WASHINGTON — The recent failure of an AJ-26 rocket engine during ground testing has now delayed Orbital Sciences Corp.’s second contracted cargo run to the international space station until at least July 1, about a one-month slip compared with the original launch date. 

The engine, which failed during a hot fire test at NASA’s Stennis Space Center in Mississippi May 18, is not one of the two that will power the Antares rocket in the upcoming flight. But Orbital nonetheless must determine whether the cause of the failure was isolated to that particular engine.

The Soviet-vintage engine, upgraded and refurbished by Aerojet Rocetdyne of Sacramento, California, was intended for a 2015 Antares launch. Neither Orbital nor Aerojet have said what went wrong during the test, and depending on how long it takes the companies to figure that out, Antares’ second contracted launch could slip even further.

“Once the investigation team reaches the point in their process that they can clear Antares to launch the Orb-2 mission, a targeted launch date will be established,” Orbital wrote in a June 9 press release. “For now, [no earlier than] July 1 is simply a planning date.”

Dulles, Virginia-based Orbital and Aerojet have run into problems before with the engine, originally known as the NK-33 and built in the 1970s for the Soviet Union’s aborted lunar exploration program. In 2012, an AJ-26 caught fire at Stennis’ E-1 test stand. The malfunction, later blamed on a ruptured fuel line, raised questions about the long-term viability of the AJ-26, which was never intended to be stored on the ground for decades before being used.

Despite the hiccups with the AJ-26, Orbital has successfully launched Antares three times from the Mid-Atlantic Regional Spaceport at NASA’s Wallops Flight Facility on Wallops Island, Virginia. 

Each two-stage Antares rocket uses two AJ-26 engines in its core stage.

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Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...