COLORADO SPRINGS, Colo. — An AJ-26 engine slated to power Orbital Sciences Corp.’s Antares rocket on a 2015 mission to the international space station failed May 22 during a hot-fire test at NASA’s Stennis Space Center in Mississippi. 

Orbital Sciences spokesman Barry Beneski confirmed the failure late May 22.

“Yes, there was an AJ26 engine test anomaly earlier today at Stennis. The cause is unknown at this point,” Beneski said in an email. “Engineering teams will gather and examine the data to determine the cause. It was an engine slated for a flight in 2015.”

The AJ-26 is a liquid oxygen- and kerosene-fueled engine originally built for Russia’s abandoned lunar program. Aerojet Rocketdyne of Sacramento, California, has a stockpile of the 1970s-vintage engines that it is refurbishing for Orbital. 

Two AJ-26 engines are used to power the Antares rocket’s main stage. 

Mike Gruss covers military space issues, including the U.S. Air Force and Missile Defense Agency, for SpaceNews. He is a graduate of Miami University in Oxford, Ohio.