Design and optimisation of orbits in proximity of asteroids using solar sails

近距离观察小行星（尤其是近地小行星，或NEAs），无论是出于科学原因（许多特征在很大程度上是未知的，小行星彼此之间非常不同），还是对行星保护和未来开采其资源（金属，水）都很重要。一种可能访问多个小行星的方法是使用太阳帆航天器。太阳帆是一种巨大的、反光的、重量轻的薄膜，它从航天器上展开，通过反射来自太阳的光子来提供推力。这很有吸引力，因为它可以在不消耗推进剂的情况下产生小而连续的加速度，从而实现高电压任务。这个小组的研究表明，太阳帆的潜力可以使任务在十年内访问多达五个近地小行星。此外，还发现了各种近地天体组合的轨迹，以及发射日期，证明了这种推进方式提供的灵活性。虽然行星际旅行是可能的，但进一步的研究挑战是如何围绕（或接近）小行星运行：该博士将研究小行星附近的动力学和轨迹，以及与行星际腿之间的转移。小行星轨道之所以具有挑战性，有几个原因：小行星是高度不规则的天体，它们的形状和密度事先不为人所知；此外，大多数都在翻滚，产生不规则和随时间变化的重力场。另一个挑战来自太阳帆的使用，它的加速度只能在一定的限制和约束下通过姿态操纵来控制。将使用多体和不规则体动力学。最初的方法很可能是基于能量水平和零速度曲线，以确保小行星附近的有界轨迹。进一步的研究将涉及数值优化，以针对最大化科学回报、可靠性和/或其他优点的特定轨迹。最终目标是设计和优化完整的轨道，从行星际阶段开始注入小行星轨道，围绕小行星运行所需的时间，并最终进入下一个行星际转移。

Close-up observations of asteroids (particularly near-Earth asteroids, or NEAs) are important both for scientific reasons (many characteristics are largely unknown today, and asteroids are very different one another), for planetary protection and for future exploitation of their resources (metals, water). A possible way to visit multiple asteroids is with a solar sail spacecraft. A solar sail is a large, reflective and lightweight membrane that is deployed from a spacecraft and provides a thrust by reflecting the photons from the sun. This is appealing because it generates a small, but continuous, acceleration over time without propellant expenditure, enabling high-v missions.Research in this group has shown the potential of solar sails to enable missions that can visit up to five near-Earth asteroids within ten years. In addition, trajectories were found for a variety of combinations of NEAs, as well as launch dates, demonstrating the flexibility offered by this type of propulsion. While the interplanetary journey is possible, a further research challenge is how to orbit around (or in proximity of) the asteroids: this PhD will investigate the dynamics and trajectories in proximity of the asteroids, together with the transfer to/from the interplanetary legs.Asteroid orbits are challenging for several reasons: asteroids are highly irregular bodies, and their shape and density are not known in advance; in addition, most are tumbling, generating an irregular and time-varying gravity field. An additional challenge comes from the use of the solar sail, whose acceleration can only be controlled, through attitude manoeuvres, within certain limits and constraints.Multi- and irregular body dynamics will be used. It is likely that an initial approach will be based on the energy levels and zero-velocity curves, to ensure bounded trajectories near the asteroid. Further research will involve numerical optimisation to target specific trajectories that maximise scientific return, reliability, and/or other merit figures. The ultimate goal is to design and optimise complete trajectories that inject into asteroid orbit starting from the interplanetary phase, orbit around the asteroid for a desired amount of time, and eventually depart into the next interplanetary transfer.