The Flash Evaporator System (FES) is part of the Shuttle Orbiter Active Thermal Control Subsystem. The FES provides total heat rejection for the vehicle Freon Coolant Loops during ascent and entry and supplementary heat rejection during orbital mission phases. This paper reviews the performance of the FES during the first two Shuttle orbital missions (STS-1 and STS-2). A comparison of actual mission performance against design requirements is presented. Mission profiles (including Freon inlet temperature and feedwater pressure transients), control temperature, and heat load variations are evaluated. Anomalies that occurred during STS-2 are discussed along with the procedures conducted, both in-flight and post-flight, to isolate the causes. Finally, the causes of the anomalies and resulting corrective action taken for STS-3 and subsequent flights are presented.