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Overall view into the engine's thrust chamber and nozzle extension.

The thrust chamber itself is the lighter-colored part, while the nozzle extension is a darker grey (almost black). Note the silver ring at the aft end of the thrust chamber; this is the fuel return manifold, where fuel sent down the regenerative cooling tubes comprising the thrust chamber walls turns around and is routed back up to the fuel manifold around the engine's injector.

Also note the gaps between the fuel return manifold and the nozzle extension. Some of the relatively low-temperature gases from the turbine exhaust manifold are vented through these gaps, providing film cooling for the nozzle extension.