Spacecraft Eigenmotion Control for Fuel-Efficient Halo Orbit Keeping
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Solution Overview
Problem
The deployment of spacecrafts near unstable orbits, such as the Lunar Orbital Platform-Gateway in a highly elliptical seven-day near-rectilinear halo orbit around the Moon, faces challenges due to navigational uncertainties and unpredictable disturbance forces, leading to rapid divergence from computed trajectories, which requires frequent and fuel-consuming control actions.
Innovation Solution
A control policy utilizing linear approximations of spacecraft dynamics and local modal decompositions of state transition matrices to identify special states with non-diverging natural motion, allowing the spacecraft to operate within a desirable subspace near the reference trajectory, reducing the need for continuous control and minimizing fuel consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional high-fidelity trajectory methods are used to account for all major predictable forces, then trajectory accuracy is improved, but fuel consumption increases due to frequent stabilizing control actions
Solution Approach 1:
The patent applies self-service by allowing the spacecraft to utilize its own natural motion characteristics to maintain trajectory accuracy. The control system identifies and exploits stable manifold directions where the spacecraft can passively maintain position without continuous fuel consumption, effectively using the spacecraft's inherent dynamics to serve the stabilization function that would otherwise require active fuel-based control.
Solution Approach 2:
The patent changes the control parameter from continuous fuel-based thrust to discrete manifold-following trajectories. By transforming the control approach from active force application to passive geometric trajectory following along stable manifolds, the system achieves trajectory accuracy without the continuous energy consumption associated with conventional stabilization methods.
2Stability of the object's composition
If continuous fuel-based control is applied to maintain spacecraft on trajectory, then trajectory stability is improved, but operational complexity increases
Solution Approach 1:
The patent replaces the mechanical fuel-based thrust system with a geometric trajectory-following approach. Instead of using continuous fuel combustion to counteract perturbations, the control system computes and follows stable manifold trajectories that naturally guide the spacecraft along the desired path, substituting mechanical force application with geometric guidance based on the spacecraft's natural motion characteristics.
Solution Approach 2:
The patent employs periodic computation and execution of manifold-following trajectories rather than continuous control. The system periodically updates the stable manifold computation and executes trajectory segments, creating a periodic control rhythm that maintains stability while reducing the operational complexity compared to continuous fuel-based stabilization.
3Manufacturing precision
If multiple shooting or collocation-based techniques are used for high-fidelity trajectory, then trajectory precision is improved, but computational expense increases
Solution Approach 1:
The patent applies preliminary action by pre-computing the stable and unstable manifolds for the desired trajectory before actual spacecraft operation. These manifolds are calculated in advance using the spacecraft's dynamic model, allowing the real-time control system to simply follow the pre-computed geometric paths rather than performing complex multiple shooting or collocation computations during operation, thus reducing online computational complexity while maintaining precision.
Data Source
AI summary
A computer-implemented method for maintaining a spacecraft near an orbit comprises steps of detecting that a distance from the spacecraft to the orbit is greater than a spacecraft threshold and in response, linearizing dynamics of the spacecraft from a current time over a time horizon with respect to a high-fidelity reference trajectory to produce a state transition matrix (STM) for an uncontrolled motion of the spacecraft within the time horizon. The STM includes non-expanding eigenvectors with magnitudes less than or equal to one and expanding eigenvectors with magnitudes greater than one. The method further comprises determining a control action that changes an upcoming state of the spacecraft to a linear combination of the non-expanding eigenvectors of the STM and generating a control command to an actuator of the spacecraft.