Orbital Sciences pinpointed engines designed by the Soviet Union in the 1960s as the cause of the Antares rocket explosion in Virginia last week, and likely will discontinue using the designs.

The unmanned Antares rocket exploded shortly after liftoff Oct. 28 from NASA’s Wallops Flight Facility. The rocket had been carrying the Cygnus spacecraft that was to deliver supplies and experiments to the International Space Station. Orbital Sciences, the company that holds a $1.9 billion contract with NASA to send supplies to the ISS, said in a statement, “preliminary evidence and analysis conducted to date points to a probable turbopump-related failure in one of the two Aerojet Rocketdyne AJ26 stage one main engines. As a result, the use of these engines for the Antares vehicle likely will be discontinued.”

The engines in question are modeled after Russian designs from the 1960s. Orbital Sciences will be developing new engine models to continue its contracted missions to the International Space Station. Orbital Sciences has five remaining resupply missions under their current contract with NASA.

“Orbital is taking decisive action to fulfill our commitments to NASA in support of safe and productive operations of the Space Station,” said Orbital’s Chairman and Chief Executive Officer David Thompson. “While last week’s Antares failure was very disappointing to all of us, the company is already implementing a contingency plan to overcome this setback.”

The next launch is scheduled for 2016.