Investigation and treatment of the aluminizing process for mirrors of astronomical telescopes and optical instruments of space vehicles

A model is developed to estimate the evaporation rate for aluminum of specific mass used, exploited for thin film deposition process. This model is simulated using MATLAB-SIMULINK program that represented the resistive vaporization source. A feedback temperature sensor is used with Proportional Integral (PI) controller to force the temperature gradient to acquire a trajectory suitable for the evaporation process. The simulation results showed that the temperature gradient of 45 K/s is necessary to reach the vaporization of aluminum in 20 s. Experimental results showed that current gradient of 2 A/s applied to the filament is sufficient to get temperature gradient suitable for Al melting. During the evaporation interval the current has to be constant at 50 A for 20 s in order to evaporate all Al parts. The study demonstrates that this technique will help in automating the vaporization process to avoid irregular coating reflection films on the surface of telescope and space vehicle mirrors.