A range safety officer (RSO) monitors in real time the satellite launch vehicle performance to minimise damage likely to be caused in case of failure and destroys it if it deviates from the mission path and is likely to fall on populated areas. The RSO has to correlate interpretations from tracking and telemetry sources by observing various displays. This paper presents a knowledge-based system, range safety advisor (RSA), which attempts to synthesise interpretations from both tracking and telemetry sources and displays the correlated decision and assists the RSO. It employs knowledge from range safety experts, past flight history, nominal data, etc., to infer the vehicle status and presents a comprehensive icon-based graphic screen with the required information and inferences. Visualization is used effectively to design the output screen to convey a very meaningful picture of the vehicle status along with other important parameters. The RSA system is operational and has been tested in real time during the PSLV-D2 launch.