Technicians plan to inspect two AJ26 rocket engines mounted on the next Orbital Sciences Corp. Antares launcher this week to ensure the Russian-built engines are not stricken with the same fault that resulted in a dramatic mishap during a ground test last month, officials said Monday.

Photo of the first Antares launch in April 2013. Photo credit: NASA/Wallops Range Optics
 
Orbital Sciences announced Monday it is targeting liftoff of the Antares rocket on company's next commercial logistics flight to the International Space Station no earlier than July 10.

Orbital's second operational cargo delivery to the space station was supposed to take off June 10, but a May 22 ground test of an AJ26 engine planned to fly on a future launch failed, ending 30 seconds into a planned 54-second "acceptance firing" on a test stand at NASA's Stennis Space Center in southern Mississippi.

The anomaly caused extensive damage to the engine, prompting an investigation by Orbital and its suppliers, led by Aerojet Rocketdyne, the engine's U.S. contractor.

The upcoming resupply mission is designated Orb-2, the second of eight flights in a $1.9 billion deal with NASA.

"The new launch schedule reflects progress in the investigation into the cause of an AJ26 engine test failure and identification of specific actions to clear the Orb-2 mission for flight," Orbital said Monday in a status update posted on the company's website.

Officials have not released any information on the cause of the ground test anomaly.

"The Antares team will inspect the AJ26 engines installed on the Orb-2 rocket this week, and a decision to proceed toward launch will be based on the results of the inspections," officials wrote in the status report.

The engine that failed May 22 was slated to fly on an Antares mission in 2015. The two kerosene-fueled AJ26-62 engines for the next Antares launch passed acceptance testing and are already attached to the Antares rocket inside Orbital's horizontal integration facility near the launch pad at NASA's Wallops Flight Facility on Virginia's Eastern Shore.

Before clearing the rocket for flight, officials want to verify the engines on the next flight are not susceptible to whatever caused the failure on the test stand in Mississippi.

All other elements for the mission are ready to go, according to Orbital. The flight was supposed to launch in early May, but NASA requested Orbital reschedule the flight for June to accommodate delays in launching a SpaceX cargo mission in April.

Orbital's Cygnus and SpaceX's Dragon supply ships use the same attachment port on the space station, and only one vehicle can visit the complex at a time.

The Cygnus spacecraft for the Orb-2 mission is fueled and packed with supplies for the space station and its six-person crew. Workers still need to load time-sensitive cargo a few days before launch.

The Cygnus is in storage inside a clean room at Wallops awaiting transportation to the Antares rocket's integration building when Orbital clears the launcher for flight. Ground crews will attach the spacecraft to the Antares rocket's second stage, then install an aerodynamic nose cone over the payload.

Then ground crews will load last-minute experiments and fresh food into the supply craft's pressurized module before rolling out to the launch pad two or three days prior to liftoff.

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