Quaternion Solution to the Problem of Optimal Control for Spacecraft’S Spatial Reorientation With Use of a Combined Quality Criterion Taking Into Account Energy Costs
Mikhail Levskii1*
1Research Institute of Space Systems, Khrunichev State Space Research-and-production Center, Korolev
*Correspondence to: Mikhail Levskii, Research Institute of Space Systems, Khrunichev State Space Research-and-production Center, Tikhonravova Street, 27, Korolev, Russia; E‑mail: levskii1966@mail.ru
Abstract
Objective: This research focuses on economically controlling spacecraft motion to minimize energy costs during reorientation. It constructs an optimal control method that considers both control forces and rotational kinetic energy, aiming for efficient spatial reorientation.
Methods: Utilizing the quaternion method and Pontryagin's maximum principle, the study devises a restricted control for optimal spacecraft turns. Analytical solutions are derived from differential equations relating orientation quaternion and angular velocity, with numerical simulations used for verification.
Results: The study presents a solution to the optimal control synthesis problem for spacecraft reorientation, optimizing for minimal energy costs. Key properties of optimal solutions are formulated analytically, aiding in determining optimal control algorithm parameters. Mathematical modeling illustrates the process and practical feasibility of the designed method for attitude control.
Conclusion: This research provides a comprehensive solution to spacecraft orientation optimal control, particularly beneficial for spacecraft equipped with electric-jet engines. The explicit control law improves efficiency and economizes spacecraft motion during orbit flight, contributing to smoother, continuous functions of time for both control functions and phase variables. The study's relevance lies in addressing the cost-effectiveness of spacecraft motion control, with potential for further research on optimal control with additional restrictions.
Keywords: spacecraft’s spatial attitude, quaternion, angular velocity, criterion of quality, maximum principle
1 INTRODUCTION
Problem of spacecraft reorientation into given angular position was solved. The solution method and the formalized description of spacecraft’s rotational motion kinematics are based on the quaternion models for description of rotational motion of solid body[1]. Spatial reorientation is a moving the spacecraft axes from one known attitude into another given angular position in finite time T. Angular attitude of spacecraft’s coordinate system is determined relative to a chosen reference basis. We considered the version of spatial turn when inertial coordinate system is reference system as often encountered case.
Much of papers have been dedicated to investigating a controlled rotation of solid body and problem of optimal control for spacecraft attitude in different statements and using different methods of solving[1-26]. For example, some authors propose the synthesis of optimal control based on the method of analytical design of optimal controllers[2], others use the concept of inverse problems of dynamics to obtain smooth controls for the implementation of the spatial rotation of the spacecraft, when the program trajectory is sought in the class of polynomials of a given degree, the coefficients of which are determined by the known values of the phase variables at the boundary points of the trajectory[3]. Special attention was paid to the problems of optimal control[2,4-24]. Optimization methods can also be different. In particular, solutions to the problem of reorientation of solid body of various configurations, based on the Pontryagin’s maximum principle, were considered in papers[9-24]. The time-optimal control is very importantly, therefore this maneuver is popular and interesting[5-12]. Other classical criteria for the quality of the control process were used previously (minimum fuel consumption[17], minimum energy consumption[12,17], etc.). Kinematic problems of rotation were considered in more detail[13-16]. Dynamic problems of optimal control are of particular interest and, at the same time, certain difficulties in solving the boundary value problem of a rotation; in some particular cases of control over a fixed time, the boundary two-point rotation problem is solved by the method of separation of variables[17]. Special regime of control for spacecraft rotation was examined also[18]. Specific features of attitude control for a spacecraft with inertial actuators (in particular, the gyrodins) have been researched earlier[25,26]. The patented method can be used in control system of a spacecraft, controlled by the gyrodins (or other inertial actuators)[27].
Earlier, planar rotations[5,8], relay controls for a turn[1,5-9,12], or the algorithms without optimization[3] for finding the smooth control functions were investigated. It is necessary to select out especially problems of the time-optimal turn[1,5-12], control problems for an axi-symmetric rigid body[10-13,18,20-22], and also kinematical problems of optimal turn[13-16]. Here, the dynamic problem of optimal control of a turn with the restricted control and the combined criterion of quality reflecting total energy costs (energy contribution of the control torques and integral costs of kinetic energy) is considered and solved in analytic form.
Analytical solution to an optimal turn problem in a closed form is of great practical interest because such solution allows the finished laws of the programmed control and variation of an optimal trajectory of spacecraft’s motion to be applied onboard. However, it is extremely difficult to obtain them for bodies (spacecrafts) with an arbitrary dynamic configuration. Some solutions (including analytical ones) were obtained for spherical[1,19] and dynamically symmetric bodies[10-13,20-22]. But analytical solution to the problem of three-dimensional turn with arbitrary boundary conditions (for angular position of a spacecraft) was not found for solid body with arbitrary distribution of mass. We know certain particular cases when general problem of a turn is solved[1,12,19]. Consequently, we can use only numerical methods (for approximate solution to this problem).
Below, we solve the problem of reorientation with new index of quality and the restricted control. In this article, the adopted functional of quality characterizes the energy costs as combination of costs of control resources and rotation energy. Its minimization is very important task in practice of spacecraft flight. For the time being, the issues of cost-effectiveness remain relevant for spacecraft motion control. A finding and investigating the optimal control of spacecraft reorientation from initial angular position into given spatial position (with respect to the chosen combined indicator) is the purpose of our research.
Optimal control problems for spacecraft orientation with use of the combined criterions of optimality were investigated earlier[21-23]. However, in contrast to the published papers, the quality criterion used by us provides smooth control functions (it is firstly) and spacecraft motion with kinetic energy of rotation which is minimum for given time of a turn (it is secondly). Additionally, in our problem of optimal reorientation, the restricted control torque acts to a spacecraft for its rotation. Also, it should be noted that solution obtained in the presented research can be applied for any type of a spacecraft (but not only for spacecrafts with inertial actuators[25,26]), in contrast to the previous researches.
4 CONCLUSION
Optimal control program of spacecraft’s reorientation with minimal costs of energy has been found; it is demonstrated that the control when angular momentum is parallel to a controlling torque within the entire interval of spatial turn is optimum. The issues of profitability and economical control of spacecraft rotations is relevant in present time, therefore the studied problem is very important. The solved problem differs from other problems with a combined functional in index form, in the presence of restrictions on the control and does not concern to an axi-symmetric body[21-23]. The obtained results demonstrate that the designed control method of spacecraft’s three-dimensional reorientation is feasible in practice.
Acknowledgements
The author would like to express greatest thanks to colleagues and specialists from Korolev Rocket Space Corporation (in Russia), and to all participants of the seminars and International conferences on optimization problems.
Conflicts of Interest
The author declared that there are no conflict of interest.
Author Contribution
Levskii M was responsible for the original draft, including methodology, validation, mathematical formulating and analysis of formulas, writing, conceptualization, supervision, numerical modeling and design of the figures that illustrated example of mathematical simulation of optimal rotation.
Abbreviation List
ERJ, Electric-rocket engines
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