The June 9 test-stand fire that ruined one of the two rocket engines scheduled to power the first flight of the Orbital Sciences Corp. Taurus II launch vehicle was caused by kerosene fuel leaking from a 40-year-old manifold manufactured in the former Soviet Union.

Initially the fire was thought to have been triggered by a fuel leak in the test stand at Stennis Space Center, Miss. Subsequent analysis revealed that the leak came from a fuel manifold on the outside of the Soviet-era NK-33 rocket engine, which has been modified by Aerojet and redesignated the AJ-26.

As a result, Aerojet is evaluating all of the three dozen AJ-26s in its inventory to ensure that they are free of corrosion or some other flaw that might have caused the leak on the damaged engine, according to an Orbital spokesman.

“We’re screening the remaining inventory of AJ-26s to double-check to make sure none of the other ones have the problem,” says Barron Beneski, Orbital vice president of public relations. “If they do, we’ll set them aside for some extra inspections.”

The engine lost in the fire was destined for static testing at the new Taurus II launch pad on Wallops Island, Va., and for a first flight now rescheduled from September to mid-December.

Orbital plans to substitute the next engine cleared by the nondestructive evaluation process worked out after the fire. That engine will get a hot-fire test at Stennis and move on to Wallops for integration into the launch vehicle.

“We don’t expect that this is the driving piece in the schedule,” the Orbital spokesman says. “We think we will have engines capable of carrying out the first couple of missions. The long pole in the tent right now has been the construction process for the launch site and the infrastructure.”

Delays that Beneski characterized as routine for large construction projects have slowed work on the Taurus II pad at the Mid Atlantic Regional Spaceport, a Virginia state facility on NASA’s Wallops Flight Facility. The latest plan calls for construction and certification of pad facilities to be completed in time for a static hot-fire test there late in September or early October. Launch of an initial risk-reduction flight, which will be carried out with extra funds in the fiscal 2011 spending plan Congress approved for NASA, would follow in mid-December.

That would set up a combined rendezvous, proximity operations and berthing test flight for the Taurus II and its Cygnus cargo capsule in mid-February, which Orbital must accomplish to get paid under NASA’s Commercial Orbital Transportation Services (COTS) seed-money effort to spur private investment in International Space Station resupply vehicles. Beyond that, Orbital Sciences believes it has enough engines on hand to fly out the eight flights covered in its $1.9 billion follow-on station-resupply contract.

“Our expectation is that we’re probably likely to see a few engines that we’re going to want to set aside for some additional inspection,” the Orbital spokesman says. “How many that is, what the breakout is, we don’t know, but our expectation is we’re going to have plenty of engines to fulfill our upcoming schedule.”

Beneski stresses that Aerojet, Orbital’s subcontractor on the Taurus II development, has the lead on resolving the AJ-26 issue. “We’re very much on top of the issue and Aerojet to get it right,” he says.

Aerojet did not immediately return calls regarding the issue.