Study Of Contamination In Space Passive Countermeasure

The passive countermeasure is a kind of typical gentle countermeasure, of which the advantages are low technical difficulty, no fragment came into being, and low cost. In this paper, the direct spraying passive countermeasure is the object. The transport of substance in space is studied, and a model of simple lattice is set up. Then the influence of contamination on optical system is studied. This study is an important basic study.of the passive countermeasure. The influence of different size and density particles on optical system is meaningful for analyse, controllability and defending of contamination, forecasting the imaging quality, analyzing and disposal imaging quality, carrier wave choice of space nonimaging system and space defending.The key technique of the direct spraying passive coutermeasure is the velocity and the release time of substance in order to form a layer of particles near the objective optical system, which will invalidate the system.Therefore, the velocity of substance is studied firstly. Based on analysis of transportation of substance and analysis of oppositional orbit and knowledge of both orbital parameters and the time of departing from perigee, when the form of most substance arrived at optical surface is free molecular flow or quasi-free molecular flow, a spraying velocity model of substance is set up. Then the diffusing problem is analysed. The density of substance on optical system is obtained when the diffusing angle is different, according which the model of simple lattice is put forward.Accomplishment the mission by using the least substance is the goal. So, a model of simple lattice is set up, and it is studied for three instances:Firstly, particle is regarded as opaque and particles influence on imaging, of which distribution is simple lattice, is studied. According to Babinet's principle, the point spread function (PSF) can be obtained from Fraunhofer diffraction when distributing of particle is regular. After normalization, PSF on imaging plane is obtained. The characteristic of PSF is analyzed when distance between particles and size of particles are different. And the influence of density and size of particle on PSF is also obtained.Seconddly, it is supposed that the complex refractive indexes of particles are different and particles are homogeneous. FDTD (Finite-Difference Time-Domain Method) model of simple lattice is set up. Contamination influence on performance of optical system is analyzed for space imaging system and non-imaging system. Then assessment for unusable optical imaging system is work out compared FDTD results with test results. When distribution of transmitted light intensity is consistent with the assessment, relationship between radius of particulates and relevant maximum space between particulates is then obtained. So does relationship between radius of particulates and overcast proportion of particles. And relationship between radius of particulates and clearance width between particles is also obtained. Other distributions can be considered to be addition of simple lattices.At last, it is considered that particles on optical system are droplet with different size and complex refractive index inclusions. For the case of fractal droplet which satisfy Apollonian packing, forward scattering light, both the amplitude of the intensity fluctuations and polarization, is studied by FDTD. The fractal particle influence on optical system is analyzed. As for lots of droplets contaminated on optical surface, which is more serious, it can be obtained by adding the scattering light of single particle with inclusions to that of lattice.Experiment is developed on aerosol test method. The resolution is obtained when the size of particles and distance between particles on optical surface are different. The results not only prove that particle density affects imaging system more than size of particles, but also testify the assessment of unusable space optical system.