不规则小行星附近蜂拥太阳帆相对运动研究

Most of the asteroids are characterized by irregular shape, weak gravitational field, uneven mass distribution and fast rotation rate, which give rise to enormous challenges for spacecraft carrying out a probing mission. To remove the inherent risk of single point of failure and enhance the system robustness, the current project presents a novel methodology that distributes multiple solar sail-based spacecraft around an asteroid aimed at achieving a global stable swarm via local inter-satellite information exchanges. In contrast to traditional spacecraft, the solar sail is able to exploit the natural solar radiation pressure without any propellant consumption, which is useful for long-term orbit maintenance. On the other hand, taking into account the peculiarities of swarm itself, i.e. functional decomposition, wireless connections and loose formation, the concept of solar sail swarm enables onboard system more flexible and autonomous, while the observation performance of some target regions of the asteroid is improved as well...To this end, the project first establishes the framework of the solar sail relative motion dynamics around the equilibrium point of the irregular gravitational field, and provides a thorough controllability and stability analysis of the swarm system. To account for static and dynamic communication topology respectively, distributed adaptive control strategies are proposed via a consensus concept, while considering the modeling errors of the gravitational field and the external perturbations. In particular, new artificial potential functions are adopted via swarm control algorithms, which guarantee not only a distance-bounded relative motion, but also the steady velocity consensus of the solar sail swarm system.

绝大多数小行星外形不规则、引力场微弱、质量分布不均且自转速率较快，使得航天器在执行任务时面临巨大挑战。为了从根本上消除任务的单点故障风险，增强系统鲁棒性，本项目创新性地提出将多颗太阳帆航天器分布在小行星周围，通过星间信息交互实现全局稳定的蜂拥飞行。较之传统航天器，太阳帆可以利用太阳光压产生推力且不消耗燃料，能够维持轨道的长期稳定。由于蜂拥本身具有“功能分解、无线连接、宽松编队”的技术特征，因此利用太阳帆进行蜂拥飞行不仅能够实现高度的灵活性和自主性，还可以改善对小行星特定区域的观测性能。本项目首先在不规则引力场平衡点附近建立太阳帆相对运动动力学框架，给出系统可控性和全局稳定性判据。考虑引力场建模误差和外界干扰因素，基于一致性理论分别研究静态与动态信息拓扑下太阳帆协同飞行的自适应控制策略。基于蜂拥控制算法构造合适的人工势函数，使得蜂拥太阳帆既满足距离有界性约束，又实现稳态速度的一致性。

小行星引力场高度复杂的力学环境使得探测器在执行任务时面临巨大风险。未来一些小行星协同绕飞和附着等任务需要多颗航天器集群飞行，单颗航天器已无法满足系统在鲁棒性、自主性和观测性能等方面的高要求。为此，本项目以多颗（太阳帆）航天器协同探测小行星为任务背景，围绕航天器相对小行星的悬停动力学与控制、小行星引力场内编队和集群航天器之间的相对运动等若干问题展开研究，取得了一些创新性成果：1）构建了航天器相对小行星最优悬停的理论框架；2）揭示了小行星引力场内航天器相对运动机理；3）发现了相对轨道进动速率最小的特殊相位角；4）提出了航天器编队/集群最优一致性控制方法。本项目旨在构建一套小行星引力场中航天器集群飞行动力学与控制理论体系，为我国后续小行星探测任务如何尽可能地减少不必要的燃料消耗、增强任务系统鲁棒性，进而延长整体任务寿命提供了重要的理论参考。