WASHINGTON — Orbital Sciences Corp. plans to redesign the fairing separation mechanisms for its rocket fleet as part of its plan to recover from back-to-back Taurus XL launch failures that destroyed two NASA Earth observing satellites, a senior company official said.

Both mishaps were attributed to a failure of the small launcher’s protective nosecone to open up and release its payload. Orbital uses similar fairing separation mechanisms on its other rockets including the medium-lift Antares, developed with NASA funding to deliver supplies to the international space station.

In a Feb. 21 interview, Ronald Grabe, executive vice president of Orbital’s Launch Systems Group, said redesigning the fairing separation mechanism is part of a “belt and suspenders approach” to fixing the problem, whose origin remains a mystery.

Just one day earlier, NASA issued a report saying it could not identify the root cause of the 2011 Taurus XL failure that destroyed its $424 million Glory climate-change research satellite.

“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 said in a summary of its final report. “However, no root cause for the fairing’s failure to separate was able to be determined.”

The board, formed in March 2011 just days after Glory was lost, was chaired by Bradley Flick, director of the Research and Engineering Directorate at NASA’s Dryden Flight Research Center in Edwards, Calif.

“We’re quite certain that we can narrow the field down to the fact that we had a problem with the frangible joint,” Grabe said. A frangible component is one that is designed to shatter under stress.

In Orbital’s fairing separation system, which Grabe said is used on “just about all of our vehicles,” a small explosive charge is used to fracture frangible components. This allows a rocket to shed its fairing when it is no longer needed to protect the payload.

It remains unclear whether mechanical or material factors prevented the fairing from opening.

It is possible, Grabe said, that something went wrong in the detonation-driven chain reaction intended to fracture the fairing’s aluminum joint. It is also possible that the joint itself was too soft to fracture at all, he said.

Grabe said the same suppliers provide fairing components for all Orbital rockets, including Antares, which is slated to debut carrying a dummy payload this year.

In addition to redesigning the fairing separation mechanism, Orbital plans to conduct its own inspection of parts previously certified solely by suppliers.

“It’s ‘trust, but verify,’” said Grabe, a former astronaut who served as a liaison to the commission that investigated the 1986 Space Shuttle Challenger accident.

Grabe would not say whether Dulles, Va.-based Orbital had altered or terminated relationships with any suppliers as a result of the back-to-back Taurus XL failures. The first of those destroyed NASA’s Orbiting Carbon Observatory (OCO) environmental monitoring satellite.

Many of the details of the Glory mishap investigation board’s report were left out of the eight-page summary released Feb. 20 by NASA. The agency said it had to protect proprietary Orbital information, and also that some of the information in the full report was subject to U.S. International Traffic in Arms Regulations.

“This was hard for us because we lost OCO first and then we lost Glory in very similar failures,” William Gerstenmaier, associate administrator for NASA’s Human Exploration and Operations Mission Directorate, told the NASA Advisory Council back in November. “It’s not good to have two failures in a row. That meant to us we didn’t do a good job on OCO.”

Gerstenmaier said then that it was unlikely that NASA or Orbital would ever be able to say for certain why Taurus XL’s fairing did not open for either the OCO or Glory launch.

The solid-fueled Taurus XL is still available under the NASA Launch Services-2 contract — the indefinite-delivery, indefinite-quantity rocket catalog from which NASA selects its expendable rockets. But to win actual launch contracts, the company must submit an acceptable return-to-flight plan to NASA, which could involve flying another agency satellite.

“It is up to Orbital to propose a return to flight plan for the Taurus XL, and it is up to NASA to determine if it is sufficient,” Jim Norman, director of the NASA Launch Services Program, said in a Feb. 22 email.

“Orbital’s ongoing investigation and test program, which is in its final stages, forms the foundation for a return-to-flight program,” company spokesman Barron Beneski said Feb. 22.

Grabe said Orbital is eying potential return-to-flight opportunities, but declined to be specific. “We have a couple of customers that we’re pursuing that hopefully will result in the ability to conduct a return-to-flight type of mission that actually has a paying customer for it,” he said.

Michael Freilich, director of NASA’s Earth Science Division, said the agency has lost about $1 billion between the Glory and OCO launch failures.

Last year, as part of a three-flight bulk buy, NASA awarded United Launch Alliance of Denver a $412 million contract to launch two Earth science missions and a civilian weather satellite aboard Delta 2 rockets. The payloads included OCO-2, a copy of the satellite lost aboard Taurus XL in 2009. OCO-2 was supposed to be Taurus XL’s return-to-flight payload, but NASA revoked the company’s launch contract after Glory was lost.

Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...