An Orbital ATK Antares rocket lifts off from Wallops Island, Virginia, Oct. 17, carrying a Cygnus cargo spacecraft bound for the ISS. Credit: NASA/Bill Ingalls

Updated at 10:55 p.m. Eastern.

WASHINGTON — In its first flight in nearly two years, an Orbital ATK Antares successfully launched a Cygnus cargo spacecraft to the International Space Station Oct. 17.

The Antares lifted off from the Mid-Atlantic Regional Spaceport at Wallops Island, Virginia, at 7:45 p.m. Eastern, at the end of a five-minute launch window. The launch shifted from the beginning to the end of the window because of an unspecified but minor engine issue.

Frank Culbertson, president of Orbital ATK’s Space Systems Group, said at a post-launch press conference that the five-minute delay was designed to give controllers enough time to catch up in the final minutes of the countdown. “The launch conductor decided, to make sure we didn’t miss anything in the checklist, to add five minutes,” he said. “It made sure nobody skipped anything.”

The launch itself went as planned, as the RD-181 engines in the first stage and the Castor 30XL motor in the second stage accelerated the Cygnus spacecraft, on a mission designated OA-5, into orbit. The Cygnus separated from the Antares’ upper stage nine minutes after liftoff.

The launch was the first for the Antares since an October 2014 mission that suffered an engine failure seconds after liftoff, causing the vehicle to fall back to the ground and explode. That explosion caused $15 million in damage to the launch site. Orbital ATK decided shortly after that accident to replace the AJ26 engines previously used on the Antares with new RD-181 engines from NPO Energomash.

Culbertson said the upgraded Antares performed better than expected, putting the Cygnus in an orbit slightly higher than expected, but one that poses no issues for the spacecraft’s arrival at the station. “Since it was the first flight of this configuration, we had fairly conservative estimates of what the results would be,” he said. “The first stage was a little bit above what we expected.”

The launch went through a number of delays. Once planned for August, NASA and Orbital ATK postponed the mission eventually to early October because of ISS schedules and additional time needed by the company to resolve issues found during a static-fire test of an Antares first stage at the end of May. Various technical and weather issues, including the passage of a hurricane that shut down a tracking station Bermuda, delayed the launch by several days to Oct. 16. A problem with a ground support equipment cable postponed the Oct. 16 launch.

The Cygnus, named the SS Alan Poindexter after the former astronaut who died in 2012, is carrying 2,425 kilograms of cargo for the ISS. That cargo includes science experiments, crew supplies and station hardware. Joel Montalbano, NASA space station deputy manager, said at an Oct. 15 briefing that NASA replaced ballast on the Cygnus with additional supplies and other cargo because of likely delays in upcoming SpaceX Dragon cargo flights after a Sept. 1 Falcon 9 pad explosion.

Cygnus will arrive at the ISS on Oct. 23. That arrival is later than usual because of the scheduled launch of the Soyuz MS-02 spacecraft, carrying three new station crew members, on Oct. 19. That spacecraft will dock with the ISS Oct. 21. It will depart the station in late November, performing a combustion experiment and deploying several cubesats before reentering.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...