Lasercom Point-Ahead Angle Estimation Using Attitude Data
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Solution Overview
Problem
Lasercom systems face challenges in accurately determining the point-ahead angle for communication with mobile platforms like aircraft, as they often lack updated ephemeris data, making it difficult to precisely direct laser beams due to the finite speed of light and changing flight patterns.
Innovation Solution
A method and system that utilize attitude information and gimbal offload commands from a spacecraft's telescope subsystem, including a point-ahead determination module, to estimate the point-ahead angle, even when ephemeris data of the mobile platform is unavailable, by using initial ephemeris data of the spacecraft or its own ephemeris data for calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ephemeris data of the mobile platform is used to determine the point-ahead angle, then the accuracy of laser beam pointing is improved, but the system becomes inoperative when updated ephemeris data is unavailable
Solution Approach 1:
The patent introduces an intermediary calculation method that uses the spacecraft's own ephemeris data and attitude information as a mediator to determine the point-ahead angle when the mobile platform's ephemeris data is unavailable. This intermediary approach allows the system to maintain operability by using available data from the spacecraft itself rather than requiring the mobile platform's ephemeris data.
Solution Approach 2:
The system uses the spacecraft's own ephemeris data and attitude information to determine the point-ahead angle, rather than relying on the mobile platform's ephemeris data. This self-service approach allows the spacecraft to independently calculate the necessary pointing parameters using its own available data, ensuring continuous operation regardless of mobile platform data availability.
2Measurement precision
If the laser beam is precisely directed at the mobile platform using narrow beam width during tracking phase, then communication accuracy is improved, but the tolerable error margin is reduced to only 0.5 micro radians
Solution Approach 1:
The patent calculates the point-ahead angle in advance, accounting for the finite speed of light and the mobile platform's motion during the light travel time. This preliminary action ensures that the laser beam is already positioned to account for the platform's movement, maintaining precise pointing accuracy while the narrow beam is transmitted.
Solution Approach 2:
The system uses real-time attitude information and gimbal offload commands as feedback to continuously update and refine the point-ahead angle calculation. This feedback mechanism ensures that the narrow laser beam remains precisely directed at the mobile platform despite motion and positioning challenges.
3Reliability
If the spacecraft uses its own ephemeris data and attitude information to estimate the point-ahead angle, then system reliability is improved by ensuring operation without mobile platform ephemeris data, but additional processing of attitude information and gimbal commands is required
Solution Approach 1:
The patent makes the spacecraft's ephemeris data and attitude information serve multiple functions: they are used for both standard spacecraft operations and for determining the point-ahead angle for laser communication. This multi-functionality reduces the need for separate specialized systems and minimizes additional processing complexity.
Solution Approach 2:
The system merges the calculation of the point-ahead angle with the existing attitude determination and tracking processes. By combining these functions, the patent avoids creating separate complex processing systems and instead integrates the point-ahead calculation into the existing spacecraft operational framework.
Data Source
AI summary
Method and system for determining a point-ahead angle from a first spacecraft to a second spacecraft, each spacecraft having a laser communication (“lasercom”) terminal is provided If ephemeris data regarding the second spacecraft is unavailable to the first spacecraft while the second spacecraft is mobile, (a) obtaining attitude information regarding the first spacecraft; and (b) obtaining gimbal offload commands from a fast steering mirror and a first spacecraft telescope subsystem of the first spacecraft; wherein a point-ahead determination module receives the attitude information and the gimbal offload commands; and determining an estimate of the point-ahead angle from the first spacecraft to the second spacecraft based on the attitude information and the gimbal offload commands.