Satellite Attitude Control Using Eigen Vector Rotation and NDI
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Solution Overview
Problem
Existing satellite attitude control systems using linear control techniques on non-linear systems often result in oscillations, overshoots, and instability, and are inefficient in terms of energy use and time, especially when dealing with complex satellite orientations and momentum exchange.
Innovation Solution
A satellite orientation control system employing a double feedback loop with an outer loop that determines an eigen vector for rotation and an inner loop executing a non-linear dynamic inversion algorithm to control reaction wheels, enhancing stability and efficiency by directly rotating the satellite along the eigen vector and accounting for stored momentum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If linear control techniques such as PID control are applied to control satellite attitude, then the control system is simple to implement, but the system exhibits oscillations, overshoots, and instability due to the non-linear dynamics of reaction wheels
Solution Approach 1:
The patent transforms the control approach by changing the mathematical parameters and models used. Instead of linear PID control, it employs non-linear dynamic inversion based on the actual non-linear equations of motion for reaction wheels. This parameter transformation allows the controller to accurately compensate for non-linear effects while maintaining computational feasibility through systematic derivation of control torques.
Solution Approach 2:
The patent replaces the conventional linear control mechanism with a non-linear control mechanism that directly addresses the non-linear dynamics. By substituting the control law from linear PID to non-linear dynamic inversion, the system achieves stability without sacrificing implementability, as the new control law is systematically derived from first principles.
2Device complexity
If conventional attitude control systems are used, then the system structure is simple, but energy consumption is high and maneuver time is long
Solution Approach 1:
The patent introduces dynamic optimization into the control system by using non-linear dynamic inversion that adapts to the real-time state of the reaction wheels. The control torques are dynamically adjusted based on the current angular velocity, momentum, and desired attitude, allowing energy-efficient maneuvers that exploit the natural dynamics of the system rather than fighting against them.
Solution Approach 2:
The patent performs preliminary computation of the optimal control torques by deriving the non-linear dynamic inversion control law in advance. This allows the system to execute energy-efficient maneuvers without real-time iteration, as the control strategy is pre-determined based on the system dynamics and desired trajectory, reducing both computation time and energy consumption during actual maneuvers.
3Device complexity
If conventional attitude control systems are used, then the system structure is simple, but maneuver accuracy is low with significant steady-state pointing errors
Solution Approach 1:
The patent implements feedback control through non-linear dynamic inversion that continuously monitors the satellite's attitude error and adjusts control torques accordingly. The control law incorporates feedback from the current state (attitude, angular velocity) to compensate for non-linear effects and eliminate steady-state errors, achieving high pointing accuracy while maintaining a relatively simple system structure.
4Device complexity
If linear control techniques are used, then the control algorithm is simple, but the system is inefficient in terms of time and energy
Solution Approach 1:
The patent changes the control algorithm from linear to non-linear parameter transformation. By using non-linear dynamic inversion, the control system optimizes maneuver trajectories to minimize time and energy consumption while directly addressing the non-linear dynamics of reaction wheels, achieving high productivity without excessive algorithmic complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves improved stability, reduced energy consumption, and faster, more accurate satellite orientation maneuvers, minimizing steady-state pointing errors and avoiding unwanted oscillations and overshoots, as demonstrated by simulation studies.
Implementation Method 1
an inner loop receives the eigen vector or the desired body rotational rates from the outer loop as an input and executes a non-linear dynamic inversion algorithm based on the eigen vector or the desired body rotational rates to output an output signal to at least one reaction wheel of the satellite, rotating the at least one reaction wheel in response to the output signal, and orienting the satellite based upon the rotation of the at least one reaction wheel
Data Source
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AI summary
Systems and methods are described for a satellite control system that exhibits improved stability and increased efficiency by implementing a non-linear dynamic inversion inner-loop control algorithm coupled with an eigen vector outer-loop control algorithm (225). Thus, the attitude determination and control system (ADACS) may operate using commands to rotate directly about an eigen vector. Additionally, the outer-loop control system (225) includes a feed-forward control element to enhance pointing accuracy when tracking moving targets.