Effect of 2-D Turntable Pointing Performance of a Moon-Based Sensor on Geolocation Accuracy

Abstract

A Moon-based sensor offers a unique view for continuous Earth observation. The 2-D turntable’s pointing performance is a critical factor influencing geolocation accuracy. The vast distance between the Earth and the Moon amplifies minor pointing errors of the turntable into significant geolocation inaccuracy. By establishing a geometric model, an analytic expression of Earth’s trajectory from the Moon-based view is derived. Three critical issues are discussed: 1) the Earth’s 18.6-year trajectory forms a $16^{\circ } \times 14^{\circ }$ envelope, which determines the observation range for the sensor. The rotation angle and position of the envelope vary at different lunar locations, while its size and shape remain consistent; 2) geolocation errors caused by temporal interval vary periodically with a half-sidereal month cycle and can be compensated by calculating Earth’s velocity, while errors due to the step angle show irregular oscillations. Without calibration, both parameters can introduce geolocation errors on the scale of hundreds of kilometers. Reducing both parameters can significantly improve geolocation accuracy; and 3) even with optimization of both parameters, the geolocation accuracy cannot be reduced to within a single pixel. To achieve geolocation accuracy within design requirements, it is necessary to not only optimize these two factors but also adopt additional measures to improve precision. All these insights will inform the parameter optimization and design of the Moon-based sensor for future applications.