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Spacecraft Control Using Magnetic Torques
Published in Yaguang Yang, Spacecraft Modeling, Attitude Determination, and Control Quaternion-based Approach, 2019
This section proposes a more attractive design method which considers as many factors as practical. The controlled attitude is aligned with LVLH frame. A general reduced quaternion model, including (a) reaction wheels, (b) magnetic torque coils, (c) the gravity gradient torque, and (d) the periodic time-varying effects of the geomagnetic field along the orbit and its interaction with magnetic torque coils, is proposed. The model is an extension of the one discussed in Chapter 4 (see also [243]). A single objective function, which considers the performance of both attitude control and reaction wheel management at the same time, is suggested. Since a well-designed periodic controller for a period system is better than constant controllers as pointed out in [48, 94], this objective function is optimized using the solution of a matrix periodic Riccati equation described earlier in this chapter, which leads to a periodic time-varying optimal control. It is shown that the design can be calculated in an efficient way and the designed controller is optimal for both the spacecraft attitude control and for the reaction wheel momentum management at the same time. A simulation test is then provided to demonstrate that the designed system achieves more accurate attitude than the optimal control system that uses only magnetic torques. Moreover, it will be shown that the designed controller based on LQR method works on the nonlinear spacecraft system.
Aerospace Controls
Published in William S. Levine, Control System Applications, 2018
M. Pachter, C. H. Houpis, Vincent T. Coppola, N. Harris McClamroch, S. M. Joshi, A. G. Kelkar, David Haessig
Gas-jet thrusters are commonly employed as actuators for spacecraft attitude control. At least 12 thrust chambers are needed to provide three-axis rotational control Each axis is controlled by two pairs of thrusters: one pair provides dock- wise moment; the other pair, counterclockwise. A thruster pair consists of two thrusters that operate simultaneously at the same thrust level but in opposite directions. They create no net force on the spacecraft but do create a moment about an axis perpendicular to the plane containing the thrust directions. Thrusters may operate continuously or in full-on, full-off modes. Although the spacecraft loses mass during thruster firings, it is often negligible compared to the mass of the spacecraft and is ignored in the equations of motion.
Linear Links and System Simulation
Published in Boris J. Lurie, Paul J. Enright, Classical Feedback Control with Nonlinear Multi-Loop Systems, 2020
Boris J. Lurie, Paul J. Enright
Matching between the signal source and the structure is provided when the signal source output mobility equals the wave mobility of the structure. Matching at either end of the structure fully damps it (since the resonances can be considered a result of interference of the waves reflected at the ends of the structure, and if at either end no reflection occurs due to matching, no resonances take place).Example 7.21A motor with motor constant k is employed to rotate a spacecraft solar panel having moment of inertia J to keep the panel perpendicular to the direction to the sun. The solar panel torsional quarter-wave resonance frequency is fr. The spacecraft attitude control can be improved by damping this resonance. This can be achieved by making the motor output mobility approximately equal to the solar panel wave mobility ρ. The desired motor output mobility can be created by compound feedback in the driver.We calculate the mobility using the voltage-to-velocity electromechanical analogy. In electrical transmission lines, the phase is 2πfx(lc)1/2, where x is the length and l and c are the inductance and capacitance per unit length. At the quarter-wave resonance, 2πfrx(lc)1/2 = π/2 wherefrom (lc)1/2 = 4xfr. Then, the wave impedance is ρ = (l/c)1/2 = 1/(4cxfr). cx is the full capacitance of the line, which is analogous to the moment of inertia J. Hence, ρ = 1/(4Jfr) and the driver output mobility is 1/(4Jk2fr).
High-order fully actuated system approaches: Part VIII. Optimal control with application in spacecraft attitude stabilisation
Published in International Journal of Systems Science, 2022
For convenience, let us simply assume that is dependent on only that is, there exists a scalar function such that In this case, instead of converting (51) into a whole system (14), we can convert (51) into two subsystems in state–space forms, as and where By now, in the Step III of Section 3, we can apply the linear quadratic regulation control technique to both systems (54) and (55) separately, as treated in the proof of Theorem 3.1. As a consequence, the initial values of the system (55) can be freely chosen, while only the initial values of the system (54) should be properly restricted to meet the feasibility of the controller (8), as treated in the proof of the above Theorem 5.3. In such a way, a much more tight subset of feasible initial values can be provided. The next section gives a demonstration of this idea with an application to spacecraft attitude control.
Robust attitude tracking control for a rigid spacecraft under input delays and actuator errors
Published in International Journal of Control, 2019
Alireza Safa, Mehdi Baradarannia, Hamed Kharrati, Sohrab Khanmohammadi
The proposed control allocation method is capable of dealing with actuator uncertainties, yet it is not ideal for spacecraft attitude control systems. The reason is that actuator constraints are not taken into account in this scheme. To deal with this problem, recall Assumption 2.5 which states that the rate constraints exist in actuators. Note that the control allocator is a part of a digital control system. Hence, we can approximate the time derivative as for i = 1, 2,… , m, where Δts is the sampling time. This allows us to rewrite the actuator constraints in Assumption 2.5 as magnitude constraints only, that is
Robust attitude tracking control of spacecraft under unified actuator dynamics
Published in International Journal of Control, 2023
When considering the actuator dynamics, the compound disturbance belongs to mismatched disturbance since the command control inputs cannot directly react to it in the same channel. This is the main difference between the attitude control of spacecraft with and without taking the actuator dynamics into consideration. As a matter of fact, when considering the actuator dynamics, the spacecraft attitude control system becomes a mismatching nonlinear system, which brings a great challenge to the spacecraft attitude control design.