SpaceX is hopeful launches of its Falcon 9 rocket will resume by the end of the year as it narrows down the possible causes of the explosion on September 1 that destroyed the booster and its AMOS-6 satellite payload. The company says it suspects the cause of the incident was improper loading of one of the cryogenic helium bottles inside the second stage liquid oxygen (LOX) tank, which could be addressed in a short time frame.

According to SpaceX, the Accident Investigation Team, which includes investigators from SpaceX, the FAA, NASA, the US Air Force, and private industry, is continuing to pore through evidence from physical remains to launch pad telemetry as it seeks to identify the cause of the explosion.

One major part of the investigation has been SpaceX's attempts at its McGregor, Texas facility to recreate the accident. The company says the most probable cause of the accident was a malfunction in one of three Composite Overwrapped Pressure Vessels (COPVs) inside the second stage LOX tank. These tanks are made of titanium wrapped in layers of carbon composite fibers to withstand the pressure of the liquid helium used to pressurize the propellant tanks that power the second stage engine.

Though exactly what happened during the incident is still unclear, the starting point was most likely the failure of one of the helium bottles, which flooded the LOX tank that then ruptured from sudden overpressure, leading to the explosion. The question facing SpaceX is whether the failure of the COPV was due to a design flaw or from it being improperly filled during the fueling process.

This is very important for SpaceX because if it was a fueling error, then it can be resolved by changing procedures, introducing new safety checks, or adjusting the pressure and temperatures at which the helium is loaded. These would allow SpaceX to get the green light for launching in short order. Alternatively, if it turns out to be a fault in the bottle itself, that will mean redesign, retesting, and refitting before another mission could lift off.

SpaceX says it will resume stage testing in Texas in a few days and that its launch sites in Florida and California remain operational.