WASHINGTON — The explosion of an Orbital Sciences Corp. Antares rocket seconds after liftoff Oct. 28, destroying a Cygnus cargo spacecraft, will likely have a modest near-term effect on NASA and international space station operations, but a far greater one on the future of the Antares itself.

The Antares rocket lifted off from Pad 0A at the Mid-Atlantic Regional Spaceport at Wallops Island, Virginia, at 6:22 pm EDT Oct. 28. No technical problems had been reported during the countdown, and the initial seconds after liftoff appeared to be no different from the previous four Antares missions.

However, within 15 seconds after liftoff, video of the launch showed the plume from the Antares’ first-stage engines suddenly brighten, followed by an explosion at the base of the rocket. The rocket fell back to the ground near the launch pad, triggering an even larger explosion that destroyed the vehicle and Cygnus spacecraft, and damaged the pad.

The cause of the failure was not immediately clear. In a statement issued 48 hours after the accident, Orbital indicated that the problem was with the rocket’s first stage but was not more specific.

“All systems appeared to be performing nominally until approximately T+15 seconds at which point the failure occurred,” Orbital reported in its Oct. 30 statement. “Evidence suggests the failure initiated in the first stage after which the vehicle lost its propulsive capability and fell back to the ground impacting near, but not on, the launch pad.”

The mission, designated Orb-3 by NASA, was the third of eight Commercial Resupply Services (CRS) missions that Orbital Sciences is under contract to perform for the space agency. The Cygnus, named by Orbital the “SS Deke Slayton” after the late astronaut, was carrying 2,290 kilograms of cargo for the station.

NASA officials said that the failure will not have an immediate effect on ISS operations. “We’re in good shape from a consumables and supplies standpoint,” William Gerstenmaier, NASA associate administrator for human exploration and operations, said at an Oct. 28 press conference about three hours after the failure. “There was no cargo that was absolutely critical to us that was lost on this flight. The crew is in no danger.”

ISS Program Manager Michael Suffredini said at that press conference there were four to six months of supplies on the ISS. A Russian Progress spacecraft launched to the station Oct. 29, and a Space Exploration Technologies Corp. Dragon spacecraft is planned for launch no earlier than Dec. 9 to deliver more supplies.

About one-third of the cargo on the Cygnus was food and other consumables. Another third was hardware for the station, none of which Suffredini said was irreplaceable or immediately critical for the station. The rest included 29 small satellites that would have been later deployed from the station, as well as experiments, some of which were developed by students.

Antares’ Future

While the failure was a setback to ISS operations, its effects may be greater on Orbital Sciences and the Antares program. Orbital, seeking to extend its current contract to ferry cargo to the station and to win new business for the launch vehicle, was already planning to replace the rocket’s first stage engine, an effort company executives suggested might be accelerated by this failure.

The AJ-26 engines used in the Antares first stage — refurbished versions of the Soviet-era NK-33 engines — were under scrutiny prior to the launch failure. Although the engines had performed well in the previous four launches, an AJ-26 failed during a test at the NASA Stennis Space Center in Mississippi in May. Another AJ-26 failed in a test there in June 2011, a problem traced back to a fuel leak in the engine.

Neither Orbital nor Aerojet Rocketdyne, which provides the AJ-26 engines for Orbital, had disclosed the cause of the May engine failure. In a Sept. 30 speech at the International Astronautical Congress in Toronto, Orbital Executive Vice President  Frank Culbertson said the investigation into that failure was wrapping up.

“We have come up with probably two potential root causes, both of which we can screen for,” he said at the conference. Engine tests were scheduled to resume in October at Stennis, but Aerojet Rocketdyne spokesman Glenn Mahone said Oct. 29 that the company had been waiting until after the Antares launch to resume those tests.

At the post-failure press conference Oct. 28, Culbertson declined to speculate on any role AJ-26 problems may have played in the launch failure. The engines used on this vehicle had gone through normal acceptance testing both at Stennis and at Wallops prior to the launch. “We didn’t see any anomalies or anything that would indicate there were problems with the engine,” he said.

In a conference call with financial analysts Oct. 29, Orbital executives suggested that the failure may accelerate plans they previously announced to replace the AJ-26. Orbital had planned to use the AJ-26 for the remainder of its CRS missions to the ISS, then likely switch to a new engine. The company currently has no Antares missions on its manifest beyond its remaining CRS flights.

Orbital Chief Executive David W. Thompson said in a quarterly earnings call Oct. 16 that the company had selected a replacement engine, but declined to announce that choice. Speculation about the new Antares engine has ranged from a solid-rocket motor provided by ATK, with whom Orbital is merging, to a derivative of the RD-180 engine from Russian manufacturer NPO Energomash.

“It is possible that we may decide to accelerate this change if the AJ-26 turns out to be implicated in the failure,” Thompson said in the Oct. 29 call. The first launch of an Antares with a “second-generation” engine was about 24 months away prior to this failure, he said, but he did not know by how much Orbital could accelerate the introduction of the new engine.

Thompson said it likely would be “days, not weeks” for Orbital to narrow down the potential causes of the Oct. 28 failure. He expected the next Antares launch, previously scheduled for April 2015, would likely be delayed at least three months. “It certainly could be considerably longer than that, depending on what we find in the review,” he cautioned. “I hope it would be not more than a year.”

As NASA and Orbital investigate the failure, recover the ISS science lost in the accident, and make decisions on the future of the Antares program, they are — for the time being — avoiding major political scrutiny. While NASA’s plans to commercialize ISS cargo and eventually crew transportation have been the subject of controversy in the past, the agency and the company got messages of condolences from Capitol Hill in the failure’s immediate aftermath.

“We add our disappointment to the thousands in the space community who worked tirelessly in support of Tuesday evening’s launch attempt at Wallops Island,” Reps. Lamar Smith (R-Texas) and Steven Palazzo (R-Miss.), the chairmen of the House Science Committee and its space subcommittee, respectively, said in a statement. “We anticipate learning more about the circumstances surrounding the launch failure in the near future.”

“I remain supportive of Spaceport Wallops and NASA’s Commercial Cargo mission in achieving America’s independence in transporting supplies to the Space Station,” Sen. Barbara Mikulski (D-Md.), chairwoman of the Senate Appropriations Committee and a long-time supporter of launch activities at Wallops, said in an Oct. 29 statement.

“Something went wrong and we will find out what that is,” Orbital’s Culbertson said Oct. 28. “We will correct that and we will come back and fly here at Wallops again, hopefully in the very near future.”

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...