Objective Star sensor realizes high-precision star vector measurement or inertial attitude measurement by observing stars, which has the characteristics of high accuracy, strong anti-interference and good concealment performance. Conventional star sensors are mainly used for visible light detection. Due to the influence of sky background radiation, the star detection function can only be realized at night or outside the atmosphere. In order to meet the needs of aircraft, hot air balloons and other near-space carriers to fix the attitude and positioning under all-weather conditions, and to solve the problem of all-time star measurement by star sensors at near-space heights of 6-20 km. Aiming at the problems of small and medium field of view star sensors under all-time conditions that require multiple star observation measurements, tracking axis error has a great impact on accuracy, and large volume and weight, an optical system for all-time star measurement with large field of view at near space heights is designed.
Methods The star sensor with large field of view optical system can obtain the result of multiple star observations of the star sensor with small field, eliminating the complex tracking axis system, and has great advantages in the accuracy of star measurement, volume and weight, service life, maintainability, and reliability. When designing the optical system, it is necessary to consider the requirements of the star sensor for lightness, miniaturization and wide temperature. According to the working principle and detection ability of the star sensor, the working band of the optical system is analyzed through the atmospheric transmittance and sky background radiation at different heights. The aperture, focal length and field of view of the optical system were analyzed through the star band, number of stars, average number of detected stars, detection probability and detector characteristics, and the working band, F/#, focal length and field of the optical system was clarified. Utilizing achromatic and athermal design, N-LASF31, N-KZFS11/N-PK51, N-LAF2, N-SF66, N-LASF31, N-LASF31, N-LAK8 and other materials are used to realize a transmissive optical system with large field of view and large relative aperture transmission that can adapt to high and low temperature environments.
Results and Discussions In this paper, the design of a wide-spectrum, large field of view, and large relative aperture all-time athermalized star sensor lens is realized. The structure, the transfer function under different temperature conditions, the vertical axis chromatic aberration, the spot diagram and the distortion diagram of the optical system were analyzed, and all of them met the requirements. A star sensor prototype was built to test the optical system, and the daytime test imaging star was analyzed. The daytime multi-star detection was realized at an altitude of 3 100 m, and the 2 Mv star in the H-band could be stably detected one hour before the sun set.
Conclusions The test results show that the all-weather star sensor optical system can meet the all-weather multi-star measurement requirements of the wide-field star sensor. The optical system can be adapted to a large target surface star measuring camera to increase the field of view, further increase the number of daytime star measurement, and lower the working altitude of the star sensor. The large field of view all-weather star sensor using this optical system weighs only 1.25 kg. Compared with the all-time star sensor with a small field of view, which weighs more than 10 kg, it has a greater advantage in fitability, which will have positive significance in promoting the application of all-time star sensor technology to the near space field.
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