WASHINGTON — Orbital Sciences Corp., which is preparing to send its Cygnus cargo freighter to the international space station (ISS) for the first time later this month, was put on notice Sept. 4 by a NASA official who said the Dulles, Va., company could be needed for another cargo run as soon as December because Space Exploration Technologies Corp. (SpaceX) — the agency’s other cargo-delivery contractor — likely will not be ready to fly.

Orbital is slated to launch Cygnus Sept. 17 from the Mid-Atlantic Regional Spaceport at NASA’s Wallops Island Flight Facility in Wallops Island, Va. It will be Cygnus’ maiden flight and the sophomore effort for its Antares carrier rocket, which flew successfully in its own demo mission April 21. Orbital is slated to carry nonessential cargo to ISS in order to prove the company is ready to begin service under the eight-flight, $1.9 billion Commercial Resupply Services contract it signed with NASA in 2008.

SpaceX also got a delivery contract from NASA in 2008: a 12-flight deal worth $1.8 billion. The Hawthorne, Calif., company already has made two of those runs, the second of which wrapped up in March. Since then, SpaceX has been working on a more powerful variant of the Falcon 9 rocket that launched those missions, as well as an enhanced version of its Dragon space capsule.

That work will keep SpaceX from returning to ISS in 2013, said Michael Suffredini, NASA’s ISS program manager at the Johnson Space Center in Houston. “I would not expect them to be ready in December, or even January time frame,” Suffredini said during a Sept. 4 press briefing from Johnson.

SpaceX spokeswoman Christina Ra, reached by email Sept. 4, had no immediate comment.

Par for the course during the development of a new launch vehicle, SpaceX ran into delays with its so-called Falcon 9 1.1, which is slated to debut Sept. 14 from the Vandenberg Air Force Base in California. The rocket will not carry Dragon on that launch, but a Canadian space weather satellite called Cassiope and several ride-along payloads.

Should Orbital be called upon to make its first contracted cargo run in December, it could mean turning around its launch pad, rocket and spacecraft in just under three months. Back in 2012, SpaceX flew its first contracted cargo run about four months after successfully completing the same type of demonstration mission Orbital will attempt Sept. 17 from the Virginia coast.

In April, Mike Laidley, Orbital’s program director for Antares, said the minimum turnaround time between Antares missions is about one month.

Even if both SpaceX and Orbital should be unavailable in December, Suffredini said ISS is well provisioned and could ride out a missed delivery.

The Ukrainian-built core-stage of each Antares rocket uses two AJ-26 engines, Soviet-vintage, kerosene-fueled engines from a failed Russian Moon exploration program that have been upgraded, refurbished and rebadged by Aerojet Rocketdyne of Sacramento, Calif. Antares’ upper stage is powered by a solid motor provided by ATK Aerospace of Magna, Utah. Cygnus, which is assembled by Orbital at its Dulles campus, is built around a pressurized module provided by Italy’s Thales Alenia Space.

Frank Culbertson, the former NASA astronaut who now runs Orbital’s Advanced Programs Group, said the company already has all the hardware it needs to put together an Antares-Cygnus stack for a December cargo run. Most of that is standing by at Wallops, with the exception of the Cygnus power module that would be used for that flight, and Antares’ solid-fueled second stage.

All told, and excluding the stack to be launched Sept. 17, Orbital has in the United States three rockets worth of hardware standing by, and three Cygnus power modules in varying stages of assembly, Culbertson said. Thales Alenia is now working on the eighth Cygnus pressurized cargo module and has others in storage in Italy awaiting shipment. There is one pressurized cargo module standing by at Wallops, Culbertson said.

Meanwhile, Suffredini took time on the Sept. 4 conference call to highlight NASA’s expectation that both of its cargo-delivery contractors establish reliable service in the near future. “It’s time for us really to start having flights on a regular basis,” he said. “I’m looking for this next year, 2014, to be the year when we fully settle in, where we have regular Orbital flights and regular SpaceX flights and we actually see them, give or take, within a few weeks of when we expect to have them.”

SpaceX and Orbital are under contract for cargo runs through 2016. NASA is expected to seek bids for a second round of commercial cargo delivery service late this year or early in 2014.