WASHINGTON — The debut of Orbital Sciences Corp.’s Antares Cygnus spacecraft will slip at least to August and possibly to September as the Dulles, Va., company replaces an engine on the freighter’s Antares carrier rocket.

In a May 6 press release, Orbital said its engineers need “to further inspect and confirm the flightworthiness” of this engine. The company did not say what had prompted it to remove the engine in the first place, and Orbital spokesman Barron Beneski could not immediately be reached for comment.

Each Antares core stage uses two liquid-fueled engines: Soviet-vintage NK-33s refurbished and modified by Aerojet of Sacramento, Calif., and remarketed as AJ-26s. Swapping out the engine will take three to four weeks, Orbital estimates. That would push the first Cygnus launch into early August, when Japan’s H-2 Transfer Vehicle is scheduled to lift off on its own cargo mission to the space station. Unless the Japanese mission is delayed, Cygnus would have to wait until September to visit the space station for the first time, Orbital said.

The inaugural Cygnus mission, which had been scheduled for June or July, is the second of two demonstration flights Orbital must perform for NASA before it can begin regular cargo service to the international space station under an eight-flight, $1.9 billion contract signed in 2008. Orbital has already collected on this contract, but the full award is contingent on successful cargo deliveries.

Orbital’s first demonstration flight of Antares happened April 21. Data from that launch show that Cygnus is in store for a smooth ride; first- and second-stage firings all occurred as designed, Orbital said in its press release, as did fairing separation.

“Having intensively reviewed the data for a couple weeks, our conclusion is that the inaugural Antares flight really was as good as it looked,” Mike Pinkston, Orbital’s Antares program manager, said in the press release.

Antares launches from Pad-0A at the Mid-Atlantic Regional Spaceport in Wallops Island, Va. The state of Virginia operates the launch facility, which is part of NASA’s Wallops Island Flight Facility. Orbital has several AJ-26 engines cached nearby the pad in its horizontal integration facility. Likewise, the first Cygnus to fly in space has been loaded with cargo, sealed and fueled and is standing by to be mated with its launcher.


Cygnus on Deck after Successful Antares Debut

Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...