Dynamics and Control of Tethered Spacecraft Systems

系留航天器系统（TSS）是扩展航天器执行科学和其他任务能力的新型装置。其中，利用地球轨道上的电动系绳或地球轨道外的静电系绳进行无推进剂推进是替代现有火箭推进的一种有吸引力的方案。然而，TSS由于其极长的长度和可变的配置而难以操作。因此，彻底了解技术支助服务的动态和控制是任何成功的技术支助服务使命的当务之急。** TSS的高保真建模不可避免地会导致一组非线性、分布和耦合的偏微分方程。这类受随机扰动影响的系统的控制需要状态反馈。然而，内部状态沿着系绳长度是不可测量的，因为传感器只能在连接在系绳末端的航天器上使用。这导致了一个具有挑战性的反馈控制的分布式系统，只有边界观测。此外，TSS发射前控制律的实施和验证同样具有挑战性。需要新的地面试验设备和理论来将真实的TSS按比例缩小到具有有限尺寸的试验台。**该发现计划的目的是系统地研究地球轨道内外TSS的动力学和控制基础。建立在以前的发现补助金的成功，新的计算控制灵活的TSS将开发考虑多物理场，耦合的刚性-柔性动力学，轨道摄动，边界反馈控制与有限的观察边界。首先，将开发一种新的节点位置有限元卡尔曼滤波器，根据系绳末端的反馈，给出沿着系绳长度的内部状态（运动和电压）的空间和时间估计。其次，一种新的计算控制没有显式结构的TSS将开发通过结合双自适应模型预测控制与节点位置有限元卡尔曼滤波器。第三，所得到的计算控制将用于系绳部署/回收、通过电动系绳有效和高效地使空间碎片脱离轨道，以及通过电动太阳风帆进行行星际旅行。第四，将进行地面试验，以验证拟议的计算控制。最后，将在微重力条件下通过抛物线飞行对TSS的关键部件进行测试，并将在空间演示电动系缆离轨装置的原型。该发现计划将在多物理建模，耦合刚柔动力学，天体动力学，先进控制理论，空间环境，软件，硬件和实验验证方面培训HQP。HQP还将通过与合作者和团队成员的讨论、参与真实的TSS太空使命以及与航天工业的合作来接受专业发展培训。**

Tethered Spacecraft Systems (TSS) are novel devices to extend the capability of spacecraft to conduct scientific and other tasks. Among them, the propellantless propulsion by electrodynamic tethers in Earth orbits or electrostatic tethers beyond Earth orbits is an appealing alternative to existing rocket propulsion. However, TSS are difficult to operate due to their extreme long length and variable configurations. As such, a thorough understanding of dynamics and control of TSS is a preoccupation for any successful TSS mission.******High-fidelity modeling of TSS inevitably leads to a set of nonlinear, distributed and coupled partial differential equations. The control of such systems subject to stochastic perturbative effects requires feedback of states. However, interior states along tether length are not measurable as sensors are only available at spacecraft connected at tether ends. This leads to a challenging feedback control for distributed systems with only boundary observation. Furthermore, the implementation and validation of control laws for TSS before launch are equally challenging. Novel ground test facility and theory are required to scale down the real TSS into testbeds with limited dimensions.******The aim of this discovery program is to systematically study fundamentals of dynamics and control of TSS in and beyond Earth orbits. Builds on the success of previous Discovery Grant, new computational control for flexible TSS will be developed by considering multiphysics, coupled rigid-flexible dynamics, orbital perturbations, and boundary feedback control with limited observation at boundary. First, a new nodal position finite element Kalman filter will be developed to give spatial and temporal estimates of interior states (motion and electric voltage) along tether length based on feedback at tether's ends. Second, a novel computational control without explicit structures for TSS will be developed by combining a dual adaptive model predictive control with the nodal position finite element Kalman filter. Third, the derived computational control will be used for tether deployment/retrieval, effective and efficient space debris deorbit by electrodynamic tether, and interplanetary travel by electrical solar wind sail. Fourth, ground tests will be conducted to validate the proposed computational control. Finally, key components of TSS will be tested in microgravity by parabolic flights and prototype of electrodynamic tether deorbit device will be demonstrated in space.******The discovery program will train HQP in multi-physical modeling, coupled rigid-flexible dynamics, astrodynamics, advanced control theory, space environment, software, hardware, and experimental validation. HQP will also be trained in professional development through discussion with collaborators and team members, participation in real TSS space mission, and collaboration with space industry.**