SpaceX founder and chief designer Elon Musk said Tuesday the June 28 failure of a Falcon 9 rocket that destroyed a space station-bound Dragon cargo capsule was a "huge blow" to the company and that conflicting data has made it difficult to determine the root cause of the mishap.
Speaking at the annual International Space Station R&D Conference in Boston, Musk said he hopes to be able to say "something more definitive toward the end of the week."
"At this point, the only thing that's really clear is there was some kind of over-pressure event in the upper stage liquid oxygen tank," he said. "But the exact cause and the sequence of events, there's still no clear theory that fits with all the data."
SpaceX holds a $1.6 billion contract with NASA to build and launch 12 space station resupply missions using the company's Falcon 9 rocket and Dragon cargo capsule. During launch of the seventh operational resupply mission June 28, the second stage liquid oxygen tank apparently ruptured around two minutes and 39 seconds into flight.
The rocket's nine first-stage engines were nearing the end of their planned burn and the booster continued flying as the second stage was engulfed in vapor. Seconds later, the vehicle disintegrated in a burst of fragments. The Dragon capsule apparently survived the rocket's initial breakup, transmitting telemetry as it plunged toward impact in the Atlantic Ocean.
Lost in the failure were more than 4,000 pounds of research gear, spare parts and supplies needed aboard the space station, including a spacesuit and a docking mechanism, the first of two intended for use by visiting U.S. crew ferry ships.
"Obviously, it's a huge blow to SpaceX," Musk said of the failure. "We take these missions incredibly seriously. Everyone that can engage in the investigation at SpaceX is very, very focused on that.
"In this case, the data seems to be quite difficult to interpret. Whatever happened is clearly not a simple, straight-forward thing. So we want to spend as much time as possible just reviewing the data, obviously going over it with NASA and the FAA and a number of other customers, and just sort of seeing what feedback everyone has, based on their prior experience, to see if we can get to what the most likely root cause is."
Sharing the stage with Mike Suffredini, NASA's space station program manager, Musk thanked the space agency for its help in the ongoing failure analysis.
"As soon as we think we've got a clear line on what happened, and we've cross checked it with as many experts as we can -- and we certainly appreciate the feedback from NASA on this front -- we'll certainly try to put out that story," Musk said. "My only reticence about saying something quite yet, I don't want to say something that subsequently turns out to be a misunderstanding of the situation."
The SpaceX failure was the third in seven space station resupply missions and the company's first Falcon 9 mishap in 19 flights dating back to the rocket's debut in 2010. Not surprisingly, Suffredini said the failures have combined to have a "big impact" on station operations.
"As a program, we always assumed we'd lose one or two logistics vehicles and that we'd have to deal with that," he said. "Never in my wildest dreams did I imagine we'd lose three in eight months. But you deal with the cards that are dealt, and so that's where we are today."
The first resupply incident occurred on Oct. 28, 2014, when an Orbital Sciences Antares rocket carrying a Cygnus cargo ship exploded seconds after liftoff. It was Orbital's third resupply mission under a $1.9 billion contract with NASA.
The Antares remains grounded as the company switches to different engines, but Orbital plans to launch a Cygnus supply ship atop a United Launch Alliance Atlas 5 rocket in December to help NASA make up lost ground.
In the wake of the Orbital failure, SpaceX's Dragon and Russia's Progress cargo craft took turns with four successful resupply missions in a row. But on April 28, a Russian Progress, the 59th launched to the station, spun out of control moments after reaching orbit and plunged back into the atmosphere a week and a half later.
Two months after that, SpaceX lost its seventh operational Dragon mission. In the back-to-back failures, NASA lost more than five tons of cargo and supplies.
The Russians resumed Progress flights on July 3, successfully launching the M-28M/60P mission from the Baikonur Cosmodrome in Kazakhstan. A Japanese HTV cargo craft is scheduled for launch in mid August and Orbital is on track to launch its next Cygnus capsule in early December. But it's too soon to say when SpaceX might resume flights.
"Our SpaceX colleagues have an in-depth knowledge of their vehicle, which they have largely built from the ground up," Suffredini said. "They have quite a bit of data on it, so I have high confidence in their ability to recover from this anomaly and get flying in time to continue to support the International Space Station."
Musk said company engineers are still trying to put together a precise millisecond-by-millisecond timeline based on telemetry from the rocket to pin down the root cause. At the same time, he added, the team will be on the lookout for any other problems that might have gone undetected to "maximize the probability of success for future missions."