State-of-the-art fabrication processes for iridium/rhenium thrust chambers

Chemical vapor deposition (CVD) has been used to fabricate rhenium liquid rocket combustion chambers since 1979. CVD iridium was first applied to rhenium chambers for high temperature oxidation protection in 1986. Since that time, CVD iridium/rhenium (Ir/Re) chambers have been successfully hot-fire tested at various facilities in both nitrogen tetroxide/monomethyl hydrazine (NTO/MMH) and oxygen/hydrogen (O-2/H-2) bipropellants, the latter at mixture ratios ranging from 4 to 17, for a total of nearly 200 hours. An alternate processing method is to form the rhenium by powder metallurgy (PM) and apply the iridium by electrodeposition (ED). To date, hot-fire testing of chambers produced by this ED/PM method includes 43 seconds in NTO/MMH and approximately 11 hours in O-2/H-2 at mixture ratios of 3 to 4, an oxidizing potential that may actually be benign to unprotected rhenium. This paper discusses alternate processing methods and their relationship to fabricating CVD Ir/Re combustion chambers, as well as test methods for evaluating their efficacy.