The Study Of Temperature Distribution And Its Effects On Image Shifting Of The Star Sensor Optics System

The temperature distribution has important effect on the accuracy performance of the high accuracy star sensor. In order to reach high accuracy, we must study the various factors which influence the temperature distribution in star sensor, which is helpful for the engineering design.At first, in this paper the emitting properties of thermal control coatings are approximately expressed by a series of rectangular spectral bands. The finite difference method is used to discrete the three-dimensional steady energy equation of circular cylindrical coordinates. The boundary condition is the radiation-conduction boundary condition and linearized. The radiative transfer factors of much reflection are solved also. And then, by programming with FORTRAN language, the temperature distribution of the lens hood is solved for several thermal control coatings. The temperature distribution of star sensor is also solved by using the software of I-DEAS. The temperature distribution functions with the solar absorptivity of the outside surface, the emissivity of the outside surface, the emissivity of the inside surface, the incident angle of sun, and the thermal conductivities of the drawtube and the filling material, are obtained respectively. In allusion to the optics system of this paper, the study shows that, to the effect of temperature difference of the optics system, there are two insensitive regions for the thermal conductivities of the drawtube and the filling material, respectively. That is, when their thermal conductivities are greater than 60 W/(m i K) and 200 W/(m i K), respectively, the effects of their thermal conductivities on temperature difference of the optics system are very small.And then, using the matrix optics theory, the formula of the star sensor's image shifting to the change of temperature of the system is deduced. According to this formula the study shows, image shifting increases with the increase in the temperature change when the average temperature of one state of the optics system changes to another one. And the study also shows that, for the optics system used in this paper, the biggest effect of the lens on image shifting are the 4th to 6th lenses. The image shifting decreases obviously when the optics system is dealt with thermal compensation measures.