Abstract
With the current increased widespread interest in the development and applications of micro/nanosatellites, it was found that we needed to design a small high accuracy satellite attitude determination system, because the star trackers widely used in large satellites are large and heavy, and therefore not suitable for installation on micro/nanosatellites. A Sun sensor + magnetometer is proven to be a better alternative, but the conventional sun sensor has low accuracy, and cannot meet the requirements of the attitude determination systems of micro/nanosatellites, so the development of a small high accuracy sun sensor with high reliability is very significant. This paper presents a multi-aperture based sun sensor, which is composed of a micro-electro-mechanical system (MEMS) mask with 36 apertures and an active pixels sensor (APS) CMOS placed below the mask at a certain distance. A novel fast multi-point MEANSHIFT (FMMS) algorithm is proposed to improve the accuracy and reliability, the two key performance features, of an APS sun sensor. When the sunlight illuminates the sensor, a sun spot array image is formed on the APS detector. Then the sun angles can be derived by analyzing the aperture image location on the detector via the FMMS algorithm. With this system, the centroid accuracy of the sun image can reach 0.01 pixels, without increasing the weight and power consumption, even when some missing apertures and bad pixels appear on the detector due to aging of the devices and operation in a harsh space environment, while the pointing accuracy of the single-aperture sun sensor using the conventional correlation algorithm is only 0.05 pixels.
Highlights
The sun sensor is one of the most important devices for satellites
This immunity from missing sun spots significantly improves the adaptability for a harsh space environment, and this immunity cannot be achieved by a conventional single-aperture sun sensor
The conventional single-aperture sun sensor cannot distinguish between the sun spot and noise or bad pixels, while a multi-aperture sun sensor can overcome this drawback and extend the lifetime, since both the fast multi-point MEANSHIFT (FMMS) algorithms extract and identify the sun image based on the apertures array pattern, and the immunity to the partial sun spots missing or deterioration keeps the sun sensor away from a fatal fault
Summary
The sun sensor is one of the most important devices for satellites. The early sun sensors were mainly sun appearance sensors and analog sun sensors [1]. According to the effective detection area of the Star1000 and the sun sensor FOV design h, from the Figure 3, we can find h = h2 + h3 + h4; for the specific Star1000 h3 and h4 is fixed, when the image of sunlight in the FOV is within the photosensitive surface of the detector, the greater h2 the higher accuracy. Compared with the CCD detector, APS CMOS is more suitable as a detector for a sun sensor
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