NASA’s Marshall Space Flight Center posted a video chronicling the evolution of the J-2X rocket, intended to be an upper stage for NASA’s new Space Launch System, from concept through to a successful hot fire test last November. The J-2X is actually the latest evolution of a design that reaches back to the Apollo era. The original J-2 was used on the second (S-II) and third (S-IVB) stages of the mighty Saturn V moon rocket. The J-2X updates the design with new materials and manufacturing techniques, and all new electronics. Even at 50 the J-2 is still an impressive engine.
The J-2 has also served as the basis for later engine designs, such as the linear aerospike engine intended for the cancelled X-33 program. The current J-2X program was initially part of the now-cancelled Project Constellation and was intended to be the upper stage engine for both the Ares I and Ares V. It is one of the components that was carried over into the replacement Space Launch System program when Constellation was cancelled.