NASA has asked commercial partner Orbital ATK to set aside its Antares rocket for the company’s next mission to the International Space Station and instead fly cargo on an Atlas V rocket — the premier vehicle of the United Launch Alliance. The move is aimed at getting more cargo to the ISS in early 2017, since the Atlas V has a greater lift capability than the Antares.

The Antares returned to flight just last month

It’s an ironic decision since the Antares successfully returned to flight just last month. The rocket had been grounded for the past two years, after a previous version of the vehicle exploded in a spectacular fireball during a launch in October 2014. The accident prompted Orbital ATK to do an intense refurbishment of the Antares, and the updated rocket performed a flawless first launch from NASA’s Wallops Flight Facility in Virginia three weeks ago.

The rocket will be sidelined only temporarily, however. Orbital ATK will launch its Cygnus cargo capsule on top of an Atlas V rocket this spring from Cape Canaveral, Florida. The company’s remaining four cargo missions in 2017 and 2018 will be done with the Antares in Virginia. "With five Antares launches from October 2016 through 2018, together with the Atlas V rocket, this plan represents the company’s commitment to establishing schedules that are realistic and achievable," Orbital ATK said in a statement.

The Wall Street Journal reported yesterday that NASA was interested in the Atlas V, and the agency confirmed the switch today to The Verge. "We mutually agreed with Orbital ATK to use an Atlas V for the company's seventh contracted cargo resupply mission to the space station in the spring," NASA told The Verge in a statement.

The pivot was made to fulfill NASA’s need for "enhanced schedule assurance" for its ISS resupply missions, according to Orbital ATK. Orbital can launch 300 kilograms, or 660 pounds, more cargo on the Atlas V than it can with the Antares, according to Frank DeMauro, Orbital ATK’s vice president and general manager of the advanced programs division. "We’re demonstrating our commitment to our customer to be able to lower their risk and get them more cargo, and we’re doing that by going out of house for another rocket," says DeMauro.

It also doesn’t hurt that the Atlas V has a nearly perfect launch record, but DeMauro clarifies that the move was not based on reliability. "This has nothing to do with the Antares’ capability," he says. "We would still be able to support three missions next year."

"We're demonstrating our commitment to our customer."

NASA may want to increase the amount of cargo to the station since its other commercial cargo provider SpaceX is grounded right now, following a launch pad accident on September 1st. SpaceX is aiming to return to flight before the end of the year, but it’s unclear if the company will meet that deadline, and even if it does, the timeframe for its resupply missions for NASA is uncertain.

That means that the space agency is relying on Russia, Japan, and Orbital ATK to periodically supply the station for the time being. A Russian Progress cargo ship and a Japanese HTV cargo ship will bring supplies to the station before the end of the year, but SpaceX’s upcoming resupply mission, originally scheduled for November, is going to be delayed. NASA expects it will need another commercial resupply mission in early 2017, and it wants the added capabilities of the Atlas V for the job.

DeMauro says launch contracts still haven’t been finalized for the Atlas V launch, but it shouldn’t be a difficult transition for Orbital ATK, since the company has launched on the Atlas V before. While the Antares was undergoing refurbishments, Orbital ATK launched its Cygnus cargo capsule twice on the Atlas V, and both launches were a success. "We designed the Cygnus to be compatible with multiple launch vehicles, and we’re using that capability now," says DeMauro.