120 research outputs found

    Extraplanetary Exploration Using Electric Solar Wind Sail

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    This doctoral research investigates the problems in the dynamics and control of extraplanetary exploration using an electric solar wind sail (E-sail). The E-sail is a novel propellantless propulsion technology that harvests energy by repelling the charged particles in solar wind. It consists of a spinning central spacecraft connected by kilometer-long and thin positively charged tethers with remote units at their tips. Three dynamic models of E-sail are developed: the high-fidelity tether dynamic model, the generalized E-sail model, and the reduced-order analytical E-sail model. The coupling effects of orbital and self-spinning motions of the E-sail, the elastic deformation of tethers, the rigid-flexible coupling effect on the attitude dynamics and spin control of E-sail, and the stability control of the flexible E-sail are thoroughly investigated based on these models. Meanwhile, the controllability of E-sail spin rate and the attitude of the E-sail are demonstrated, and the trajectory tracking problems in extraplanetary exploration missions are studied. Finally, the main contributions of this dissertation are introduced

    Extraplanetary Exploration Using Electric Solar Wind Sail

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    This doctoral research investigates the problems in the dynamics and control of extraplanetary exploration using an electric solar wind sail (E-sail). The E-sail is a novel propellantless propulsion technology that harvests energy by repelling the charged particles in solar wind. It consists of a spinning central spacecraft connected by kilometer-long and thin positively charged tethers with remote units at their tips. Three dynamic models of E-sail are developed: the high-fidelity tether dynamic model, the generalized E-sail model, and the reduced-order analytical E-sail model. The coupling effects of orbital and self-spinning motions of the E-sail, the elastic deformation of tethers, the rigid-flexible coupling effect on the attitude dynamics and spin control of E-sail, and the stability control of the flexible E-sail are thoroughly investigated based on these models. Meanwhile, the controllability of E-sail spin rate and the attitude of the E-sail are demonstrated, and the trajectory tracking problems in extraplanetary exploration missions are studied. Finally, the main contributions of this dissertation are introduced

    Coupled orbit-attitude mission design in the circular restricted three-body problem

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    Trajectory design increasingly leverages multi-body dynamical structures that are based on an understanding of various types of orbits in the Circular Restricted Three-Body Problem (CR3BP). Given the more complex dynamical environment, mission applications may also benefit from deeper insight into the attitude motion. In this investigation, the attitude dynamics are coupled with the trajectories in the CR3BP. In a highly sensitive dynamical model, such as the orbit-attitude CR3BP, periodic solutions allow delineation of the fundamental dynamical structures. Periodic solutions are also a subset of motions that are bounded over an infinite time-span (assuming no perturbing factors), without the necessity to integrate over an infinite time interval. Euler equations of motion and quaternion kinematics describe the rotational behavior of the spacecraft, whereas the translation of the center of mass is modeled in the CR3BP equations. A multiple shooting and continuation procedure are employed to target orbit-attitude periodic solutions in this model. Application of Floquet theory, Poincaré mapping, and grid search to identify initial guesses for the targeting algorithm is described. In the Earth-Moon system, representative scenarios are explored for axisymmetric vehicles with various inertia characteristics, assuming that the vehicles move along Lyapunov, halo as well as distant retrograde orbits. A rich structure of possible periodic behaviors appears to pervade the solution space in the coupled problem. The stability analysis of the attitude dynamics for the selected families is included. Among the computed solutions, marginally stable and slowly diverging rotational behaviors exist and may offer interesting mission applications. Additionally, the solar radiation pressure is included and a fully coupled orbit-attitude model is developed. With specific application to solar sails, various guidance algorithms are explored to direct the spacecraft along a desired path, when the mutual interaction between orbit and attitude dynamics is considered. Each strategy implements a different form of control input, ranging from instantaneous reorientation of the sail pointing direction to the application of control torques, and it is demonstrated within a simple station keeping scenario

    Maneuver analysis for spinning thrusting spacecraft and spinning tethered spacecraft

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    During axial thrusting of a spin-stabilized spacecraft undergoing orbital injections or control maneuvers, misalignments and center-of-mass offset create undesired body-fixed torques. The effects of the body-fixed torques, which in turn cause velocity pointing errors, can be reduced by ramping up (and then ramping down) the thruster. The first topic discussed in this thesis derives closed-form solutions for the angular velocity, Euler angles, inertial velocity, and inertial displacement solutions with nonzero initial conditions. Using the closed-form solutions, the effect of variations in the spin-axis moment of inertia and spin-rate on the spacecraft velocity pointing error are shown. The analytical solutions closely match numerical simulations. The next topic considers various ramp-up profiles (including parabolic, cosine, logarithmic, exponential, and cubic) to heuristically find a suboptimal solution to reduce the velocity pointing error. Some of the considered cosine, logarithmic, exponential, parabolic, and cubic profiles drive the velocity pointing error to nearly zero and hence qualify as effective solutions. The third topic examines a large tethered spacecraft that produces artificial gravity with the propulsion system on one end of the tether. Instead of thrusting through the center of mass, the offset thrust occurs at an angle to the tether which is held in the desired direction by changing the spin rate to compensate for decreasing propellant mass. The dynamics and control laws of the system are derived for constant, time-varying, planar, and non-planar thrust as well as spin-up maneuvers. The final topic discusses how the Bodewadt solution of a self-excited rigid body is unable to accurately predict the motion compared to a numerical integration of the equations of motion

    Conceptual design studies for large free-flying solar-reflector spacecraft

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    The 1 km diameter reflecting film surface is supported by a lightweight structure which may be automatically deployed after launch in the Space Shuttle. A twin rotor, control moment gyroscope, with deployable rotors, is included as a primary control actuator. The vehicle has a total specific mass of less than 12 g/sq m including allowances for all required subsystems. The structural elements were sized to accommodate the loads of a typical SOLARES type mission where a swam of these free flying satellites is employed to concentrate sunlight on a number of energy conversion stations on the ground

    Orbital Debris-Debris Collision Avoidance

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    We focus on preventing collisions between debris and debris, for which there is no current, effective mitigation strategy. We investigate the feasibility of using a medium-powered (5 kW) ground-based laser combined with a ground-based telescope to prevent collisions between debris objects in low-Earth orbit (LEO). The scheme utilizes photon pressure alone as a means to perturb the orbit of a debris object. Applied over multiple engagements, this alters the debris orbit sufficiently to reduce the risk of an upcoming conjunction. We employ standard assumptions for atmospheric conditions and the resulting beam propagation. Using case studies designed to represent the properties (e.g. area and mass) of the current debris population, we show that one could significantly reduce the risk of nearly half of all catastrophic collisions involving debris using only one such laser/telescope facility. We speculate on whether this could mitigate the debris fragmentation rate such that it falls below the natural debris re-entry rate due to atmospheric drag, and thus whether continuous long-term operation could entirely mitigate the Kessler syndrome in LEO, without need for relatively expensive active debris removal.Comment: 13 pages, 8 figures. Accepted for publication in Advances in Space Researc

    Technology for large space systems: A special bibliography with indexes

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    This bibliography lists 460 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1, 1968 and December 31, 1978. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design in the area of the Large Space Systems Technology (LSST) Program. Subject matter is grouped according to systems, interactive analysis and design, structural concepts, control systems, electronics, advanced materials, assembly concepts, propulsion, and flight experiments

    Multibody Dynamics and Control of Tethered Spacecraft Systems

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    This doctoral research conducts high-fidelity multiphysics modeling for tethered spacecraft systems, such as electrodynamic tether systems, electric solar wind sail systems, and tether transportation systems with climbers. Two models are developed based on nodal position finite element method. The first model deals with the tethered spacecraft system with fixed length tether, while the second model deals with the tethered spacecraft system with variable tether length using an arbitrary Lagrangian-Eulerian description. First, the nodal position finite element method is applied to model the orbital motion of tethered spacecraft systems with fixed tether length over a prolonged period. A Symplectic integration scheme is employed to attenuate the accumulation of error in the numerical analysis due to the long-term integration for tethered spacecraft systems, such as the space debris deorbit by electrodynamic tethers. A high fidelity multiphysics model is developed for electrodynamic tether systems by considering elastic, thermal, and electrical coupling effects of the tether. Most importantly, the calculation of electron collection by the electrodynamic tether is coupled with the tether libration and flexible deformation, where the orbital motion limited theory for electron collection is discretized simultaneously by the same finite element mesh used for the elastodynamic analysis of tether. The model is then used to investigate dynamics and libration stability of bare electrodynamic tethers in deorbiting end-of-mission spacecraft. Second, the model of tethered spacecraft system with fixed tether length is extended for the modeling of electric solar wind sail systems. The coupling effect of orbital and self-spinning motions of electric solar wind sail systems is investigated together with the interaction between the axial/transverse elastic motion of tether and Coulomb force. A modified throttling control algorithm is implemented in the finite element scheme to control the attitude motion of electric solar wind sail systems through the electric voltage modulation of main tethers. Third, the model of tethered spacecraft with variable tether length is applied to handle the tether length variation in tether transportation systems. The tether length variation results from the climber moving along tether and deployment and retrieval of tether at end spacecraft. The dynamic behavior of tether transportation systems with single or multiple climbers in characterized and the effectiveness of libration suppression scheme is tested by the high-fidelity model

    ALGORITHMS AND OPTIMAL CONTROL FOR SPACECRAFT MAGNETIC ATTITUDE MANEUVERS

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    This study focused on providing applicable control solutions for spacecraft magnetic attitude control system. Basically, two main lines are pursued; first, developing detumbling control laws and second, an improvement in the three-axis attitude control schemes by extending magnetic rods activation time. Spacecraft, after separation from the launching mechanism, experiences a tumbling phase due to an undesired angular momentum. In this study, we present a new efficient variant of the B-dot detumbling law by introducing a substitute of the spacecraft angular velocity, based on the ambient magnetic field data. This B-dot law preserves the orthogonality, among the applied torque, dipole moment and magnetic field vectors. Most of the existing variants of the B-dot law in the literature don\u27t preserve this orthogonality. Furthermore, the problem of minimum-time spacecraft magnetic detumbling is revisited within the context of optimal control theory. Two formulations are presented; the first one assumes the availability of the angular velocity measurements for feedback. The second formulation assumes the availability of only the ambient magnetic field measurements in the feedback; the latter is considered another optimal-based B-dot law. A reduction in detumbling time is fulfilled by the proposed laws along with less power consumption for the proposed B-dot laws. In magnetic attitude maneuvers, magnetic rods and magnetometers usually operate alternatively, to avoid the magnetic rods\u27 noise effect on magnetometers measurements. Because of that, there will be no control authority over the spacecraft during the magnetometer measurement period. Hence longer maneuver times are usually experienced. In this study, a control scheme that enables the extension of the magnetic rods’ activation time is developed, regardless of the attitude control law. The key concept is replacing the real magnetic field measurement by a pseudo measurement, which is computed based on other sensors measurements. By applying a known command to the spacecraft and measuring the spacecraft response, it is possible to compute the ambient magnetic field around the spacecraft. The system mathematical singularity is solved using the Tikhonov regularization approach. Another developed approach estimates the magnetic field, using a relatively simple and fast dynamic model inside a Multiplicative Extended Kalman Filter. A less maneuver time with less power consumption are fulfilled. These control approaches are further validated using real telemetry data from CASSIOPE mission. This dissertation develops a stability analysis for the spacecraft magnetic attitude control, taking into consideration the alternate operation between the magnetic rods and the magnetometers. It is shown that the system stability degrades because of this alternate operation, supporting the proposed approach of extending the operation time of the magnetic rods

    Integrated Optimal and Robust Control of Spacecraft in Proximity Operations

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    With the rapid growth of space activities and advancement of aerospace science and technology, many autonomous space missions have been proliferating in recent decades. Control of spacecraft in proximity operations is of great importance to accomplish these missions. The research in this dissertation aims to provide a precise, efficient, optimal, and robust controller to ensure successful spacecraft proximity operations. This is a challenging control task since the problem involves highly nonlinear dynamics including translational motion, rotational motion, and flexible structure deformation and vibration. In addition, uncertainties in the system modeling parameters and disturbances make the precise control more difficult. Four control design approaches are integrated to solve this challenging problem. The first approach is to consider the spacecraft rigid body translational and rotational dynamics together with the flexible motion in one unified optimal control framework so that the overall system performance and constraints can be addressed in one optimization process. The second approach is to formulate the robust control objectives into the optimal control cost function and prove the equivalency between the robust stabilization problem and the transformed optimal control problem. The third approach is to employ the è-D technique, a novel optimal control method that is based on a perturbation solution to the Hamilton-Jacobi-Bellman equation, to solve the nonlinear optimal control problem obtained from the indirect robust control formulation. The resultant optimal control law can be obtained in closedorm, and thus facilitates the onboard implementation. The integration of these three approaches is called the integrated indirect robust control scheme. The fourth approach is to use the inverse optimal adaptive control method combined with the indirect robust control scheme to alleviate the conservativeness of the indirect robust control scheme by using online parameter estimation such that adaptive, robust, and optimal properties can all be achieved. To show the effectiveness of the proposed control approaches, six degree-offreedom spacecraft proximity operation simulation is conducted and demonstrates satisfying performance under various uncertainties and disturbances
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