The scientific goal of present grant application is to define specific scientific objectives and observing sequences for STIX with special attention focused on in the expected influence of radiation environment on the unusual orbit around the Sun. The objective is to be achieved through further development of the instrument simulation tools, continuation of development of scientific data analysis software and indepth analysis of already collected observations of coronal hard X-rays sources. Important will be study of thresholds for detection by STIX of a polarized component of solar flare emission