Orbital Sciences Corp. will launch its next cargo delivery mission to the international space station no earlier than June 17 as the company and its main propulsion supplier investigate why an engine for a future Antares rocket, which does the lifting for the Dulles, Virginia-based company’s resupply missions, failed on the test stand.

Orbital announced the delay in a May 28 post on its website. 

The engine that failed its May 22 acceptance test at NASA’S Stennis Space Center in Mississippi was an AJ-26, a Soviet-vintage product refurbished by Aerojet Rocketdyne of Sacramento, California. The failed engine is not one of the two that will power Orbital’s second contract cargo run to the station, which had previously been scheduled for June 10.

Each two-stage Antares rocket uses a pair of AJ-26 engines in its core stage. Orbital has had issues with this engine before, including a 2011 test stand failure that caused a fire. The company has cited internal corrosion as the probable culprit for the 2011 failure. The engines, originally known as NK-33s and built for a failed Soviet Moon program, were in storage for decades before Aerojet bought them. 

Orbital has access to enough of the engines to finish its eight-flight, $1.9 billion resupply services contract with NASA. Signed in 2008, the deal runs through 2015. Orbital’s Antares rocket launches from the Mid-Atlantic Regional Spaceport at NASA’s Wallops Flight Facility in Wallops Island, Virginia.