Описан программный комплекс Coulomb, предназначенный для моделирования электризации космических аппаратов (КА) в магнитосферной плазме на высоких и низких околоземных орбитах. Рассмотрены физические механизмы электризации КА и методы математического моделирования этого явления в разных областях космического пространства. Приведены примеры результатов расчета распределения электрического потенциала на поверхности и в окрестности КА для геостационарной орбиты и низких околоземных орбит.

The Coulomb software complex for modeling of spacecraft charging in magnetosphere plasma in high and low Earth orbits is described. Physical mechanisms of spacecraft charging and methods of mathematical modeling of this phenomenon in various areas of space are considered. Examples of the calculation results of electrical potential distribution on the spacecraft surface and in the vicinity of the spacecraft in geosynchronous and the low Earth orbits are presented.

In the paper, we discuss numerical modeling of spacecraft charging in geosynchronous orbit which was done using Coulomb-2, NASCAP-2K and SPIS codes, and present data obtained using the MUSCAT code too. The main distinctive features of the codes above are specified, description of the Coulomb-2 code is given in more details. We compare the results of calculations obtained for similar models of spacecrafts with identical surface materials and parameters of the space plasma environment. The possible reasons of divergence of the modeling results are discussed.

Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.

The results of magnetospheric plasma fluxes measurement in geosynchronous orbit are presented. The measurements were done onboard the geosynchronous Russian "Electro" spacecraft (SC) in 1995-1997 years. The diurnal variations of the plasma density and temperature were observed at various levels of geomagnetic activity.Distortions of the measured electron and proton spectra caused by negative potential of the charged SC were registered. Typical electron spectra and plasma parameters were determined for various SC charging levels. Similar measurements in low polar orbits at the "Meteor" SC (launched in 2003 year) and the "Universitetskiy-Tatyana" SC (launched in 2005 year) were done. (C) 2008 COSPAR. Published by Elsevier Ltd. All rights reserved.

Charging of spacecrafts in near–earth orbits is determined by space environment in the orbit. Dominating physical processes are different in principle for various altitudes. So, the spacecraft charging model which is based on computation of external particle fluxes on the spacecraft surface should include (a) space environment data, (b) adequate description of physical processes of surface/environment interaction including secondary processes, (c) algorithm of the spacecraft surface model construction, and (d) numerical methods for solution of the problem. In this work, we consider items (b) and (c) mainly as the most actual to be solved for simulation of spacecraft charging in various orbits. Our model of spacecraft charging in geosynchronous orbit (GEO) [1–3] was implemented in the COULOMB program package successfully used for modeling of GEO satellites [2, 3]. The principle difference between spacecraft charging in GEO and one in low-earth orbits (LEO) is determined by the fact that plasma of magnetosphere is hot and rare, and one of ionosphere has low temperature and high density. In this case, new method for computation of primary particle fluxes on the spacecraft surface was developed and implemented in the program package NPI_LEO. To do the simulation of spacecraft charging in LEO, we need the procedure of mathematical description of real spacecraft surface. The procedure was developed earlier [3] and employed in the COULOMB package. In the NPI_LEO package, the method developed was generalized to provide a powerful tool for 3D modeling of spacecraft charging in LEO. Physical model of spacecraft charging was built after detailed analysis of principle physical peculiarities of the ionosphere plasma particle currents in the vicinity of spacecraft in LEO. Charging of real spacecrafts was investigated, and the results are presented in Sec. 4 below.

Analysis of measurement data obtained for hot magnetosphere plasma fluxes in geosynchronous orbit has enabled to establish correlation between geosynchronous spacecraft charging and the plasma parameters. The measurements were done onboard the Russian geosynchronous GORIZONT and ELECTRO spacecrafts during years 1992-1993 and 1995-1997 correspondingly. Distortions the measured electron and proton spectra caused by negative spacecraft potential were registered. Spacecraft charging was observed not only in the Earth's shadow (during vernal and autumnal equinoxes), but in the sunlit orbit segments. Well-defined correlation between the spacecraft charging (potential value) and the electron flux parameters ("hardness" of the electron energy spectrum) was revealed. Negative potential values in the 0.2-8.0 kV interval were observed. Typical electron spectra and plasma parameters were determined for various spacecraft charging levels.

Cold plasma ion capture surface construction algorithm was developed in terms of the classical approach to solution of the severely charged body problem (Al'pert et al, 1964). The algorithm makes it possible to create the effective surface for complicated spacecraft outer surface. Peculiarities of the severe charging case modeling, as far as the computation results are presented and discussed.Computations reveal that noticeable distortions of the primary spacecraft surface arise in the case of differential charging corresponding to the spacecraft with dielectric elements on its surface.Effective method for color visualization of the electrostatic potential distribution on the spacecraft surface was developed for analysis of the spacecraft charging modeling. Typical screenshots of VRML images are presented in the work for various charging cases.

The peculiarity of spacecraft charging dynamic processes on GEO is determined by the mechanism of suppression of an secondary electron emission by a retarding electrical field and sharply differing timescales of charging processes, including fast change of external conditions (plasma, sunlight, spacecraft orientation), For numerical simulation of development of spacecraft charging processes in time the automatic multistep Gear method specially intended for the decision of "stiff" systems of the ordinal differential equations is used in this work.The increase of performance modem PC has allowed to use this method for spacecraft models with number of elements more than 1000. The tests show high stability and accuracy of the used methods even at influence of spacecraft model sampling degree. This algorithm is realized in the new version of spacecraft charging tool "Coulomb", constructed as the WWW client - server.The tools includes the interactive builder of spacecraft models and 3D display system of the information and results of accounts, material properties and space plasma parameter databases, tools for solution of electrostatic and dynamic problems, and scenario manager tool.The tool use HTML browsers with VRML by plug-in, WWW Apache server with PHP and mySQL extensions, which allows using it in local and remote access mode. The described technique is applied to the of spacecraft charging analysis on a GEO and HEO under various conditions: in the eclipse and in the sunlight, slow or fast rotation spacecraft in sunlight, movement of a shadow on a surface spacecraft, and also at time variation of plasma parameters. The results of spacecraft charging calculation are presented.

This report presents some examples of a computer simulation of spacecraft interaction with space environment. We analysed a set data on electron and ion fluxes measured in 1991 1994 on geostationary satellite GORIZONT-35. The influence of spacecraft eclipse and device eclipse by solar-cell panel on spacecraft charging was investigated. A simple method was developed for an estimation of spacecraft potentials in LEO. Effects of various particle flux impact and spacecraft orientation are discussed. A computer engineering model for a calculation of space radiation is presented. This model is used as a client/server model with WWW interface, including spacecraft model description and results representation based on the virtual reality markup language.

Введение В НИИЯФ МГУ разработаны физико-математические модели электризации космических аппаратов (КА), функционирующих на геостационарной и низких орбитах [1]. В настоящее время появились новые программные комплексы для математического моделирования физических процессов в реальных трехмерных объектах и методы решения сложных систем нелинейных уравнений большой размерности, которые позволяют провести модернизацию существующих моделей, значительно улучшить их функциональность и расширить область применимости. В настоящей работе рассмотрены основные особенности новой версии математической модели электризации КА и приведены примеры результатов расчетов.