M. Navabi; M. R Akhlomadi
Volume 8, Issue 3 , October 2015, , Pages 27-40
Abstract
In this paper a nonlinear optimal control is suggested. Spacecraft intended to rendezvous and dock with the target is controlled by actuators to have a safe and stable course while satisfying requirements. The Nonlinear optimal controller is designed using nonlinear equations of relative position and ...
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In this paper a nonlinear optimal control is suggested. Spacecraft intended to rendezvous and dock with the target is controlled by actuators to have a safe and stable course while satisfying requirements. The Nonlinear optimal controller is designed using nonlinear equations of relative position and attitude of spacecraft for circular and elliptical orbits with and without reaction wheels. Cost function of the optimal control problem is expressed in the form of nonlinear quadratic regulator and control constraints are applied to the problem to gain controls in the allowable domain which is produced by the wheels. For the sake of robustness to the uncertainties as one of the most important element of the control design, nonlinear optimal control is derived using state dependent Riccatti equation based on analytical method of eigen vectors of Hamiltonian matrix. Simulation results show that this nonlinear control method achieves a good performance for rendezvous and docking problem.
Mohammad Reza Mortazavi; Ali Reza Alikhani
Volume 8, Issue 1 , April 2015, , Pages 27-41
Abstract
This paper presents a suitable technique for nonlinear control of a flexible spacecraft in proximity operations. To do proximity operations well, the pursuer spacecraft must place itself in a pre specified location relative to target and align its docking port to target’s docking port while keeping ...
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This paper presents a suitable technique for nonlinear control of a flexible spacecraft in proximity operations. To do proximity operations well, the pursuer spacecraft must place itself in a pre specified location relative to target and align its docking port to target’s docking port while keeping their attitude compatible. This procedure usually needs large, fast and accurate manoeuvres which can cause flexible structure vibrations. In addition, external disturbances, actuator saturation and model uncertainties increase difficulties of achieving such a goal. Consequently it is necessary to utilize an effective and nonlinear controller design approach to overcome these challenges. To perform considered scenario successfully, in this paper we use a method in nonlinear optimal control called State Dependent Riccati Equation (SDRE). Simple formulation and tuning as well as good performance and satisfactory robustness are some advantages of this approach in unified control of the spacecraft position, attitude and flexible motion during a proximity operation. 6DoF simulations show good performance of controller in presence of structure flexibility, parametric uncertainties, input uncertainty and saturation and external disturbance.
M. Navabi; M. Tavana; H.R. Mirzaei
Volume 7, Issue 4 , January 2015, , Pages 39-49
Abstract
Attitude control of spacecraft in order to nonlinear and high order dynamics is fundamental and challenging issue. With respect to these nonlinearities, linear control theories are not suitable choices and spacecraft may be unstable or lose performance. In this paper, State Dependent Riccati Equation ...
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Attitude control of spacecraft in order to nonlinear and high order dynamics is fundamental and challenging issue. With respect to these nonlinearities, linear control theories are not suitable choices and spacecraft may be unstable or lose performance. In this paper, State Dependent Riccati Equation (SDRE) method is utilized to 3-axis stabilization using four reaction wheels. State dependent Riccati equation method is systematic approach for optimal control of nonlinear systems which satisfies constraints of systems. In order to solve time consuming problem of this method in practical systems, Theta-D method is used. Results demonstrate the effectiveness of Theta-D in compare with Riccati method.
