A Large-field And High Performance Star Sensor Design

At present, the star sensor is favored in high-precision attitude controlapplications; the attitude determination accuracy of the even high-precision starsensor can achieve arc second level or even higher. The CCD (Charge CoupledDevice) star sensor pictures star image by using CCD sensor, after star extraction,star identification and attitude determination, the star sensor attitude which isrelative to inertial space is calculated, thereby determining the three-axis attitudeof the aircraft.The main contents include the CCD48-20star sensor design，high refreshrate technology design and calibration method design. Details are as follows:Complete CCD48-20star sensor hardware design and driver logic design,detailing the function and design principles of the various functional modules.The star extraction of the star sensor is realized by FPGA. Image storage and starextraction are processed simultaneously. Thus, compared with the traditional starsensor, it will have better dynamic performance.High refresh rate is the development trend of star sensor, as star extraction ismore time-consuming in the whole process of attitude determination. Therefore,if they can achieve rapid real-time star image extraction, it will be conducive tothe development of the high-update-rate star sensor. The current star sensorsextract the star dot by DSP (or FPGA) after the image is stored. This way is poorreal-time and low efficiency. With the increase of the CCD area array, it isdifficult to ensure the refresh rate and dynamic performance of the star sensor. Toimprove the data update rate, this paper proposes a parallel work mode in whichthe star image storage and extraction are carried out at the same time and designsthe online star extraction algorithm. The comparative tests on CCD48-20starsensor show that the method is very effective, greatly improving the refresh rateand dynamic performance of the star sensor.There are two commonly used star sensor calibration method, namelyundetermined coefficient method and internal parameter estimation method.Undetermined coefficient method is suitable for small field (<15°×15°) starsensor calibration, with the star sensor field of view increases, the calibrationaccuracy deteriorates; while the calibration process of the inner parametersmethod is complex with a poor calibration accuracy. The field of view of the designed CCD48-20star sensor is15°×15°, in order to ensure the calibrationaccuracy of the large field star sensor. This article takes internal parameters andcalibration misalignment into account to establish internal and externalparameters calibration model. Finally, complete CCD48-20star sensorcalibration by using the undetermined coefficients method and inner/extrinsicparameters method, calibration results showed that inner/extrinsic parametersmethod has better calibration accuracy.