Orbital Sciences Corp. and Aerojet said Feb. 24 that a so-called pathfinder version of the AJ-26 engine chosen for Orbital’s Taurus 2 medium-lift rocket had arrived at NASA’s Stennis Space Center in Mississippi for testing.

The pathfinder engine will be used to verify test stand interfaces, engine handling processes and test configurations prior to the start of three months of hot fire tests slated to begin in April, Orbital and Aerojet said in a joint press release.

The AJ-26 is a liquid oxygen-and-kerosene-fueled main-stage engine based on the Russian-built NK-33 engine. Aerojet has been developing design modifications for the engine since 1993 to make it suitable for commercial launchers. RocketplaneKistlerbaselined the AJ-26 for the K-1 reusable launch vehicle it was developing with financial assistance from NASA’s Commercial Orbital Transportation Services (COTS) program until its $207 million agreement was terminated in 2007 after repeatedly failing to obtain private financing. Kistler’s failure opened the way for Orbital to win a $178 million COTS contract to build and demonstrate Taurus 2 and its Cygnus cargo-carrying vehicle on a flight to the international space station now slated for March 2011.