The framework of the work is an Environmental Monitoring System (EMS) realized by a Satellite based Sensor Network (SSN). The paper introduces and formalizes specific performance metrics needed to implement an efficient Sink selection process (where Sink represents a Satellite channel access node) based on a Multi-Attribute Decision Making algorithm. It is aimed at enhancing the functionality of the whole EMS in terms of reliability, reactivity and spent energy. The reference metrics are packet loss rate, average packet delay, and energy consumption. The algorithm is tested through simulation. KeywordsSatellite Sensor Networks, Sink Selection, Multi Attribute Programming and Performance Evaluation.