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The #3 TD-339 vernier engine, showing some of the propellant plumbing.

The sphere cut off at left (with the black band) is the high-pressure helium tank. The tank right behind the engine is the fuel tank, and the tank cut off at right is the oxidizer tank.

Vernier #2 was a fixed engine; note the straight-forward arrangement of the propellant supply lines (silver lines above the engine, terminating at the engine's left).