At present day, it is easily noticeable how the interest for environmental impact of human activities is becoming more and more important. Space utilization is not exempt from this, thus new ways of estimating pollutant and greenhouse gases emissions of launchers are needed, especially in a conceptual design phase, during which the consequences of different design choices must be compared. Meanwhile, many new propulsion concepts are currently under design and, in particular, one promising category is that of precooled air-breathing rocket engines, represented by SABRE, from Reaction Engines Limited. This work aims at anticipating propulsive performance and emission estimations of such systems at conceptual design level.