Broadcasting radio programs from satellites to mobile users has been operating for many years in the United States, Canada and South Korea. The service, generally called Satellite Radio, is provided at S-band radio frequencies. Satellite Radio users require near perfect service availability. Since most users are mobile (automobiles and handheld reception), the antennas of their receivers have little gain necessitating very high effective isotropic radiated power (EIRP) from the satellite to provide the required availability particularly under fading conditions. Despite using a satellite directive transmitting antenna, the achievement of this high EIRP requires a satellite transmitter radio frequency power output of over 7 kW. This is typically achieved by paralleling 32 Traveling Wave Tube Amplifiers (TWTAs). The configuration, usage and technical aspects of such satellite transmitters are described. These satellite transmitters are critical to Satellite Radio service both for performance and for operating lifetime, typically over 15 years. Because of this importance, detailed lifetime laboratory testing is being done on the TWTAs as reported herein. (C) 2012 Elsevier Ltd. All rights reserved.