Abstract
Most spacecrafts are designed to be maneuvered to achieve pointing goals. This is accomplished usually by designing a three-axis control system, which can achieve arbitrary maneuvers, where the goal is to repoint the spacecraft and match a desired angular velocity at the end of the maneuver. New control laws are required, however, if one of the three-axis control actuators fails. This paper explores suboptimal maneuver strategies when only two control torque inputs are available. To handle this underactuated system control problem, the three-axis maneuver strategy is transformed to two successive independent submaneuver strategies. The first maneuver is conducted on one of the available torque axes. Next, the second maneuver is conducted on the torque available plane using two available control torques. However, the resulting control law is more complicated than the general three-axis control law. This is because an optimal switch time needs to be found for determining the end time for the single-axis maneuver or the start time for the second maneuver. Numerical simulation results are presented that compare optimal maneuver strategies for both nominal and failed actuator cases.
Highlights
This work addresses the problem of finding suboptimal spacecraft maneuver control laws for handling underactuated system, with only two control torques available
We address the problem of formulating and solving a rigorous nonlinear optimal control problem formulation for handling spacecraft maneuvers where actuator failures limit the number of control inputs to two axes
The classic spacecraft maneuver problem is generalized to handle the special case that an actuator failure alters the ω
Summary
This work addresses the problem of finding suboptimal spacecraft maneuver control laws for handling underactuated system, with only two control torques available. Many researchers have considered controlling the attitude of rigid and flexible spacecrafts when all actuators are available. Many different control strategies have been introduced for handling the nominal three-axis control case [1,2,3]. Tsiotras and Longuski [4] have considered the case designing control strategies for handling situations in which sensor and actuator failures limit the control options available for carrying out the original mission objectives. We address the problem of formulating and solving a rigorous nonlinear optimal control problem formulation for handling spacecraft maneuvers where actuator failures limit the number of control inputs to two axes. The full nonlinear set of necessary conditions is solved by introducing a multiple shooting method that is found to require ∼80 iterations for convergence
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