Collinear CMG Control System Singularity Avoidance
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Solution Overview
Problem
Existing spacecraft attitude control systems using control moment gyroscopes (CMGs) face challenges in avoiding singularities, which can result in incomplete torque delivery and increased system size and weight due to torque wastage, and introduce errors that steer the spacecraft in undesired directions.
Innovation Solution
A method and system for controlling sets of collinear CMGs that determine an offset for each set to guarantee a minimum three-dimensional torque, allocate total torque among sets, and calculate required gimbal movements to avoid singularities, ensuring accurate torque delivery and efficient use of momentum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pseudoinverse is used to invert the Jacobian matrix to calculate gimbal rates, then a set of possible gimbal rates can be obtained, but gimbal rates are no longer exactly mapped into the commanded torques due to introduced error, causing the spacecraft to be steered in the wrong direction and introducing significant undesired torque near singularity
Solution Approach 1:
The patent applies preliminary action by pre-calculating the offset for the momentum ellipse before singularity occurs. The offset is determined in advance to guarantee minimum three-dimensional torque capability, allowing the system to maintain accurate torque delivery even when operating near singular configurations. This proactive approach prevents the torque mapping errors that occur with pseudoinverse methods near singularity.
2Reliability
If the CMG array's momentum output is limited to a smaller area within the momentum envelope to avoid singularities, then singularity-free operation can be achieved, but potential torque is wasted and the system becomes larger and heavier than needed
Solution Approach 1:
The patent changes the parameter space by introducing an offset to the momentum ellipse, allowing the CMG array to operate closer to the boundaries of its momentum envelope without encountering singularities. This parameter transformation enables the system to utilize the full momentum capability while maintaining singularity-free operation, avoiding the need for oversized systems with reduced momentum output.
3Reliability
If additional CMGs are provided for redundancy purposes and singularity avoidance, then full attitude control can be achieved, but the system becomes larger and heavier
Solution Approach 1:
The patent transforms the control parameters by applying an offset to the momentum ellipse, which changes the operational characteristics of the CMG array. This parameter transformation allows a smaller number of CMGs to achieve full attitude control capability with redundancy, eliminating the need for additional heavy components while maintaining reliable singularity-free operation.
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 enables singularity-free movement of CMGs, ensuring that the spacecraft maintains accurate orientation control while minimizing system size and weight by optimizing torque allocation and gimbal movements.
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
A singularity can occur when the momentum vectors of the CMGs line up such that one or more components of the requested torque can not be provided.
Data Source
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AI summary
A control system (100) of a spacecraft for controlling two or more sets of collinear control moment gyroscopes (CMGs) (106) ecomprises an attitude control system (102). The attitude control system (102) is configured to receive a command to adjust an orientation of the spacecraft, determine an offset for a momentum disk (312) for each of the two or more sets of CMGs that maximizes torque, determine a momentum needed from the two or more sets of CMGs (106) to adjust the orientation of the spacecraft, and calculate a total torque needed by taking the derivative of the momentum. The control system (100) further comprises a momentum actuator control processor (104) coupled to the attitude control system (102), the momentum actuator control processor (104) configured to calculate a required gimbal movement for each of the CMGs (106) in each of the two or more sets of collinear CMGs (106) from total torque.