Two short reports discuss modifications of a small, lightweight combustion chamber that comprises a carbon/carbon composite outer shell and an iridium/rhenium inner liner. The first report discusses chamber design modifications made as results of hot-fire tests and post-test characterization. The modifications were intended to serve a variety of purposes, including improving fabrication, reducing thermal-expansion mismatch stresses, increasing strength-to-weight ratios of some components, and improving cooling of some components. The second report discusses (1) the origin of stress in the mismatch between the thermal expansions of the Ir/Re liner and a niobium sleeve and flange attached to the carbon/carbon shell and (2) a modification intended to relieve the stress. The modification involves the redesign of an inlet connection to incorporate a compressible seal between the Ir/Re liner and the Nb flange. A nickel alloy was selected as the seal material on the basis of its thermal-expansion properties and its ability to withstand the anticipated stresses, including the greatest stresses caused by the high temperatures to be used in brazing during fabrication.

This work was done by Brian E. Williams and Shawn R. McNeal of Ultramet for Johnson Space Center. For further information, contact the Johnson Innovative Partnerships Office at (281) 483-3809.