Rocketdyne XRS-2200

The Rocketdyne XRS-2200 was an experimental linear aerospike engine developed in the mid-1990s for the Lockheed Martin X-33 program. The XRS-2200 engine's powerpack was derived from the Rocketdyne J-2 engine, the upper stage engine of the Saturn V moon rocket developed under the Apollo Program in the 1960's. The XRS-2200 used the J-2's combustion cycle and propellant choice.
Rocketdyne intended to develop the subscale XRS-2200 into the RS-2200 for use on the VentureStar. While the X-33 program was cancelled, two XRS-2200 engines were produced and tested.