Satellite Payload Orientation Using Onboard Orbit Error Correction
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Solution Overview
Problem
Existing satellite image acquisition systems suffer from orbit prediction errors, particularly for low and ultra-low orbiting satellites, leading to discrepancies between intended and actual imaging areas due to inaccuracies in ground-based orbit propagators, which affect mission planning and operation.
Innovation Solution
A method and satellite system that utilizes a satellite-based orbit propagator to calculate a corrected maneuvering attitude by determining a closest satellite position and time, adjusting the satellite's line-of-sight vector through a maneuvering axis and angle, using nonlinear interpolation and precision filtering to account for position errors, ensuring precise orientation towards the ground target.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ground-based orbit propagator is used for satellite orbit prediction, then mission planning can be performed, but orbit prediction errors occur leading to imaging position discrepancies
Solution Approach 1:
The patent implements a feedback mechanism where the ground station receives actual satellite position information from the satellite itself, compares it with the predicted orbit, and uses this feedback to correct the orbit prediction model. This closed-loop feedback system continuously reduces the orbit prediction error that initially limits imaging precision.
Solution Approach 2:
The patent replaces the purely ground-based mechanical orbit prediction system with a hybrid system that incorporates satellite-based autonomous orbit determination. The satellite independently calculates its own position using onboard sensors and algorithms, substituting the ground-based prediction mechanism with a self-correcting autonomous system that eliminates accumulation of prediction errors.
2Ease of operation
If ground plan imaging time is calculated based on desired satellite position, then imaging schedule can be established, but actual satellite position deviates from desired position due to orbit errors
Solution Approach 1:
The patent applies preliminary action by having the satellite pre-calculate its actual orbit position and determine the corrected imaging time before executing the imaging maneuver. The satellite autonomously adjusts the imaging schedule in advance based on its actual position, preventing the position-time mismatch from occurring in the first place rather than correcting it afterward.
Solution Approach 2:
The patent transforms the static ground-based imaging schedule into a dynamic adaptive schedule. The imaging time is no longer fixed based on predicted orbit but dynamically adjusted based on the satellite's actual real-time position. This dynamic approach allows the imaging schedule to flexibly adapt to orbital variations while maintaining operational ease.
3Measurement precision
If satellite autonomously determines closest position and corrected attitude, then imaging precision is improved, but computational complexity increases
Solution Approach 1:
The patent segments the complex orbit determination and attitude correction problem into distinct modular steps: (1) obtaining actual orbit position from onboard sensors, (2) calculating position error relative to desired position, (3) determining time to closest approach, (4) calculating corrected maneuvering attitude. This segmentation allows each module to be independently optimized and executed, reducing overall computational complexity while maintaining high precision.
Solution Approach 2:
The satellite performs preliminary calculations of the closest approach time and corrected attitude before the actual imaging maneuver. By pre-computing these parameters based on current position and velocity data, the system avoids complex real-time calculations during the critical imaging moment, reducing onboard computational burden while ensuring precision.
Data Source
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AI summary
Provided are a method and apparatus for ground target precision orientation for satellite image acquisition, in which the method includes: receiving a desired satellite position (P) for imaging from a ground station, and receiving a ground plan imaging time (T) or an algorithm execution time (TA) from the ground station, in which the ground plan imaging time (T) is calculated according to the desired satellite position (P) for imaging at a ground-based orbit propagator, and the algorithm execution time (TA) is set to be earlier than the ground plan imaging time (T) by a predetermined amount of time; and determining, based on a position error (E) calculated by using a difference between the desired satellite position (P) for imaging and the predicted satellite position (Q) output from the satellite-based orbit propagator, a closest satellite position (QC) and a closest satellite time (TC) corresponding to when the satellite is closest to the desired satellite position (P) for imaging, and determining a corrected maneuvering attitude (e,θ) for orienting the line-of-sight vector of an image capturing payload of the satellite to a ground target at the closest satellite position (QC).