Orbital Sciences Corp. plans to re-engine its Antares launch vehicle and use one or two alternate launch vehicles initially to meet its International Space Station resupply commitments to NASA after last week’s launch failure with an Antares powered by two Aerojet Rocketdyne AJ-26 engines.

David Thompson, Orbital chairman and CEO, told analysts Wednesday the surplus Russian-built engines have a "fundamental reliability issue" and probably were responsible for the Oct. 28 mishap, which destroyed an Orbital Cygnus cargo vehicle loaded with 4,883 lb. of consumables, hardware and science equipment for the ISS.

However, he declined to specify which engine will replace the AJ-26, repeating an earlier statement that Antares remains in contention for "a number of new launch contracts" that may ride on the engine choice. Russian news outlets have identified the new RD-193, kerosene-fueled engine as Orbital’s pick, and other possibilities include a single Russian RD-180, a solid-fuel rocket motor proposed by ATK, and even restarting production of the Russian NK-33 that is the basis for the AJ-26.

Thompson said Orbital is in discussions with three launch services providers for one or two flights next year with the upgraded Cygnus that was already in preparation for the company’s next mission to the ISS. While he declined to identify those companies, they apparently are SpaceX, United Launch Alliance (ULA) and Arianespace, based on Thompson’s description of them as two U.S. companies and one in Europe.

The SpaceX Falcon 9 already is delivering cargo to the space station in that company’s Dragon cargo carrier. ULA has said it is ready to deliver more Delta II launch vehicles that would approximate the Antares capability. Arianespace markets Russian-built Soyuz rockets flying from the European Space Center in French Guiana and Baikonur Cosmodrome, where Russia’s Progress cargo-carriers are launched on Soyuz vehicles.

Thompson said preliminary evidence from telemetry and debris recovered at the state-owned Antares launch complex on Wallops Island, Virginia, "strongly suggests" that one of the two AJ-26s on the vehicle failed 15 sec. after ignition. The engine had passed a hot-fire acceptance test at Stennis Space Center, where last May another AJ-26 failed when its oxygen turbopump essentially "came apart," in the words of William Gerstenmaier, associate NASA administrator for human exploration and operations.

Initial evidence also points to the turbomachinery as the site of the more recent AJ-26 failure, Thompson said. The ensuing explosion, which was triggered by range safety officers shortly before the fuel-filled vehicle fell back to Earth, caused "relatively limited damage" to the pad, and should be repairable at a "small fraction" of the time and money that went into the pad’s initial construction.

An initial assessment by NASA found the transporter/erector that lifts the Antares into the vertical position was damaged by the blast, as were fuel lines, wiring and the pad’s lightning protection system. Thompson said equipment owned by Orbital is covered by insurance.

"From a financial standpoint, the impacts to Orbital are not expected to be material on an annual basis in 2015, although the exact magnitude and timing of quarterly changes will depend on which of several specific variations on the overall plan we settle on," Thompson said. "And in any event, I do not expect any significant adverse financial impacts in 2016 or in future years."

Thompson credited contingency planning for Orbital’s hoped-for ability to return to flight quickly, and to be able to fulfill its commitment to launch 20,000 kg of cargo to the ISS under its $1.9 billion Commercial Resupply Services contract with NASA by the end of 2016. That will be done with the upgraded Cygnus vehicle, which can carry as much as 3,300 kg of versus the 2,600-2,700 kg of the initial configuration.

With the launch failure, Orbital wants to drop one of the five remaining flights under its CRS contract and make all of its deliveries in four with the larger cargo vehicle. Thompson said his company has started discussions with NASA on that proposal.