This is the J2-X. The liquid-fuel cryogenic rocket engine is the modernized version of the J-2, which NASA used in the late-'60s and early-'70s to thrust humans beyond low Earth orbit. (Click any image below for hi-res.)
Remember the picture of the Pratt Whitney Rocketdyne engines that looked an awful lot like a band of Daleks in disguise? That picture may have done a good job of making space shuttle engines look like a bunch of malevolent cyborgs, but there wasn't really anything in the photo to give you a sense of just how…
NASA says they're "Pratt Whitney Rocketdyne engines" from space shuttles Endeavour and Atlantis... but we think they look an awful lot like incognito Dalek shipping containers.