WASHINGTON — Orbital Sciences Corp. will buy at least one Atlas 5 rocket from United Launch Alliance to resume cargo deliveries to the international space station for NASA in the fourth quarter of 2015 while it works to return its Antares rocket to flight after an October failure, Orbital said in a Dec. 9 press release.

Dulles, Virginia-based Orbital has contracted for one Atlas 5 launch of its Cygnus space capsule next year, with an option for a second Atlas 5 launch for 2016 “if needed,” the press release said. The missions would launch from Cape Canaveral Air Force Station, Florida.

In what was to be its third paid cargo delivery to the space station for NASA, Orbital’s Antares rocket exploded Oct. 28 moments after liftoff from its launch pad at the Virginia-operated Mid Atlantic Regional Spaceport at NASA’s Wallops Flight Facility in Wallops Island, Virginia.

Orbital is on the hook to deliver 20,000 kilograms of cargo to the station by 2017 under a $1.9 billion Commercial Resupply Services contract signed in 2008. Originally the company planned eight flights, but now says it only needs seven because of the Atlas 5’s extra lifting power and the impending introduction of a larger Cygnus capsule.

Meanwhile, Orbital said it finalized a deal with an unidentified supplier to replace the Antares first-stage AJ-26 engine, a Soviet-vintage product, refurbished and resold by Aerojet Rocketdyne, that Orbital has blamed for the failure. Each Antares uses two AJ-26 engines.

“The first new propulsion systems are expected to arrive at the Antares final assembly facility at Wallops Island, Virginia in mid-2015 to begin vehicle integration and testing,” Orbital said, without identifying the engine or its manufacturer.

Repairs to Orbital’s Virginia launch facility will be completed by the end of 2015, the company said. The upgraded Antares, with its new main stage engine, will begin launching in 2016, with flights now scheduled for the first, second and fourth quarters of that year, Orbital said.