TWTA versus SSPA: a comparison of on-orbit reliability data

There has been long-standing debate regarding the comparative reliability of solid-state power amplifiers (SSPAs) versus traveling wave tube amplifiers (TWTAs) for the satellite downlink. High-voltage, thermionic, life-limited emitters operating in a high vacuum enclosure (i.e., a vacuum electronic device) contribute to the TWTA risks and reliability questions. Conventional wisdom espouses the SSPA as an inherently more reliable, solid-state device requiring only low voltages to amplify, with failure resulting in only graceful degradation. However, many trade studies on comparing SSPAs and TWTAs rely on transistor device life test data on the ground for SSPAs due to the lack of statistically significant data on orbit. It is expected that current, on-orbit statistics in the industry would shed relevant light on the debate.