Grant: Discovery Grants Program - Individual

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.**