phases of a space mission, from its launch to end-of-life disposal. Due to the increase in the number of satellites and future space missions beyond our planet, increasing the level of autonomy of spacecraft is a key technical challenge. In this context, traditional trajectory optimization methods, like direct and indirect methods are not suited for autonomous or on-board operations due to the lack of guaranteed convergence or the high demand for computational power. Heuristic control laws represent an alternative in terms of computational power and convergence but they usually result in sub-optimal solutions. Successive convex programming (SCVX) enables to extend the application of convex optimization to non-linear optimal control problems. The definition of a good value of the trust region size plays a key role in the convergence of SCVX algorithms, and there is no systematic procedure to define it. This work presents an improved trust region based on the information given by the nonlinearities of the constraints which is unique for each optimization variable. In addition, differential algebra is adopted to automatize the transcription process required for SCVX algorithms. This new technique is first tested on a simple 2D problem as a benchmark of its performance and then applied to solve complex astrodynamics problems while providing a comparison with indirect, direct, and standard SCVX solutions.

Despite several missions, the origin of the two Martian moons, Phobos and Deimos, remains an open question. The goal of the next JAXA’s flagship mission Martian Moons eXploration will be to explore the two Martian moons. The satellite will be injected into a quasi-satellite orbit and it will require some station-keeping maneuvers to maintain the satellite on these orbits. Traditional methods for station-keeping around libration points are not applicable for these orbits due to their rapid evolution. In this paper we propose a new approach to perform station-keeping on periodic and quasi-periodic orbits based on convex optimization. Successive convex optimization is used to solve the time free fuel optimal problem to drive the satellite back to a reference trajectory. The latter is updated every GNC (Guidance Navigation and Control) loop by means of an innovative Discrete Fourier Transform approach that exploits the periodicity and quasi-periodicity of quasi-satellite orbits. To assess the robustness of the methodology the control and the references are computed in the autonomous dynamical model while the propagation is performed in the non-autonomous model while adding injection, orbit determination and executions errors. Monte Carlo analysis demonstrate that quasi-satellite orbits can be maintained using less than 6 m/s per month.

Understanding the solar corona and its structure, evolution and composition can provide new insights regarding the processes that control the transport of energy throughout the solar atmosphere and out into the heliosphere. However, the visible emission coming from the corona is more than a million times weaker than the emission from the photosphere, implying that direct corona observations are only possible when the disk of the Sun is fully obscured. In this paper we perform a feasibility study of a Sun occultation mission using the Earth as a natural occulter. The challenge is that the occultation zone created by the Earth does not follow a Keplerian trajectory, causing satellites placed in this region to quickly drift away from eclipse conditions. To increase the number of revisits while optimizing the propellant budget, we propose optimal trajectories in the Sun–Earth-Spacecraft circular restricted three body problem that account for scientific and engineering constraints such as limited power budget and mission duration. Chemical propulsion, electric propulsion and solar sailing configurations are compared in terms of performance and mission feasibility, revealing how 24 h of corona observations would be possible every 39 days with as little as 199 m/s of í µí»¥í µí±‰. The feasibility of the solar sail approach is hereby demonstrated, making it a challenging engineering alternative to currently available technologies.