The bionic polarization navigation sensor has important research and application value in the field of modern navigation. In this study, a new algorithm for calculating the solar meridian azimuth from imaging polarization navigation sensors is proposed. By analyzing the sky polarization distribution model,there is only one line with a polarization angle of 90° in the projection plane of the sensor, and the zenith point of the sky must be on this line, with which a novel method for extracting the solar meridian in the two-dimensional projection plane is proposed. A polarization measurement model is built based on the Stokes vector method. Gaussian smoothing filtering is performed on the polarization angle image to conduct image noise suppression. The preliminary positioning of the solar meridian is solved by a dual-threshold recursive method.Then, the accuracy of the meridian detection is promoted to the sub-pixel level by interpolation to detect the exact pixel points on the solar meridian. Finally, the least-squares fitting of the precisely positioned pixels are utilized to obtain an accurate azimuth angle.An outdoor verification experiment is carried out with an imaging bionic polarization navigation sensor with a high-precision turntable system.The experimental results show that the static repeatability measurement accuracy of the algorithm is 0.0554° (σ) . The dynamic maximum error is less than 0.95° . This indicates the effectiveness and feasibility of the direction angle calculation method. The method can provide accurate and no cumulative error heading information for the movement of the carrier and provides important technical support for the field of navigation.
The star sensor is a high-precision attitude measurement device widely used in aerospace vehicles. One of the most significant influence on the accuracy of star sensor is the operating temperature. Experiments show that with the increase of temperature, the dark current noise of CMOS increases exponentially, which greatly reduces the Signal-to-Noise ratio(SNR) of the star map. A novel and efficient thermal control design is presented in this manuscript, for the purpose of keeping the temperature of CMOS and temperature fluctuation in a limited range. To validate the design, thermal analysis of the model of CMOS assemblies are built by utilizing finite element method. During orbital operation, the temperature of the optical system of the star sensor is unevenly distributed. The structural parameters such as the refractive index of the lens, the thickness of the lens, and the curvature radius will change, affecting the imaging position and energy distribution of the star point. Star point extraction and positioning accuracy will be greatly affected. These jobs could give some guidance and reference for the precise thermal control of CMOS assembly of other space optical camera.
Star tracker is the most accurate attitude sensor for satellite. Generally speaking, the higher the
accuracy, the fainter the star can be sensed by the star tracker. How to extract the faint star from a star
image is becoming a critical technology in dynamic condition for star tracker, especially using the APS
(Active Pixels Sensor) detector. A novel APS star tracker with MEMS Gyroscope aided system was
proposed in this paper that could extremely improve the detection effect and capability for the faint
stars. During the exposure time of star tracker, the trajectory of star projection on the detector maybe
occupy more than ten pixels due to the satellite rotation. In this situation, the signal-to-noise ratio will
decline sharply, and the traditional star extraction method for faint star will take no effect. As a result,
the accuracy of star tracker would decline sharply, even more, couldn’t work. Using the MEMS
Gyroscope, the track of star projection can be predicated and measured, on the basis of which the
deconvolution algorithm could be taken to recover the faint star signal. The accuracy of the star
projection centroid could be improved obviously, and the dynamic performance of the star tracker
would be improved by a magnitude. Meanwhile, the MEMS gyroscope has not less volume, mass and
power consumption, which make it more suitable for the application of APS star tracker.