The NESC investigation was initiated by NASA's Science Mission Directorate (SMD) in March 2010 after a mishap investigation board failed to find the root cause of the February 2009 OCO loss. The NESC team's findings are detailed in a 35-page report that references more than a dozen supporting documents chronicling the system's engineering development and test history dating to the early 1990s.
According to the document, when NASA first considered Taurus XL to launch the OCO and Glory missions in the 2005-07 timeframe, a certification plan was established by the agency's Launch Services Program (LSP) and a Taurus XL qualification process was set in motion to certify the vehicle for NASA missions. This process was aided by the fact that Taurus had already launched seven military and commercial payloads to low Earth orbit at the time.
As a result, much of the qualification process involved a review of engineering drawings and other paperwork associated with the rocket, including results of a 2002 test requested by the Missile Defense Agency (MDA) that qualified a frangible joint system similar to the one on Taurus XL and Pegasus.
NASA uncovered a number of issues with the 2002 MDA test as it related to Pegasus. This led to the first recommendations for requalification of the Pegasus frangible joint system being suggested in February 2006, when NASA's Safety and Mission Assurance office (SMA) recommended “pursuing the analysis of the failures and a subsequent requalification of this frangible ring assembly.”
In March 2006, the launch service program's chief engineer said “the main goal is to reconvene to set requirements for requalification to fully retire this risk.” One year later, in April 2007, SMA stated: “Qualification should be reperformed to account for the missing low-temperature test. This test would also serve to fix the test setup errors that may have caused the incomplete fractures during the ambient and high-temperature tests.”
On Dec. 1, 2008, NASA SMA recommended Orbital requalify the frangible ring—part of the frangible joint system—to show “appropriate thermal margins and clear up any test setup errors that may have contributed to the qualification discrepancies that this risk was written for.” Less than two months before NASA flew the OCO mission in February 2009, the agency's technical authority echoed this position.
It is worth noting that the frangible joint system in question has flown successfully on Orbital Sciences rockets, including Pegasus, Taurus XL and Minotaur. Despite the fairing-separation system's apparent flight-worthiness, however, it has never been qualified by NASA for Pegasus or Taurus XL missions.
Ultimately NESC determined the likelihood of another Taurus XL launch mishap as a result of the unqualified frangible joint system to be as much as 50%, though the report says mitigation efforts could have reduced or prevented the risk.
“Probability of occurrence is moderate,” NESC states, characterizing the frangible joint system's status as “flightworthy versus qualified (meaning less of a known quantity).”