Performance assessment of the Moon-Sun attitude sensor
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A preliminary feasibility study of an experimental attitude sensor, named Moon-Sun sensor, for any stabilized spacecraft, has been recently presented. This instrument, based on a low-cost CCD camera, is a moon tracker which records images in the visible spectrum. The nominal mode of operation of this instrument is to point constantly to the moon, record its images and, by means of image processing, to provide the user with redundant data for spacecraft attitude estimation. Since this sensor is able, alike the wide-FOV star trackers, to provide the user with more than one direction, it might be used in a standalone configuration and, therefore, be an essential component of an autonomous attitude determination system. At the present state of the art, there are no ideas yet about the structure and architectural solutions for this kind of sensor nor about the performances obtainable by it when a common CCD array is applied. Most of the study, in this paper, is devoted to assess the attitude accuracy obtainable by using such a sensor. We assume a complete coverage of the sky in order to ensure the functionality of the proposed instrument as independent from the spacecraft attitude. The two main features making this proposed type of instrument quite interesting are: a) its capability to be used by itself for spacecraft attitude determination, and b) its expected low cost. Even though it would provide a precision (which mainly depends on the image processing accuracies) lower than that supplied by startrackers there are, however, planned spacecraft having funding budget limitations more stringent than their attitude precision requirements. This paper presents the basic ideas and the preliminary performance assessment based on a preliminary design of the image processing software. The sensor cost is expected to be low but the more sophisticated the Moon image processing the more accurate it will be.