Gimbaled Spacecraft Thruster MPC Under Shared-Angle Constraints
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Solution Overview
Problem
Current spacecraft control systems face challenges in concurrently managing orbital position, attitude control, and momentum management using a single set of thrusters, particularly due to restrictions on thruster placement that can lead to unnecessary rotations and inefficiencies, and the limitations of onboard computational resources.
Innovation Solution
Implementing a model predictive control (MPC) system that optimizes a cost function over a finite receding horizon, considering hard and soft constraints on thruster angles, to control the spacecraft's position, orientation, and momentum, while allowing for torque-free thrusts when necessary and using soft constraints to penalize deviations from nominal angles, thereby improving efficiency and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thrusters are restricted in placement to avoid plume impingement on antennas and solar panels, then spacecraft components are protected from damage, but the thrusters cannot provide pure torques without applying net force, creating coupling between position and attitude control
Solution Approach 1:
The patent combines station keeping, attitude control, and momentum management into a single unified MPC control framework. Instead of treating these as separate control problems that require coordination, the invention merges them into one optimization problem that simultaneously determines thruster commands for all three objectives, eliminating the complexity of coordinating multiple control systems.
Solution Approach 2:
The MPC controller serves multiple functions simultaneously: it performs station keeping, attitude control, and momentum management all through a single control system. This multi-functional approach allows the same thruster commands to achieve multiple objectives without requiring separate dedicated systems for each function.
2Adaptability or versatility
If a single set of thrusters is used for both station keeping and momentum unloading, then the spacecraft can achieve multiple objectives with limited hardware, but coordinating these objectives concurrently becomes challenging
Solution Approach 1:
The patent merges station keeping and momentum unloading into a single unified control problem solved by MPC. The optimization framework simultaneously considers both objectives and determines thruster commands that achieve both goals concurrently, eliminating the need for complex coordination between separate control systems.
Solution Approach 2:
The MPC controller predicts future states and determines optimal thruster commands in advance over a receding horizon. By looking ahead and planning actions preliminarily, the controller can coordinate multiple objectives more effectively rather than reacting to each objective separately as they arise.
3Measurement precision
If model predictive control is implemented for autonomous spacecraft control, then station keeping and attitude control accuracy improve, but the computational burden increases significantly
Solution Approach 1:
The patent segments the control problem into manageable components within the MPC framework: the cost function is divided into multiple terms (station keeping, attitude control, momentum management), and constraints are categorized into different types. This segmentation allows the complex optimization problem to be solved more efficiently on onboard resources.
Solution Approach 2:
The patent changes parameters to reduce computational burden: it uses a finite receding horizon instead of infinite horizon, employs quadratic cost functions that enable efficient solution methods, and formulates the problem as a quadratic program that can be solved rapidly. These parameter changes maintain control accuracy while reducing computational requirements.
Data Source
AI summary
A spacecraft including a set of thrusters for changing a pose of the spacecraft. At least two thrusters mounted on a gimbaled boom assembly and are coupled together sharing the same gimbal angle. A model predictive controller (MPC) to produce a solution for controlling thrusters of the spacecraft by optimizing a cost function over a receding horizon using a model of dynamics of the spacecraft effecting a pose of the spacecraft and a model of dynamics of momentum exchange devices of the spacecraft effecting an orientation of the spacecraft. A modulator to modulate magnitudes of the thrust of the coupled thrusters determined by the MPC as pulse signals specifying ON and OFF states of each of the coupled thruster, wherein the ON states of the coupled thrusters sharing the same gimbal angle do not intersect in time. A thruster controller to operate the thrusters according to their corresponding pulse signals.