In a private chat for subscribers only held on April 29th, Elon Musk predicted that the company would be ready to make another launch attempt in about two months with a greater chance of reaching space.
“The outcome was roughly sort of what I expected and maybe slightly exceeded my expectations,” he said. Those expectations, he said, were that the vehicle would get clear of the pad and get “significant” data during the flight, including through maximum dynamic pressure or max-Q. “Overall, I actually feel like that was a great flight.”
Musk gives a good, detailed account of the flight and it's captured at that link to SpaceNews.com. He says that at launch three engines out of 33 either failed to start or were shut down by the controlling systems. Musk added, “Those engines did not explode, but the system didn’t think they were healthy enough to bring them to full thrust.”
Still, the 30 engines running at that point are the minimum number required
for liftoff. This was the cause of the Starship stack leaning away from
the Tower as it cleared the pad that many people had noted.
At T+27 seconds, a Raptor designated engine 19 lost communications at the same time that “some kind of energetic event” broke off part of the heat shield around that engine and three others. At that point there were “visible fires” coming from the aft end of the rocket, he said.
At T+62 seconds, there was additional heat shield damage around another Raptor, engine 30, although that engine continued to operate. At T+85 seconds, “things really hit the fan,” he said, with the loss of communication with another engine. “Roughly from this point onwards, we lose thrust vector control of the rocket,” he said, meaning it could no longer steer.
Interestingly, Musk said that they don't conclusively know what caused the engines to fail, but feels that they have no specific evidence that the failures were caused by the “rock tornado” of debris from the concrete pad created by the thrust of the engines at liftoff.
“Weirdly, we do not see evidence of the rock tornado actually damaging engines or heat shields in a material way,” he said. “It may have, but we have not yet seen evidence of that.”
One would think that sort of evidence would be most easily observed on the
wreckage, but there's no specific mention of them having recovered the
wreckage for failure analysis (autopsy). The area where the wreckage fell into the Gulf
should be known accurately enough to make search and recovery fairly
straightforward. Or as straightforward as recovering tens of thousands of pounds of steel and wreckage ever gets.
Another oddity was that they had difficulty terminating the flight. This seems like it could have been related to the hydraulic systems being damaged early in the flight.
SpaceX made no attempt to separate the Starship upper stage from the Super Heavy vehicle as it tumbled in later stages of flight. Musk said while controllers initiated the flight termination system, it took much longer than expected, about 40 seconds, for explosives to rupture the vehicle’s tanks.
Requalifying that flight termination system will be the long-lead item for the next launch, he predicted, with the next vehicle and a repaired pad likely ready in six to eight weeks. “Hopefully, we’ll be ready to fly again in a couple months.”
Musk played down damage to the pad, including the concrete debris scattered for 400 acres around the pad and the concrete dust that fell over 6 miles away. “The debris was basically sand and rocks,” he said, “but we don’t want to do that again.”
Changes to the pad include placing a water-jacketed “steel sandwich” below the launch mount. “You have what’s basically a massive super strong steel showerhead pointing up,” he said, with that water deluge system mitigating dust and debris.
He said SpaceX will also be replacing damaged tanks in the tank farm at the pad that were already set to be swapped out with vacuum-jacketed versions. The launch tower itself suffered no “meaningful” damage, he added.
The next launch will use a Super Heavy booster called Booster 9, but he said the company had not decided which of the Starship upper stages will fly. “The engines on Booster 9, which is next, are much newer and more consistent, and with significant reliability improvements,” he said, along with improved shielding. “I think we’ll see a much more robust engine situation with Booster 9.”
Unlike before this launch, Musk said he thought there was a “better than 50% chance of reaching orbit” on the next launch. More surprisingly (to me), he said he expected SpaceX to attempt four to five Starship launches this year.
“I would be surprised if we exit this year without getting to orbit,” he said, giving the company an “80%-plus probability” of doing so, increasing to nearly 100% within 12 months.
He said the company will spend about $2 billion this year on Starship, which he argued the company can support without raising outside funding.
“Once again, excitement is guaranteed,” Musk said of the next launch. “Success is not.”
Starship test flight, April 20th. SpaceX photo