TWTA versus SSPA: Analysis Update of the Boeing fleet on-orbit reliability data

There has been longstanding debate regarding the comparative reliability of SSPAs versus TWTAs for the satellite downlink. High voltages, thermionic, life limited emitters operating in a high vacuum enclosure 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 that compare SSPAs and TWTAs rely on transistor device life test data on the ground for SSPAs due to 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. This paper hopes to provide some insight into the failure rates of both amplifiers, thereby clarifying the merits and drawbacks of each design based on orbital performance.