Closed-Loop Spacecraft Maneuver Control for Multi-Segment Trajectories
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Solution Overview
Problem
Existing spacecraft maneuvering techniques are prone to errors due to uncertainties like engine thrust variance, mass distribution, and accelerometer inaccuracies, leading to incorrect delta-V magnitude and burn duration, which are not effectively corrected in time-critical scenarios without subsequent trim burns.
Innovation Solution
A system that uses a closed-loop controller with navigation sensors like GPS, fiducial markers, and star trackers to track actual position, velocity, and acceleration, and correct for inaccuracies by executing a multi-segment planned trajectory defined by polynomial functions, allowing for real-time adjustments during the maneuver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If maximum thrust is burned until desired delta-V is achieved, then the maneuver can be completed, but errors accumulate due to thrust variance, mass variance, and off-pulsing engines
Solution Approach 1:
The patent implements a closed-loop control system that uses accelerometer feedback to continuously monitor the actual delta-V being achieved during the maneuver. The controller compares the measured acceleration against the commanded acceleration and adjusts the thrust magnitude in real-time to compensate for errors from thrust variance, mass variance, and off-pulsing engines, thereby achieving both maneuver completion and precise delta-V magnitude control
Solution Approach 2:
The system dynamically adjusts the thrust magnitude during the maneuver based on real-time feedback from accelerometers and navigation sensors. Rather than maintaining a fixed maximum thrust, the control system continuously modulates the engine output to track the desired trajectory, enabling adaptation to changing conditions while maintaining precision
2Measurement precision
If accelerometer feedback is used to measure as-executed delta-V, then measurement accuracy improves, but burn duration still executes faster or slower than predicted
Solution Approach 1:
The closed-loop control system uses accelerometer feedback not only to measure delta-V magnitude but also to infer timing errors. By continuously comparing measured acceleration against commanded acceleration and integrating over time, the system detects when the burn is executing faster or slower than predicted and adjusts thrust magnitude accordingly to correct both magnitude and timing errors simultaneously
Solution Approach 2:
The system performs preliminary correction actions during the burn by adjusting thrust magnitude in real-time based on feedback, rather than waiting for the burn to complete and then applying trim burns. This preliminary correction during execution prevents timing errors from accumulating and ensures the maneuver stays on schedule
3Manufacturing precision
If subsequent trim burns are used to reduce error, then delta-V accuracy improves, but time-critical scenarios cannot be addressed
Solution Approach 1:
The closed-loop control system continuously monitors maneuver execution and makes real-time corrections during the main burn, eliminating the need for subsequent trim burns. By detecting and correcting errors while the engines are still firing, the system achieves high delta-V accuracy without requiring additional time for post-burn trim maneuvers, thus resolving the contradiction between precision and time-critical operation
4Device complexity
If open-loop control is used with ground-based calibrations, then system complexity is reduced, but robustness against uncertainties decreases
Solution Approach 1:
The patent implements a closed-loop control system that uses feedback from accelerometers and navigation sensors to continuously monitor and correct for uncertainties such as thrust variance, mass property uncertainties, and thruster alignment errors. This feedback mechanism provides robustness against uncertainties while maintaining reasonable system complexity by using standard onboard sensors and a straightforward control algorithm
Data Source
AI summary
Techniques for maneuvering a space vehicle are presented. The techniques can include: obtaining a representation, in a computer, of a multi-segment planned position, planned velocity, and planned acceleration of the space vehicle along a planned continuous trajectory; tracking, using at least one navigation sensor, an indication of an actual position, actual velocity, and actual acceleration of the space vehicle; and maneuvering the space vehicle, using a closed-loop controller, and based on the tracking, to return to the planned position, planned velocity, and planned acceleration.