APS CMOS sensor is the core device of the whole star tracker,which directly determines the optical and electronic design of the subsequent star tracker.At present,the pixel size of industrial photosensitive detectors is relatively small,and the optical system of star trackers is large relative to the aperture and field of view,and the energy concentration of the system is poor,and the requirements of star point extraction can not be met.Therefore,a special sensor with a larger pixel size must be used.At the same time,the application of the star tracker in orbit also needs to consider the parameters such as the tolerance of high and low temperature and space radiation.
After determining the photosensitive detector,it is necessary to determine and analyze parameters such as field of view and focal length.Design the focal length parameters of the star tracker with a primary constraint of 0.1 pixel size and the accuracy index of the star tracker.The accuracy of a star tracker mainly depends on the pixel size and focal length of the sensor.In theory,the smaller the pixel size and the longer the focal length,the higher the accuracy of the star tracker and the smaller the corresponding field of view angle.
It should be noted that the above analysis is illustrated in terms of a single star.In the actual design,the field of view will reach 15 stars,and the accuracy will be improved in theory,but the error of image processing,processing,installation and calibration process is taken into account.The resulting accuracy is basically comparable to that of a single star.
Star tracker star map recognition requires a certain number of stars in the field of view.To achieve reliable star map recognition,the angular distance method contains at least 4 stars in a single field of view,while the grid method has a larger number of stars in the field of view.In order to ensure star map recognition can be achieved in any sky area pointed by the star tracker,the star tracker needs to be as sensitive as possible to the navigation stars,that is,the sensitive star magnitude should be high enough.The higher the star magnitude,the more navigation stars there are.
The greater the number of stars,the higher the accuracy of the star tracker.But as the number of stars increases,so does the amount of computation required for the system to track all the guiding stars.When the number of stars is greater than 15,the increase in the accuracy of the star tracker is not so obvious.
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TY-Space Technology (Beijing) Ltd. is professional focusing on advanced attitude optical sensors, especially Star Trackers for space industry.
