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The debut launch of an upgraded version of Orbital ATK’s Antares rocket has slipped to Friday after ground teams resolved a minor vehicle issue and made emergency preparations for Hurricane Matthew, which bypassed the Antares launch site on Virginia’s Eastern Shore this weekend.

The two-stage booster, powered by new RD-181 engines from Russia, is set for blastoff from pad 0A at the Mid-Atlantic Regional Spaceport at 8:51 p.m. EDT Friday (0051 GMT Saturday), Orbital ATK said in an update Monday.

The launch was expected Thursday evening, but Orbital ATK said workers ran behind in preparations this weekend as technicians prepared to connect the Antares rocket with its payload, a Cygnus supply ship ferrying around 5,000 pounds of cargo to the International Space Station.

With the one-day slip, the Cygnus spaceship should reach the space station early Monday, instead of Sunday.

“The Antares and Cygnus team encountered and resolved a minor vehicle processing issue over the weekend which, together with time spent on contingency planning for Hurricane Matthew, necessitated the one-day slip,” the statement said. “This updated schedule is still subject to the completion of all remaining pre-launch testing and operational activities, as well as acceptable weather conditions prior to and during launch operations.”

The rocket is now set to roll out from its integration hangar at Wallops Island, Virginia, on Wednesday. The 133-foot-tall (40-meter) launcher will be lifted vertical on top of its launch mount after a one-mile journey from the Antares assembly building.

Forecasters were worried Hurricane Matthew would continue northeast up the U.S. East Coast after slamming Florida last week, but the storm dissipated and turned out to sea.

Ground crews finished loading all the cargo into the Cygnus spacecraft last week, and the schedule called for the supply freighter to be attached to the Antares rocket Sunday, followed by its encapsulation inside the Antares payload fairing.

The upcoming flight will mark the maiden launch of the Antares 230 vehicle, a configuration that eliminates the use of AJ26 first stage engines, which Orbital ATK blamed for a fiery crash during the last Antares flight in October 2014.

Orbital ATK ordered newly-manufactured RD-181 engines from Russia’s NPO Energomash, a rocket engine supplier for United Launch Alliance’s Atlas 5 booster, to replace the AJ26 engines on the Antares first stage.

The AJ26 engines were built in the 1970s for the Soviet Union’s N1 moon rocket. Once the Russian moon landing program was canceled, officials put the engines into storage until Aerojet Rocketdyne imported the powerplants to the United States in the 1990s, modified the engines to fly on U.S. rockets, then sold them to Orbital ATK — then known as Orbital Sciences — for the Antares launcher.

But the engines proved troublesome, with a failure on a ground test stand in May 2014 before causing the Antares rocket crash five months later.

Orbital ATK intended to move away from the AJ26 engine before the 2014 launch failure, but the accident accelerated the company’s plans.

The RD-181 engine produces about the same level of thrust as the AJ26, burns the same mixture of RP-1 kerosene and liquid oxygen propellants, and is about the same size as the Antares rocket’s previous propulsion system.

Besides the improvement in reliability expected by Orbital ATK, the RD-181 engines produce about 13 percent more thrust than the AJ26s, and they are more efficient.

“The combination of those two (improvements) give us a good 20 to 25 percent performance improvement to the orbit that we’re flying to in low Earth orbit to inject the Cygnus for these cargo runs,” said Kurt Eberly, Orbital ATK’s deputy Antares program manager, in an interview with Spaceflight Now earlier this year.

The single-chamber RD-181 is similar to the dual-nozzle RD-180 engine flown on United Launch Alliance’s Atlas 5, producing about the thrust of its larger cousin. NPO Energomash produces a nearly identical engine named the RD-191 for Russia’s Angara rocket family.

Eberly said the new engines required a new type of thrust adapter, a structural component that mechanically connects the RD-181s to the first stage. Orbital ATK also built avionics systems for the engines, developing the new controllers in-house to replace the AJ26 controller sourced from an external supplier.

Orbital ATK has a multibillion-dollar contract with NASA to dispatch equipment, experiments and provisions to the space station. Friday’s launch will start the sixth of at least 17 resupply missions under contract to Orbital ATK.

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