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

The communications industry has depended on TWTAs and SSPAs (solid state power amplifiers) for the long years of service required of the satellite. There has been a longstanding debate regarding the comparative reliability of SSPAs versus TWTAs. High voltages and thermionic life limited emitters contribute to the TWTA risks and reliability questions. The SSPA is an inherently reliable, solid state device requiring only low voltages to amplify, with failure resulting in only graceful degradation. Data from the largest body of on-orbit statistics in the industry are detailed in this paper, examining the on-orbit TWTA and SSPA failure data from BSS satellites. The conclusion is drawn that in terms of watt per rate of failure, the TWTAs provided an order of magnitude more performance than their solid state competition.