SpaceX explosion remains a mystery

The spectacular explosion of a SpaceX rocket has turned into a full-blown mystery after Elon Musk took to Twitter to say the company is so baffled about what happened that it needs help from the public.

There was a mysterious bang of unknown origin seconds before ignition, he noted. There was no apparent source of heat that could have ignited the blast, he added. And then he refused to rule out the rampant Internet speculation that something - a drone? - may have crashed into the rocket, fueling rumors of sabotage.

He did, however, seem to discount alien involvement.

Since it was founded in 2002, SpaceX has experienced its share of failures. Its first three test rockets blew up, nearly bankrupting the company. Last year another, more powerful rocket exploded a few minutes into its flight to deliver more than $100 million in cargo to the International Space Station.

But the loss of its Falcon 9 rocket last week is "turning out to be the most difficult and complex failure we have ever had in 14 years," Musk said on Twitter early Friday.

The cause of the fireball was especially puzzling because it occurred during a "routine filling operation," Musk tweeted.

He noted that the rocket's "engines were not on and there was no apparent heat source."

One clue he said investigators were exploring was a "bang sound" that may have come from the "rocket or something else" seconds before the rocket blew up while standing on its launchpad at Cape Canaveral Air Force Station.

The confusion over the cause stands in contrast to its previous failure, in June 2015. That time, Musk pinpointed the problem shortly after the explosion, suggesting there was an "overpressure event" in a liquid oxygen tank in the upper stage of the rocket.

After determining that a small strut had broken, the company returned to flight after six months.

SpaceX is leading the investigation with help from the Federal Aviation Administration, NASA and the Air Force.

More than half of the members of the investigation team are from outside the company, according to an industry official with knowledge of matter who spoke on the condition of anonymity because he is not authorized to speak publicly about an ongoing investigation. They will have access to raw data and the ability to analyze it independently.

Still working on the Falcon fireball investigation. Turning out to be the most difficult and complex failure we have ever had in 14 years.

— Elon Musk (@elonmusk) September 9, 2016

The setup of the investigation is similar to that of the probe into SpaceX's explosion last year, when a rocket hired under a NASA contract headed for the International Space Station but blew up a few minutes into flight.

At the time, members of Congress said they had "serious reservations" about SpaceX leading the probe, and they expressed concern over whether the "investigation and engineering rigor" being applied would be sufficient to prevent further mishaps.

Particularly trying to understand the quieter bang sound a few seconds before the fireball goes off. May come from rocket or something else.

— Elon Musk (@elonmusk) September 9, 2016

But under FAA regulations, launch providers handle investigations when there is no loss of life, injury or outside property damage. The aerospace company now known as Orbital ATK, which lost a rocket in 2014, also led its own investigation.

It is unclear how long the new investigation will take or how long it will require to repair the launchpad.

Analysts have said that since the explosion occurred on the ground, there should be more evidence to recover than following explosions that occur in flight, when wreckage tends to be lost at sea. Still, SpaceX pleaded with the public to turn over any "audio, photos or videos" of the incident that could help the investigation.

When asked on Twitter about speculation that some object may have hit the rocket, Musk responded, "We have not ruled that out."