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CALCULATION METHODS FOR IRRADIANCE COEFFICIENTS OF CYLINDRICAL SPACE OBJECT BY THE EARTH RADIATION

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The paper deals with approximate calculation methods for effective irradiance coefficients of cylindrical form space object typical for external cases of space telescopes and fragments of spacecrafts as well. There are no analytical calculation methods nowadays for integrated and effective irradiance coefficients for space objects of such configuration. Integrated irradiance coefficients define the average thermal balance on a cylindrical surface and effective ones – all over the cylinder surface taking into account its butt ends. Calculations of effective coefficients for space objects irradiance by the Earth radiation are necessary for definition of the major component of power balance – the specific power of the Earth inherent thermal radiation. Such calculations are used for determination of average temperatures of space objects. The technique is based on generalization and approximation of results for numerical calculations in the range of orbit height change from 200 km to 40000 km and also in all possible range of a tilt angle change of a cylinder axis. Uncertainties in mathematical model at small location deviations for cylinder axis from zenith-nadir line are shown. Errors of the approximate solution are analyzed during determination of integrated irradiance coefficient for a lateral cylindrical surface. The admissible total error of the received approximate solution was estimated at a temperature deviation of an object in the Earth shadow from its exact value. At the large ratios of the cylinder height to its diameter calculation, errors of integrated irradiance coefficient are maximum and can cause temperature error definitions in the Earth shadow up to 1,5 K. Errors of cylinder temperature calculation decrease with reduction of its height-to-diameter ratio. They have minimum values for a thin disk model. Temperatures calculation errors are considerably decreased for a case of cylindrical object location on the trajectory section illuminated by the Sun, and even more – at calculations of a non-stationary thermal mode. The offered calculation technique is rather accurate, simple and convenient for calculations.

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