星载液晶试验仪的设计和力热性能研究

Objective The nematic liquid crystal variable phase retarder (LCVR) has the advantages of a large aperture, fast modulation speed, low driving voltage, wide spectral range, lightweight, low power consumption, and no rotating structure, and it is the only low-voltage polarization modulator that can realize fast imaging and spectral observation in the solar physics research area. LCVR develops quickly in ground-based observation equipment but slowly in space applications. Alvarez-Herrero, Hou Junfeng, and others have studied the performance changes of LCVR before and after various space irradiation, as well as mechanical and thermal tests, but its performance in the spaceborne environment is still unknown. Thus, it is critical to validate its space adaptability via satellite-carrying and ground process monitoring tests. This paper describes the design and ground environment monitoring test of a set of spaceborne liquid crystal phase retardation testing instruments (hereinafter referred to as liquid crystal tester). The liquid crystal tester will carry a specific type of satellite to test the phase retardation modulation stability of the LCVR. Methods LCVR consists of liquid crystal (LC) molecules, a glass substrate with an LC holding cavity, an indium tin oxide (ITO) conductive film attached to the glass substrate's inner surface, and an oriented film (Fig. 1). The retardation of the LCVR can be continuously adjusted by changing the voltage on the ITO film (Fig. 3). The light intensity method was used to measure the retardation-voltage curve for the LC tester, considering volume, power consumption, and reliability (Fig. 2). The light source generated incident light in this optical path, which was received by the detector after passing through the collimating mirror, optic filter, polarization modulation system, and imaging mirror in turn. The normalized intensity-voltage curve can be calculated and converted into a retardation-voltage curve using polarization optics theory. Results and Discussions After the design of the flying part of the LC tester was completed (Fig. 4), the ground environment test was carried out. Before and after the mechanical test, the retardation-voltage curve of the LCVR did not change significantly (the average standard deviation (STD) < 0.1 degrees). In the thermal test, the current of the light source increased with increasing ambient temperature (-0.05 mA) (Fig. 8), but the intensity of the detector decreased (about 1 V), suggesting that the decrease in detector detection efficiency is greater than the increase in light source intensity. The retardation-voltage curve had good temperature repeatability when the LC tester was kept at the same temperature (the maximum retardation STD was 0.185 degrees). When the difference between the retardation-voltage curves at high and low temperatures was compared, the maximum difference of the thermal cycle was approximately 7.5 degrees, and that of thermal vacuum was approximately 15 degrees [Fig. 10 (a) and Fig. 10 (b)] . The difference between the predicted retardation-voltage curve and the actual curve at different ambient temperatures was less than 1 degrees using the linear compensation method. To calibrate the data over the entire temperature range, any 2 retardation-voltage curves at known ambient temperatures could be used. The normalized intensity change of the LCVR during the 9-month continuous test was 0.006, the retardation change was <1', and the means STD was 0.27 degrees (Fig. 11). Conclusions In this paper, a set of minimized liquid crystal carrying test systems is designed to validate the stability of LCVR retardation modulation in space. The flying part of the LC tester passed all mechanical and thermal tests, and the entire thermal test process was monitored. The monitoring data show that the retardation-voltage curve has good temperature repeatability when the LC tester is in the same temperature environment. The retardation-voltage curve changes linearly with ambient temperature when in different ambient temperatures, which can be used for on-orbit data calibration. After 9 months of longterm stability testing, the change in retardation is about 1 degrees, and the mean value of retardation STD is 0.27 degrees, indicating that both the liquid crystal tester and the LCVR perform well.