Hierarchical CMG Control for Singularity Avoidance and Torque Maximization
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Solution Overview
Problem
Existing spacecraft control moment gyroscope (CMG) systems face challenges in avoiding singularities, which can lead to undesired torque and reduced efficiency, particularly when using the 'singularity robust' inverse method, and limiting momentum volume results in wasted potential, making it difficult to achieve full attitude control while maximizing torque production.
Innovation Solution
A hierarchical two-step process is implemented to avoid singularities by determining a mandatory null space maneuver to prevent singularities and an optional maneuver to increase torque, where the mandatory maneuver is computed based on gimbal angle violations and implemented by modifying the inverse-Jacobian control matrix.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the 'singularity robust' inverse method is used to avoid singularities, then singularity avoidance is improved, but torque accuracy deteriorates due to introduced errors
Solution Approach 1:
The control strategy is segmented into two distinct components: a primary controller that ensures accurate torque production using the pseudoinverse method, and a secondary singularity avoidance controller that operates independently to maneuver CMGs away from singular configurations. This segmentation allows each controller to optimize its specific function without compromising the other.
Solution Approach 2:
A null-space motion controller acts as an intermediary between the primary torque controller and the CMG system. This intermediary computes null-space velocities that produce zero torque while maneuvering CMGs away from singularities, thereby mediating between torque accuracy requirements and singularity avoidance needs.
2Reliability
If momentum volume is limited to avoid singularities, then singularity avoidance is improved, but torque production capability deteriorates
Solution Approach 1:
The system dynamically adjusts CMG gimbal angles through null-space maneuvers to maintain operation away from singular configurations. Rather than statically limiting momentum volume, the system dynamically reconfigures the CMG array to avoid singularities while preserving full momentum envelope availability for torque production.
Solution Approach 2:
The control problem is extended from the three-dimensional torque space to a higher-dimensional space that includes null-space degrees of freedom. By utilizing this additional dimensional space, the system can maneuver away from singularities without constraining the momentum volume available for torque production in the original three-dimensional space.
3Reliability
If additional CMGs are added to provide redundancy and avoid singularities, then singularity avoidance is improved, but system complexity and weight increase
Solution Approach 1:
The control system utilizes the inherent null-space degrees of freedom provided by redundant CMGs to self-manage singularity avoidance. The hierarchical controller automatically computes and executes null-space maneuvers without requiring external intervention or complex additional hardware, allowing the system to serve its own singularity avoidance needs.
4Reliability
If null space maneuvers are used to avoid singularities, then singularity avoidance is improved, but available torque for attitude control is reduced
Solution Approach 1:
The control strategy is segmented into two distinct components: a primary controller that ensures accurate torque production using the pseudoinverse method, and a secondary singularity avoidance controller that operates independently to maneuver CMGs away from singular configurations. This segmentation allows each controller to optimize its specific function without compromising the other.
Solution Approach 2:
The hierarchical control structure ensures continuous and smooth null-space maneuvers that do not interrupt the primary torque production function. The singularity avoidance controller operates continuously in the background, making gradual adjustments to keep CMGs away from singularities without causing discontinuities or interruptions in the attitude control torque.
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
This approach effectively avoids singularities while maximizing available torque, ensuring precise control and efficient use of momentum, thereby enhancing the stability and performance of spacecraft attitude control systems.
Implementation Method 1
A CMG typically comprises a flywheel with a fixed or variable spin rate mounted to a gimbal assembly. The spin axis of the CMG can be tilted by moving the CMG using the gimbal assembly. This motion produces a gyroscopic torque orthogonal to the spin axis and gimbal axis.
Implementation Method 2
The momentum vectors of the CMGs line up such that one or more components of the requested torque can not be provided
Data Source
AI summary
A control system for adjusting the attitude of a spacecraft comprises a set of control moment gyroscopes (CMGs) configured to allow null space maneuvering. The control system further comprises a momentum actuator control processor coupled to the set of CMGs and configured to determine a mandatory null space maneuver to avoid singularities and determine an optional null space maneuver to increase available torque. The mandatory null space maneuver can be calculated based upon certain gimbal angles, and can be implemented by augmenting the inverse-Jacobian control matrix.