| Popis: |
The subject of motion compensation techniques for aerospace applications is presented in this work. A special focus has been put on motion effects for low-light imaging applications. In order to connect the two fields of motion and imaging, a thorough introduction to each of them is given. The imaging implications caused by the described motion regimes are then derived. Before motion compensation can take place, a characterization of the motion must be established. A number of different techniques are presented, primarily based on a rotating imaging platform in a stationary scene. After motion characterization, the actual compensation can take place. Different techniques are presented including opto-mechanical stabilization, CCD based compensations and post-processing methods. Four case studies related to star-tracking, being a low-light application, are presented and possible solutions are proposed, implemented and verified:1. Star-Tracking at High Rotation Rates. Since star-tracking is based on image acquisition of stars, operation onboard a fast rotating spacecraft is facing considerable challenges. From analysis it is found that the time delayed integration is the most suitable compensation technique. The analysis, implementation and the verification are discussed. Finally, the test results are presented.2. Target Tracking. The Bering mission is presented, being a deep space vehicle targeted for a mapping of the asteroid population. It is discussed how science instruments can be aimed at the targets in the fastest and most reliable way. The representative ground tests proving the concept are described, and the obtained results are given.3. Two-Stage Star Tracking. The need for a highly accurate rotation characterization of rotating platforms surpass the performance of the most accurate star-trackers. A star-tracker system containing two optical stages is described, hereby improving the angular velocity determination accuracy by increasing the resolution and sensitivity of the star-tracking. The results from real sky tests on both a meagre and a rich star-field are presented and evaluated.4. Star-Tracker Radiation Handling. When a CCD is subjected to ionizing radiation, charges are being generated. Since this effect is highly similar to the image of a star, this effect impose a sizable challenge to star-tracking. This phenomenon is investigated and a mitigation solution is found. In-flight results from the European satellite mission SMART-1 are presented to demonstrate the performance. |
