A SpaceX Falcon 9 rocket exploded on Cape Canaveral Air Force Base launch pad in Florida last Sept. 1. Until today, authorities and SpaceX are still investigating what could have caused the explosion. But despite that SpaceX already expressed its intent to proceed with its refueling processes that worry NASA today.

SpaceX is a private spaceflight company owned by billionaire Elon Musk. It is known for its unorthodox ways and is the number one proponent of reusing rockets to make the cost of space explorations cheaper.  NASA thinks SpaceX' fuelling system is 'unreasonably dangerous' and 'too risky' according to a report.

Although the company had its fair share of success under its belt, it is also facing one of the most difficult 'anomalies', the explosion of its Falcon 9 rocket last Sept. 1 while being fuelled. The cause remains a mystery since there is no activated engine at the time of the explosion that means there is no apparent heat source to cause the blast.

NASA is reportedly questioning SpaceX and its fuelling system. This process is being dissected by experts and is under investigation after the explosion. Even before the explosions, members of the International Space Station  (ISS) advisory committee already questioned the safety of SpaceX fueling system if astronauts are on board. The concern was expressed last December, according to a report by the Wall Street Journal.NASA gave non-binding recommendations for spaceflight safety and the welfare of the crew.

There are a couple of theories as to what could have caused the explosion including 'sabotage' angle since SpaceX requested to inspect its competitor's rooftop where an alleged weird light was spotted right before the explosion. However, Musk and the investigators are firm in saying that there's not truth to that.

Musk's space flight company services employ a different process when loading fuel in its rocket compared to its competitors. And NASA had already expressed its concern about this process before and after the explosion, a report said. SpaceX uses 'superchilled' liquid oxygen to pack more fuel inside the tank. This way, the power during liftoff can hoist heavy payload is increased. The fueling process has to be done right before liftoff to maximize the efficacy of the procedure.

The explosion could be attributed to a glitch in the pressurization vessel in the second stage of the rocket, but despite that investigations are still ongoing.

SpaceX already said that it would be enhancing its helium loading system to make the process reliable. All Falcon 9 rockets are also grounded since the blast in September. Meanwhile, SpaceX issued a statement in response to NASA's concern.

"Over the last year and a half, NASA and SpaceX have performed a detailed analysis of all potential hazards," a SpaceX official said in a statement. "These analyses and controls will be carefully evaluated in light of all data and corrective actions resulting from" further investigations concerning the explosion that occurred last September.