Research On The Influence Of Aero-optical Effects On The Accuracy Of Starlight Atmospheric Refractive Index Navigation

Starlight atmospheric refraction navigation is a fully autonomous navigation technology,which has the advantages of strong anti-jamming ability,no accumulation of errors over time,and high navigation accuracy,and has been one of the hot spots of research at home and abroad.But,when an aircraft is flying at hypersonic speed,the aero-optical effect caused by the highspeed flow field blurs,offsets,energy attenuation of the star light reaching the image surface of the CCD(Charge-Coupled Device),which affects the navigation accuracy.Therefore,it is important to research on the influence of aero-optical effects on the accuracy of starlight atmospheric refractive index navigation,and the specific research contents of this paper are as follows:(1)In this paper,a three-dimensional spherical blunt cone vehicle model is established and meshed by ICEM,combined with the latest NCEP(National Centers for Environmental Prediction)reanalysis data(6 hours interval,a spatial resolution of longitude and latitude1°×1°),the atmospheric density,temperature and pressure distributions nephogram at different altitudes and speeds were simulated using FLUENT software,the influence of different receiving windows(convex,flat and concave)on the outflow field of an aircraft is analyzed.According to the hypersonic vehicle’s external flow field theory,the calculation and analysis show that the flight height and velocity of the three-dimensional spherical blunt cone vehicle both affect the distribution of the external flow field.The larger the flight speed,the more complex the flow field structure changes,while the higher the flight height,the smaller the flow field structure changes.(2)Based on the characteristics of the hypersonic vehicle’s external flow field,the influence of aero-optical effect on star light transmission is studied.First,the deflection angle,transmission path and energy decay of light at different flight speeds and altitudes are calculated according to the ray tracing method,the effect of shock deflection on star transmission is analyzed;Utilize a light tracing method based on the refractive index step size,using the refractive index step is used instead of the spatial geometry step size.This method can achieve 10-2μm is better than traditional methods in tracking accuracy,speed and accuracy of light tracing.The results show that the aerooptical effect produced by hypersonic vehicle is related to flight height and speed,the flight altitudes of 20km and 30km are taken as examples.When the flight speed is 2Ma,the angular offsets caused by the aerodynamic optical effect are 1.045"and 0.699",respectively,while when the flight speed is 10Ma,the angular offsets are 20.075"and 4.643",respectively.Therefore,aerodynamic optical effects can be ignored for aircraft at altitudes of 30km and above,but the impact of aerodynamic optical effects at 20km needs to be determined based on flight speed.(3)The propagation characteristics of star light in the far-field area extending from free space and the near-field area of complex environment near hypersonic vehicle are comprehensively analyzed,according to the principle of atmospheric refraction navigation of hypersonic vehicle starlight,a measurement equation with refraction angle as the observation model is established,The effect of aero-optical effect on navigation accuracy of hypersonic vehicle is studied using extended Kalman filter.When the aircraft flies at an altitude of 20km and a speed of 5Ma,the mean square error of the position vector and the mean square error of the velocity vector are 105.17m and 0.41m/s,respectively.