Singularity-Free Momentum Path for Spacecraft CMG Arrays
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Solution Overview
Problem
Existing spacecraft control moment gyroscope (CMG) systems face challenges in avoiding singularities, which occur when momentum vectors align, leading to unattainable torque components and resulting in errors that steer the spacecraft in undesired directions or require larger, heavier systems to operate within momentum envelopes.
Innovation Solution
A method and system that dynamically control the gimbal movement of collinear CMGs to rotate singularities out of the momentum path, using a dynamic control system with a momentum actuator control processor to calculate required gimbal movements and maintain a singularity-free path by employing a fixed control with a single singularity on the boundary, allowing for continuous gimbal angle control and bounded velocities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pseudoinverse method is used to calculate gimbal rates, then torque components can be calculated from the Jacobian matrix, but singularities occur when eigenvalues of AAT approach zero causing (AAT)−1 to approach infinity
Solution Approach 1:
The patent applies dynamics by making the singularity avoidance approach adaptive and time-varying. Instead of using a static pseudoinverse or fixed regularization, the system dynamically adjusts the momentum path planning based on real-time CMG configuration, predicting future singularities and proactively adjusting gimbal rates to avoid them while maintaining torque accuracy.
Solution Approach 2:
The patent implements preliminary action by predicting singularity conditions before they occur. The system continuously monitors CMG momentum vectors and calculates predicted singularity locations, allowing the control algorithm to proactively adjust gimbal rates and momentum paths before the spacecraft encounters a singularity, rather than reacting after the problem arises.
2Reliability
If (AAT)−1 is replaced by (AAT+εI)−1 to ensure it never becomes zero, then singularities are avoided, but gimbal rates are no longer exactly mapped into commanded torques introducing error ε
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the regularization parameter ε based on the current CMG configuration and proximity to singularities. Instead of using a fixed small ε value, the system adaptively modifies this parameter to maintain numerical stability while minimizing torque mapping errors, allowing larger ε when far from singularities and smaller ε when close to them.
Solution Approach 2:
The patent implements feedback by continuously monitoring the actual torque produced by the CMG array and comparing it with the commanded torque. The control algorithm uses this feedback to adjust gimbal rates in real-time, compensating for any errors introduced by regularization and ensuring accurate torque delivery while maintaining singularity avoidance.
3Reliability
If the CMG array's momentum output is limited to a smaller area within a momentum envelope, then singularities can be avoided, but potential torque is wasted and systems become much larger and heavier
Solution Approach 1:
The patent applies dynamics by enabling the CMG array to operate throughout its full momentum envelope with time-varying control strategies. The system dynamically adjusts gimbal rates and momentum distribution to navigate around singularities in real-time, allowing the spacecraft to utilize the complete torque capability of the CMG array without being constrained to a reduced momentum envelope, thereby avoiding the need for larger, heavier systems.
4Reliability
If additional CMGs are provided for redundancy purposes and singularity avoidance, then full attitude control is achieved, but device complexity increases
Solution Approach 1:
The patent applies self-service by implementing autonomous singularity avoidance control that does not require additional hardware. The control algorithm automatically monitors CMG configurations, predicts singularity conditions, and adjusts gimbal rates to maintain full attitude control capability, allowing the existing CMG array to serve itself for both primary control and singularity avoidance functions.
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 minimizing extra movement and maintaining continuous control, ensuring accurate spacecraft orientation without the need for larger systems or significant torque errors.
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 method for avoiding singularities in the movement of a set of collinear CMGs in an array of CMGs in a spacecraft is provided. First, a command to adjust an orientation of the spacecraft is received. Then, the momentum needed from the set of collinear CMGs is determined. A dynamic control that determines a momentum path and avoids singularities by rotating the singularities out of the momentum path is used and a required gimbal movement for each of the CMGs in the set of collinear CMGs from the momentum path is calculated.