An expert panel convened by NASA has failed to find the root cause of the fairing-separation problem that destroyed the Glory atmospheric-research mission in 2011, raising questions about the Orbital Sciences Corp. Antares rocket scheduled to begin flying cargo to the International Space Station later this year.

Orbital built the Taurus XL rocket that launched Glory on March 4, 2011, only to see a second consecutive fairing-separation failure pull the $388 million mission back into the atmosphere instead of sending it to orbit. Another Taurus fairing-separation failure cost the U.S. space agency its Orbiting Carbon Observatory (OCO) mission in February 2009.

“Detailed analysis determined one of the side rails of the payload fairing system failed to fully fracture near the fairing’s nose cap,” the Glory Mishap Investigation Board reported Feb. 20. “However, no root cause for the fairing’s failure to separate was able to be determined.”

Telemetry data from both the Glory and the OCO failures led the Glory failure panel to conclude “that the post-fairing separation failure configurations of both vehicles were similar,” according to the latest report.

The panel did not release its full findings on the grounds that Orbital considers some of the information to be proprietary, and some of it restricted from foreign release under the International Traffic in Arms Regulations (ITAR). However, the panel suggested two “possible” intermediate causes of the Glory failure. One possibility is that the rubber charge holder in the pyrotechnic frangible joint that failed to separate fully may have “slumped due to the effects of launch acceleration and random vibration, resulting in incomplete fracture of the fairing side rails.”

Also on the “possible” list of intermediate causes was inadequate testing of not just the charge holder, but the rest of the frangible joint system “throughout the life cycle of the frangible joint.”

The Glory board’s summary states: “There may be additional undiscovered failure modes due to untested environments within the joint system. Analysis and testing must be applied to the frangible joint system and not solely to the charge holder.”

Limited flight telemetry and the lack of recovered hardware prevented discovery of the root cause of the Glory failure, according to the report summary. Panel members noted that “a large percentage of potential causes rated as ‘possible, but highly unlikely’ involved frangible joint components, and also observed that Orbital’s manufacturing processes were not as tightly controlled as those applied by NASA in other pyrotechnic hardware designs.

“The possibility exists that manufacturing process controls could allow variation in material properties and hardware dimensions that may impact system performance,” the report summary says.

An on-pad hot-fire test of Orbital’s Antares space station cargo rocket was aborted by the vehicle’s flight computer on Feb. 13, and the date for a first flight of the rocket from the Wallops Flight Facility on the Virginia coast has not been set. The company traced the automatic abort to low pressure levels during a nitrogen purge of the kerosene-fueled rocket’s aft compartment.

NASA had no immediate comment on the effect of the Glory failure review on the Antares mission. As of late last year the agency had not cleared the shroud-separation mechanism on Antares for flight to the ISS with Orbital’s Cygnus cargo vehicle. Both Antares and Cygnus were developed under NASA’s Commercial Orbital Transportation System seed-money program.