Large-scale liquid rocket engines with regeneratively cooled nozzles will enable reliable and reduced-cost access to space. The coolant that circulates through the internal channels within the nozzle helps maintain adequate wall temperatures to prevent failure, and is contained under high pressure. It has been a challenge to affordably manufacture the intricate nozzle channels and close-out of these channels. As such, NASA has leveraged cladding and additive manufacturing technology to build the nozzle liner and outer jacket that closes out the channels within, and contains the high-pressure coolant fluid. The new capability reduces the time to fabricate the nozzle and allows for real-time inspection during the build. It has been demonstrated on a series of different alloys, hot-fire testing is nearly complete, and micrograph examination has verified that the bonds are reliable with little deformation to the coolant channels. The technology provides new opportunities to manufacture nozzles and chambers and reduce costs.
The freeform channel close-out technology is a large-scale additive manufacturing deposition process that creates a localized bond at each of the channel lands. This technique builds upon large-scale cladding techniques that have been used for many years in the oil and gas industry, and techniques used in the repair industry for aerospace components. The initial development of this technique used off-axis wire freeform laser deposition without filler material internal to the coolant channels. The wire and laser are traversed circumferentially around the nozzle with most of the laser focus being applied to the previous layer, and partial focus on the channel lands. This prevents overheating and burn-through of the channel lands, and enables a robust bond interface at each channel land. After the initial deposition layer, a traditional cladding process can be used to build up jacket support material or manifold welding offsets.