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 The sources said the preliminary findings suggest that a simple
assembly mistake by Orbital ATK could have caused the explosion,
which destroyed a cargo ship bound for the International Space
Station.
Orbital initially linked the explosion to a problem with the turbo
pump in one of the two Soviet-era NK-33 engines that power the
rocket. GenCorp Inc's Aerojet Rocketdyne unit refurbishes the old
motors and resells them as AJ-26 motors.
Orbital ATK on Friday acknowledged that so-called "foreign object
debris" was one of more than a half dozen credible causes of the
explosion, but said it was not "a leading candidate as the most
probable cause of the failure."
Orbital spokesman Barry Beneski said the company-led "accident
investigation board," which includes officials from NASA and the
Federal Aviation Administration, had not identified any evidence of
mishandling of the flight hardware by Orbital.
He said Orbital continued to compare data from the October explosion
with a May 2014 test stand failure of a different AJ-26 engine, and
prior failures involving AJ-26 ground tests in 2009, 2011 and 2012.
No details have been released on the May 2014 test stand incident,
but sources familiar with the earlier investigation said it was
likely linked to faulty "workmanship" on the original motor, and
additional inspections had been mandated to prevent mishaps with
other engines. Orbital also successfully launched one Antares rocket
in July 2014, after the May incident.
NASA spokeswoman Stephanie Schierholz said NASA was conducting its
own internal "lessons learned" review of the accident, but declined
to give any details about individual aspects of the investigation.
She agreed with Orbital that foreign object debris was always
considered as a possible cause in aerospace accidents.
If the investigations confirm that debris from the fuel tanks caused
the Antares explosion, that could have significant financial and
legal effects for Orbital ATK, which was formed by the merger of
Orbital Sciences Corp and Alliant Techsystems.
The new findings could also open the door for a legal claim against
Orbital by GenCorp, which took a $17.5 million loss in October,
after Orbital said the accident had prompted it to accelerate plans
to switch to a different engine.
One source said the Orbital investigation could end without
declaring a single "root cause" for the explosion. Probes of past
accidents have had similar results.
Several sources said it may be difficult to determine conclusively
whether the debris entered the engine before the explosion, or as a
result of it.
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Glenn Mahone, spokesman for Aerojet Rocketdyne, declined to comment
on the investigations, noting that they were still underway. He also
declined to comment on the cause of the May test stand failure,
which is part of the investigation.
One of the sources familiar with the probe said investigators found
particles of a crystallized desiccant, or drying agent, in the turbo
pump and other parts of the AJ-26 engine. The crystals could have
caused sparks and triggered a fire when they hit the turbo pump in
the oxygen-rich environment, the source said.
Desiccants are often used to control moisture in fuel tanks but need
to be removed before takeoff, the sources said.
While the NASA investigation had not finalized the root cause of the
accident, there were multiple signs that suggested some "foreign
object debris" had been ingested into the engine from the fuel
tanks, one source said.
Antares had four previous successful flights. The Oct. 28 explosion
was the first accident since NASA began using commercial providers
to fly cargo to the space station.
Orbital already faces steep bills for damage to the launch site, and
the need to buy a different rocket to launch its next cargo ship to
the space station.
In December, the company said it would buy a booster from United
Launch Alliance, a joint venture of Lockheed Martin Corp and Boeing
Co, to meet its obligations under a $1.9 billion cargo supply
contract with NASA.
Orbital is one of two companies NASA hired to fly 40,000 pounds of
cargo each to the station following the retirement of the space
shuttles in 2011. Privately held Space Exploration Technologies, or
SpaceX, has the other contract, valued at $1.6 billion.
(Reporting by Andrea Shalal; Editing by David Gregorio)
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