Low-Cost, High-Performance Combustion Chamber

Ultramet designed and fabricated a lightweight, high-temperature combustion chamber for use with cryogenic LOX/CH4 propellants that can deliver a specific impulse of approx.355 seconds. This increase over the current 320-second baseline of nitrogen tetroxide/monomethylhydrazine (NTO/MMH) will result in a propellant mass decrease of 55 lb for a typical lunar mission. The material system was based on Ultramet's proven oxide-iridium/rhenium architecture, which has been hot-fire tested with stoichiometric oxygen/hydrogen for hours. Instead of rhenium, however, the structural material was a niobium or tantalum alloy that has excellent yield strength at both ambient and elevated temperatures. Phase I demonstrated alloys with yield strength-to-weight ratios more than three times that of rhenium, which will significantly reduce chamber weight. The starting materials were also two orders of magnitude less expensive than rhenium and were less expensive than the C103 niobium alloy commonly used in low-performance engines. Phase II focused on the design, fabrication, and hot-fire testing of a 12-lbf thrust class chamber with LOX/CH4, and a 100-lbf chamber for LOX/CH4. A 5-lbf chamber for NTO/MMH also was designed and fabricated.