SpaceX’s “fail fast, learn faster” mentality means that the company does not expect everything to go right during a test flight.
But sometimes a failure is more edifying than just brainstorming everything that could go wrong.
“In launching, what you’re doing is trying to resolve the unknowns, which you cannot know before you launch,” Elon Musk, the founder and chief executive of SpaceX, said in June during an audio discussion on Twitter, now renamed X.
“Or at least,” Mr. Musk said, “we are not smart enough to know.”
At first glance, the Starship rocket on the launchpad on Saturday looks like the same behemoth vehicle that launched in April. It is not.
“There are really a tremendous number of changes between the last Starship flight and this one,” Mr. Musk said. “Well over a thousand.”
The biggest change is something called “hot staging.”
For current American rockets, including SpaceX’s Falcon 9, just before the booster drops away, its engines shut down. The rocket coasts before the booster separates from the upper stage, and only then does the second-stage engine ignite.
With hot staging, Starship’s upper-stage engines will ignite while the booster is still attached and some of the booster engines are still firing. Hot staging, which is commonly used on Russian rockets, could improve the performance of Starship by 10 percent, Mr. Musk said.
Hot staging also “results in kind of blasting the booster,” Mr. Musk said. As a result, a shield was added to the top of the booster to protect it, and a cylindrical segment with vents has been added between the stages. The vents allow the hot gases from the upper-stage engines to flow out into space.
Many of the other changes fix things that went wrong during the April flight. The Federal Aviation Administration set out 63 corrective actions that it said SpaceX had to undertake before a new launch license could be issued.
On the rocket, SpaceX made changes to the design to prevent fuel leaks and fires and improvements to safety systems, including the flight termination system that took much too long to destroy the Starship.
SpaceX added shields between the engines so that an explosion disabling one of them would be less likely to take out neighboring engines as well.
“If you lose one of 33 engines, that’s a 3 percent thrust loss,” Mr. Musk said in April during a Twitter audio discussion. “It’s not a big deal. But if you do not have good engine isolation and an engine failure can domino to other engines or to parts of the stage, then you have an extremely unreliable design.”
For the launchpad, to prevent the rocket engines from destroying the concrete below and sending up a cloud of debris and dust, SpaceX has added a structure that consists of two plates with holes on the top plate. “Basically, a massive, super strong steel shower head pointing up,” Mr. Musk said.
Hundreds of thousands of gallons of water sprayed upward from this system will act as a cushion absorbing the heat and force of the rocket engines, protecting the steel and concrete .
Despite all the changes, something else could go wrong. Mr. Musk said the part of the second flight likeliest to cause problems would be the hot staging. But there is always room for surprises.
“We don’t know with accuracy what the most important thing is, because we’ve not yet reached orbit,” Mr. Musk said. “If we knew what it was, we would actually fix it before launching.”
