WASHINGTON — As Orbital ATK prepares to launch a Cygnus cargo spacecraft on an Atlas 5, the company expects to hear soon from NASA about potentially using that rocket again on future cargo missions.

The Atlas 5 carrying the Cygnus spacecraft on a mission designated OA-7 is scheduled to lift off from Cape Canaveral, Florida, at 11:11 a.m. Eastern April 18. Forecasts project a 90 percent chance of acceptable weather for the launch.

The Cygnus, flying the seventh mission under Orbital ATK’s Commercial Resupply Services (CRS) contract with NASA, is carrying more than 3,450 kilograms of cargo to the International Space Station. That cargo includes crew supplies, vehicle hardware, scientific experiments and 38 cubesats that will be later deployed from the station or from the Cygnus spacecraft itself.

Orbital’s original plans called for launching all of its Cygnus spacecraft using the company’s own Antares launch vehicle. However, after an October 2014 launch failure involving a Cygnus, the company purchased two Atlas 5 launches from United Launch Alliance to continue delivering supplies while it redesigned the Antares, replacing the first stage engines at fault in the failure.

The re-engined Antares returned to flight in October, delivering a Cygnus to the ISS, but in November Orbital ATK announced that it would launch the next Cygnus on an Atlas 5. At the time, the company said that it chose the Atlas 5 because of the additional payload performance that vehicle offers, meeting NASA’s desire to deliver more cargo to the station.

“Because there was a slightly increased demand for cargo to the station sooner rather than later, and Atlas had a vehicle available and additional upmass available, we talked to NASA and decided jointly to go ahead with the Atlas,” said Frank Culbertson, president of Orbital ATK’s Space Systems Group, at a NASA press conference April 17 at the Kennedy Space Center.

Orbital ATK plans to return to its own Antares vehicle for the remaining missions under its current CRS contract. The next such launch, Culbertson said, could take place as soon as this summer depending on space station schedules and cargo requirements, he said. The rest are expected to take place through 2018 or early 2019.

Orbital ATK is one of three companies that received follow-on CRS-2 cargo contracts from NASA in early 2016 to deliver cargo to the ISS into the 2020s. Orbital’s contract includes options for Cygnus launches on either the Antares or Atlas 5.

Culbertson said that the company expects to hear from NASA in the near future about the mix of launch vehicles it wants for those missions. “On CRS-2, NASA hasn’t actually told us exactly which missions they’ll want on which vehicles,” he said. “We’re waiting to see which way they’d like for us to go, whether it’s a mix or all one or the other. We hope to hear that pretty soon.”

Joel Montalbano, deputy manager of the ISS program at NASA, didn’t state when NASA would make a decision on the choice of vehicles for those CRS-2 missions, but did note that the agency liked having access to a range of vehicles. “Having the opportunity to launch on different vehicles keeps our program robust,” he said.

Another CRS-2 contract awardee, Sierra Nevada Corporation, also plans to use the Atlas 5 for launching its Dream Chaser cargo spacecraft. The third CRS-2 company, SpaceX, will continue launching its Dragon spacecraft on its own Falcon 9 rockets, as it does today under its current CRS contract.

This particular Atlas 5 launch was delayed by about a month because of technical issues with the rocket and ground equipment. Vern Thorp, program manager for commercial missions at ULA, said at the briefing that separate, unrelated hydraulic problems with ground support equipment and an engine component required repairs that postponed the launch from mid-March.

“Replacing those components didn’t take a lot of time,” he said. “The harder part is doing a very, very thorough anomaly investigation to make sure that you understand what happened to those components, why did they fail and is there anything we need to do to make sure it won’t happen again.”