Pre-amplifier, amplifier & filters convert the high voltage DC power to RF power having low noise and harmonic content. There are 0.1 to 1.5 million identical devices in one system. This is the highest single contributor to dissipation loss (15 to 19%) with the amplifier contributing 90% of that dissipation. The simplest design concept still results in the most complex mechanical, electrical & thermal set of technology development problems in the system. This combines with requirements for the development of a high production rate at low cost, resulting in reliable operation over a long life. What the noise & harmonic characteristics for the converters are and how they will act in cascade are not known. Filter requirements are to be determined. Ability to develop all the parts, interface them with each other and with the slotted array and operate them with full control and stability constitutes a high development risk and requires the longest lead time in an ambitious development program. Risk rating should then be a very strong 4+++. Most critical and unusual requirements for materials in this application relate to the presence of the exposed cathodes of the rf generators. In addition, it is desirable that structural thermal strain be small so that distortions over the large dimensions are manageable. The waveguide distortions must be small to permit efficient phase front formation. The waveguide deployed configuration results in low packaging density so that it is desirable to form the low density configuration on orbit out of material packaged for high density launch. Before meaningful technology development can begin relating to fabrication, manufacture & assembly, it is necessary to determine the applicability of the non-metallic materials in particular as they relate to potential contamination of the open cathodes of the rf generators. Due to the critical interaction of materials with structures, waveguides and rf generators, the materials development risk rating should be a strong 4++.
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