SpaceX will need another six weeks to complete the implementation of hundreds of modifications to its Super Heavy/Starship rocket and the gargantuan booster’s Texas launch pad before it is ready for a second attempt to reach orbit, company founder Elon Musk said on Saturday.
This assumes the Federal Aviation Administration clears clearance to fly following the Super Heavy’s spectacular April 20 launch, in which the rocket exploded after multiple engine failures and the Starship’s upper stage failed. failed to separate from the first stage thruster.
In a Twitter Spaces chat with author Ashlee Vance, Musk said SpaceX is implementing “well over a thousand ‘changes’,” and “I think the likelihood of this next flight working, getting into orbit, is much higher than the previous one. Maybe it’s like 60%. It depends on how well we manage to separate the stages.”
The reusable Super Heavy first stage has 33 methane-fueled Raptor engines, while the Starship second stage has six. The original design called for the Super Heavy’s engines to shut down after propelling the ship out of the lower atmosphere. The spacecraft would then separate and ignite its own engines to continue in orbit. SpaceX is building a variant of the Starship to serve as a lunar lander in NASA’s Artemis program.
During the Super Heavy’s maiden flight, half a dozen engines quit or never started, and the Starship never separated from the Super Heavy’s first stage.
After reaching an altitude of about 24 miles, the entire vehicle began to crumble, falling about six miles before its self-destruct system activated, detonating the rocket. The self-destruct system took longer to respond than expected.
For his second flight, Musk said the floor separation system had been changed, a “last-minute change that is really, really important.”
Starship engines will start firing before all Super Heavy engines have shut down. This so-called “hot staging” technique has been used for years in Russian rocketry and Musk said it will improve the performance of the Super Heavy-Starship.
“We shut down most of the booster engines, leaving just a few running, and then at the same time we started the ship engines, or the upper stage engines,” he said. “Obviously this leads to some sort of blasting of the booster, so you have to protect the top of the boost stage from being incinerated by the upper stage engines.”
The solution is to add shielding to the top of the Super Heavy stage, as well as an extension that has vents to direct the exhaust plumes from the upper stage engine away from the lower stage when they initially start.
“There is a significant payload-to-orbit advantage with hot staging, i.e. a conservative improvement of about 10% if you never stop pushing,” said Musk. “To do that you actually have to have vents, the super hot plasma from the upper stage engines has to go somewhere.
“So we’re adding an extension to the booster which is almost all vents, basically. So that allows the upper engine plume to go through the vented extension of the booster and not just blow itself out. So that’s the riskiest thing , I think, for the next flight.”
Addressing engine issues encountered during the rocket’s first flight, Musk said engineers are implementing modifications to the Raptor’s hot gas manifold that directs superheated methane-rich gas to the combustion chamber. High temperatures can create leaks through the bolt holes where the manifold is attached.
The manifold itself has been redesigned, Musk said, and higher torque settings will be used to tighten the bolts more securely and eliminate potential bolt hole leaks.
Another major issue being resolved: damage to the Super Heavy/Starship launch pad at SpaceX’s flight test facility in Boca Chica, Texas.
During the Super Heavy’s maiden flight, exhaust from the Raptor engines on the first stage severely eroded the concrete footings of the platform. Musk said the company is adding about 1,000 cubic meters of steel-reinforced high-strength concrete.
“On top of that, we have a kind of steel sandwich, which is basically two thick steel plates that are welded together with channels going through (with) perforations in the top, so it projects in makes a lot of water,” he said.
“Think of it like a gigantic upside-down showerhead. It will basically blow water upwards while the rocket is above the pad to counter the massive amount of heat from the booster. The booster is basically like the biggest cutting torch in the world with a massive amount of…heat, but also a massive amount of force.”
He said the changes were “over the top” and should leave “the base of the pad in much better shape than last time”. Additionally, the rocket will take off at a higher throttle setting to get the vehicle away from the pad faster.
One issue that didn’t come up in Saturday’s discussion was the Super Heavy/Starship’s self-destruct system, which took much longer than expected to activate after the rocket spun out of control in April.
The FAA will need to approve this system and any other safety-related upgrades before a launch license will be granted.
Asked how much SpaceX has invested in the Super Heavy/Starship program to date, Musk said he doesn’t know the exact amount, “but it’s over $2 billion” and could approach $3 billion. by the end of this year.
Asked what he sees as the biggest challenge facing the Super Heavy/Starship in terms of producing a commercially viable rocket, Musk said he doesn’t know yet “because we don’t have yet reached orbit.
“If we knew what it was, we would fix it before launch,” he said. “So in launching, what you’re doing is trying to figure out the unknowns that you can’t know before you launch, or at least we’re not smart enough to know. So, as I’ve said, what seems to be the biggest risk right now is stage separation.”