NASA Investigation into SpaceX’s Falcon 9 Explosion Questions Single Strut Theory
Dragon capsule separated from Falcon 9 launch vehicle.
While SpaceX blames a faulty strut supplied by a contractor for the explosion of a Falcon 9 rocket in June 2015, an independent investigation by NASA Launch Services Program (LSP) concluded there were several “credible causes” for the accident, including poor quality control at Elon Musk’s launch company.
“In addition to the material defects in the strut assembly SpaceX found during its testing, LSP pointed to manufacturing damage or improper installation of the assembly into the rocket as possible initiators of the failure,” according to a report published on Tuesday by the NASA Office of Inspector General (OIG). “LSP also highlighted improper material selection and such practices as individuals standing on flight hardware during the assembly process, as possible contributing factors.”
The information is contained in a new OIG audit, “NASA’s Response to SpaceX’s June 2015 Launch Failure: Impacts on Commercial Resupply of the International Space Station.” The report says LSP failed to find a probable cause for a failure that sent a Dragon supply ship carrying cargo for the International Space Station to the bottom of the Atlantic Ocean.
SpaceX’s investigation concluded the “most probable cause for the mishap was a strut assembly failure in the rocket’s second stage. Specifically, the failed strut assembly released a helium tank inside the liquid oxygen tank, causing a breach in the oxygen tank’s dome and the release of gas that in turn disabled the avionics and caused release of the Dragon 1 capsule and break-up of the launch vehicle….The company’s post-mishap testing of strut parts from the same purchase order as those used on SPX-7 found material flaws due to casting defects, ‘out of specification’ materials, and improper heat treatment.”
LSP’s findings alarmed officials at NASA, which awarded commercial cargo and crew contracts to SpaceX to service the International Space Station.
“In February 2016, the NASA Administrator and the Associate Administrator for the Human Exploration and Operations Mission Directorate sent a letter to SpaceX expressing concerns about the company’s systems engineering and management practices, hardware installation and repair methods, and telemetry systems based on LSP’s review of the failure,” the report reads.
The OIG reports that SpaceX has taken a number of corrective actions to address concerns about the strut and its processes.
“The company also reviewed the certifications of all spaceflight hardware and altered its quality control processes to better align with NASA technical standards,” the report reads. “In order to track completion of its corrective actions, SpaceX is updating its process for identifying and resolving work-related tasks, which allows for improved auditing, prioritizing, and tracking of fracturable hardware.
“To administer its updated quality control process, SpaceX has reorganized into three teams called ‘Design Reliability,’ ‘Build Reliability,’ and ‘Flight Reliability.’ Besides monitoring corrective actions taken as a result of the SPX-7 failure, these teams are tracking the significant upgrades SpaceX has made to the Falcon 9 launch system for future launches, including increased thrust capability with a new fuel mixture and corrective actions on software implementation plans, which are both rated as low risks by the ISS Program,” according to the report.
The relevant excerpt from the report follows.
NASA Office of the Inspector General
Excerpt from
NASA’s Response to SpaceX’s June 2015 Launch Failure: Impacts on Commercial Resupply of the International Space Station
SpaceX’s Return to Flight Plan
Following the SPX-7 failure, SpaceX recovered parts of the Falcon 9 rocket and, through telemetry analysis and other testing, determined the most probable cause for the mishap was a strut assembly failure in the rocket’s second stage. Specifically, the failed strut assembly released a helium tank inside the liquid oxygen tank, causing a breach in the oxygen tank’s dome and the release of gas that in turn disabled the avionics and caused release of the Dragon 1 capsule and break-up of the launch vehicle. SpaceX completed an extensive analysis of the SPX-7 failure, consulted with NASA and the United States Air Force (USAF) regarding their analysis, and provided a mishap report and Return to Flight Plan to the FAA and NASA in November 2015. The company’s post-mishap testing of strut parts from the same purchase order as those used on SPX-7 found material flaws due to casting defects, “out of specification” materials, and improper heat treatment.23
NASA’s Launch Services Program (LSP) conducted a separate, independent review of the failure, briefing its results to senior NASA leadership on December 18, 2015.24 LSP did not identify a single probable cause for the launch failure, instead listing several “credible causes.” In addition to the material defects in the strut assembly SpaceX found during its testing, LSP pointed to manufacturing damage or improper installation of the assembly into the rocket as possible initiators of the failure. LSP also highlighted improper material selection and such practices as individuals standing on flight hardware during the assembly process, as possible contributing factors.25
SpaceX has taken action to correct the deficiencies that led to the failed strut assembly and to address NASA’s concerns by conducting inspections, replacing suspect parts, and conducting additional testing. The company also reviewed the certifications of all spaceflight hardware and altered its quality control processes to better align with NASA technical standards. In order to track completion of its corrective actions, SpaceX is updating its process for identifying and resolving work-related tasks, which allows for improved auditing, prioritizing, and tracking of fracturable hardware.
To administer its updated quality control process, SpaceX has reorganized into three teams called “Design Reliability,” “Build Reliability,” and “Flight Reliability.” Besides monitoring corrective actions taken as a result of the SPX-7 failure, these teams are tracking the significant upgrades SpaceX has made to the Falcon 9 launch system for future launches, including increased thrust capability with a new fuel mixture and corrective actions on software implementation plans, which are both rated as low risks by the ISS Program.
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23 A casting defect is an irregularity that occurs when molten metal is poured into a mold and cooled. An “out of specification” material has a technical attribute (e.g., chemical composition, mechanical property) outside of the prescribed values for the type of metal specified for a particular use. Heat treatment at accurate temperatures strengthens metal parts while improper heat treatment can cause deviations or weaknesses.
24 LSP purchases commercial launch services for NASA customers, including missions of the Agency’s Science Mission Directorate. LSP had a contract with SpaceX to use the Falcon 9 to deliver a science mission payload.
25 In February 2016, the NASA Administrator and the Associate Administrator for the Human Exploration and Operations Mission Directorate sent a letter to SpaceX expressing concerns about the company’s systems engineering and management practices, hardware installation and repair methods, and telemetry systems based on LSP’s review of the failure.
