Practical relations for assessments of the gas coma parameters

To ensure the safety of a spacecraft and efficiency of the instrument operations it is indispensable to have simple (i.e. with minimal number of parameters and which does not require long time simulations) models for the assessments of the dusty-gas coma. A dusty-gas flow from cometary nucleus preserves common general structure regardless the features of a particular comet. Therefore, elementary models which account only for the main factors affecting the dusty-gas motion could be used for rough estimations of such characteristics and asymptotic behavior of dusty-gas motion. In a wide range of conditions a presence of dust in the coma does not affect the gas motion. Therefore, it is possible to study the dynamics of a gas environment separately, without taking into account the dust. The present work is devoted to the gas environment of the comet. The main goal of the work is to develop a simplified model of gas environment which allows to estimate spatial distribution of gas parameters in the coma in the range of nucleus-centric distances from ten to thousand radius of the nucleus.