On-orbit Calibration of a Telescope Alignment for Earth Observation using Stars and QUEST

The Space Robotics Laboratory at Tohoku University and the Space Mission Center at Hokkaido University have been working on the development of 50 kg-class Earth observation satellites series for more than 10 years. As one of the Earth observation instruments, we had developed a Cassegrain telescope named High-Precision Telescope (HPT). In exchange for a high ground resolution of 2.2 m, HPT has a narrow field of view (0.52 x 0.39 degrees) and the alignment error of the telescope with respect to the satellite body has a significant influence on the pointing error during Earth observation. However, in order to reduce the cost and time required to assemble the satellite, the alignment inspection and adjustment before the launch should be eliminated. In this study, we propose a method to estimate the camera alignment in three axes by using Sirius A, a first-magnitude star in the Canis Major, as a reference star for calibration. The QUEST method is applied to analyze the captured Sirius A image and ephemeris. As a result of the validation of the camera alignment matrix through Jupiter observations, the estimation error was less than 10% of the field of view, and its validity was confirmed. Compared to the conventional method using the moon images, the proposed method is superior in terms of usability and generality.