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NASA and Orbital don't agree on what caused last year's rocket explosion

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NASA and Orbital Sciences can't seem to agree on exactly what caused Orbital's Antares rocket to explode on the launch pad last October. The space agency released its accident report this week, and while it concludes some of the same things that Orbital found out about the accident, it contradicts Orbital’s own investigation in one key way.

On October 28th, 2014, Orbital's Antares rocket had been slated to bring food, water, and supplies for the crew of the International Space Station. The launch was part of NASA's Commercial Resupply Program, which tasks commercial companies with periodically resupplying the station. But just 15 seconds after liftoff from NASA's Wallops Flight Facility in Virginia, the rocket blew up in a fiery nighttime display.

After looking into the failure, NASA believes that an explosion occurred in the turbopumps, or the spaghetti-like tubes, on one of the two main AJ-26 engines used on the Antares, according to a new report released by a NASA Independent Review Team (IRT). Somehow, pieces of the turbopumps rubbed together and ignited, causing the engines to lose thrust and the rocket to fall back to Earth, NASA said. However, the report fails to pin down what caused the turbopump's to rub together.

NASA's findings both confirm and contradict Orbital's own investigation

The NASA findings both confirm and contradict Orbital's own accident investigation into the incident, which was released to the FAA earlier this year. Orbital also agrees that pieces of the turbopumps came together, causing enough friction to set on fire, according to SpaceNews. But Orbital says the most likely cause was a defect in how the turbopumps were made. That places much of the blame on Aerojet Rocketdyne, the company that makes the AJ-26 engines. These engines are based off the NK-33 engine, which was designed by the Soviet Union in the 1960s and 70s.

NASA says it's definitely possible there was a defect in the way the AJ-26 engine was manufactured. However, NASA also argues there are two other equally likely causes for the failure. One could be that the design of the AJ-26 engine wasn't "robust" enough, and the way the turbopumps were built made them susceptible to fires. Another option is that foreign debris caused the accident. Weird titanium and silica objects were found in the engine at the crash site, but there was no way to confirm if these objects caused the explosion.

Orbital largely dismissed the idea that foreign debris was to blame, according to SpaceNews, but Aerojet Rocketdyne argued earlier this year that these objects caused the explosion. If foreign debris were found to be the cause, then Aerojet wouldn't be at fault for the failure, and the explosion could be considered Orbital's fault for not assembling the rocket correctly. Despite a lack of consensus, Aerojet did agree to pay $50 million to Orbital in order to settle the dispute over the accident.

Meanwhile, Orbital is gearing up for its first launch attempt since the failure; the company will launch its Cygnus cargo craft, filled with supplies for the International Space Station, aboard an Atlas V rocket on December 3rd. Eventually, Orbital will launch the Cygnus on its Antares rocket again in May of next year, though the rocket will use Russian-made RD-181 engines rather than the AJ-26 engines.