Research On Key Technology Of Single-star Simulator Calibration

Star sensors are the most accurate sensors for measuring attitude information in space technology.To ensure their accuracy in orbit,high-precision ground calibration is necessary.A star simulator is an important equipment used on the ground to simulate stars in the infinite distance of the sky for testing and calibration of star sensors.With the continuous improvement of the detection and spatial resolution capabilities of star sensors,the requirements for the self-characteristics of stars simulated by star simulators are also increasing.Therefore,this paper focuses on the key technologies of calibration using a singlestar simulator,such as the imaging quality,magnitude,color temperature,and spectrum of simulated stars.To achieve high-quality star point simulation,an off-axis reflection star point simulation optical system is designed based on the technical specifications of the calibration using a single-star simulator.The structure of the off-axis reflection optical system,composed of a parabolic main mirror and a wedge half-reflective and half-transmissive secondary mirror,is determined through ZEMAX optimization design.The design results show that the distortion of the secondary mirror reflection image is less than 0.00134% with an RMS of 0.0352λ,and the distortion of the secondary mirror transmission image is less than 0.00127% with an RMS of 0.0361λ,which meets the high-quality imaging requirements of single-star simulator calibration.To further improve the position stability accuracy of the star point,a highprecision centroid positioning algorithm is used to more accurately extract the centroids of star points photographed by the collimating camera,achieving real-time monitoring of the parallelism of outgoing light and system self-collimation accuracy calibration.To achieve stable spectral output of the light source,LEDs and xenon lamps are selected as light sources,and an integrating sphere is used for light mixing.The uniformity of LED irradiation and light flux is analyzed,and a Tracpro simulation is used to analyze the irradiance uniformity of the light source at the output of the integrating sphere.The arrangement of the light source in the integrating sphere is determined through simulation to match the star point simulation optical system.The simulation results show that after suppressing stray light,the non-uniformity of single-star simulator irradiation is about 1.2%.To achieve high-precision fitting of spectral curves of simulated star points under different color temperatures,a spectral model is established by mixing xenon lamps with multiple peak-wavelength LEDs and matching with a standard target spectrum.The algorithm for solving the spectrum is changed from the traditional genetic algorithm to an intelligent evolutionary algorithm with better crossover and mutation probabilities.The MATLAB software is used to simulate and analyze the spectral curve,which can accurately obtain the types and number of LEDs required.The simulation results show that the maximum matching error of the spectral curve under different color temperatures is about7.86%.To achieve the simulation of star points of 2Mv-8Mv under different color temperatures,an energy transmission model for star magnitude is established to determine the energy required for the mixed light source.The star point simulation optical system is adjusted using pulse width modulation(PWM)dimming and filter replacement to achieve high-precision simulation of star points with certain spectral distributions,color temperatures,and magnitudes.The simulation results show that the maximum relative error of the star magnitude simulation is about 5.58%,with an absolute error of 0.09 Mv.Finally,a system experimental platform was constructed,and corresponding testing equipment and methods were provided to test the design specifications related to the calibration using a single-star simulator.The test results show that the optical system focal length is greater than or equal to 3000 mm,and the wavefront error of the star point simulation optical system is better than λ/20.The parallelism of outgoing light is better than 1″,and the Autocollimation accuracy is better than 0.5″.In the light source system,the stability of the light source system is better than 3%,and the non-uniformity of the light beam irradiation is better than ±5%.At color temperatures of 2700 K,3900K,5500 K,6800K,8500 K,and15000K,the spectral matching error is better than ±8%.The maximum relative error of the star magnitude simulation is better than ±6%,and the absolute error is better than 0.1Mv in the range of 2Mv-8Mv.