SpaceX will need about six more weeks to implement hundreds of changes to its Super Heavy/Starship rocket and the giant launch vehicle’s Texas launch pad before it will be ready for a second attempt at orbit, company founder Elon Musk said on Saturday.
This assumes that the Federal Aviation Administration will clear the Super Heavy to fly after its dramatic April 20 maiden launch, in which the rocket self-detonated after multiple engine failures and the spacecraft’s upper stage failed to separate from the first-stage booster.
In a Spaces discussion on Twitter with author Ashlee Vance, Musk said that SpaceX is making “well over a thousand” changes and “I think the likelihood of this next flight working and getting into orbit is a lot higher than the last one.” .” Maybe it’s 60%. It depends on how well we do at phase separation.”
A SpaceX Super Heavy Booster (silver) and a spacecraft upper stage (black) are seen at their launch stand at the company’s flight test facility in Boca Chica, Texas. The fully reusable two-stage rocket is the most powerful in the world. SpaceX
The Super Heavy’s reusable first stage features 33 methane-powered Raptor engines, while the Starship second stage has six. The original design called for the Super Heavy’s engines to shut down after the spacecraft was elevated from the lower atmosphere. The spacecraft would then separate and fire its own thrusters to continue into orbit. SpaceX is building a variant of the Starship to serve as a lunar lander in NASA’s Artemis program.
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During the Super Heavy’s maiden flight, half a dozen engines died or never started, and the spacecraft never separated from the Super Heavy’s first stage.
After reaching an altitude of only about 24 miles, the entire craft began to tumble and crashed about six miles before its self-destruct system activated and the missile blew to pieces. The self-destruct system took longer than expected to respond.
For his second flight, Musk said the stage separation system was modified, a “late game-breaking change that’s really very significant.”
The spaceship’s engines begin firing before all of the super-heavy engines shut down. This so-called “hot staging” technique has been used on Russian missiles for years, and Musk said it would improve the Super Heavy-Starship’s performance.
“We shut down most of the booster engines, let only a few run, and then started the ship’s engines or the upper stage at the same time,” he said. “Obviously that results in the booster being blown up, so you have to protect the top of the boost stage from being burned by the upper stage thrusters.”
The solution is to add a shield to the top of the Super Heavy stage and add an extension with vents to direct the upper stage engine’s exhaust plumes away from the lower stage on initial launch.
“With hot staging, there’s a significant payload-to-orbit advantage that conservatively equates to about a 10 percent improvement if you basically just never stop thrusting,” Musk said. “To do that you actually need vents, the super-hot plasma from the upper stage engines has to go somewhere.
“So we add an extension to the booster that’s basically just vents. This allows the upper engine plume to flow through the vented extension of the booster and not just blow itself up. That’s the riskiest thing in my opinion.” Think about the next flight.
To address engine problems encountered during the rocket’s first flight, Musk said engineers are making changes to the Raptor’s hot gas manifold, which directs superheated methane-rich gas into the combustion chamber. The high temperatures can create leak paths through the bolt holes that the manifold is attached to.
The manifold itself has been redesigned, Musk said, and higher torque settings are used to tighten the bolts more securely and eliminate potential leak paths in the bolt holes.
Another major issue being addressed: 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 first stage engines severely eroded the platform’s concrete foundations. Musk said the company is in the process of adding about 1,000 cubic yards of high-strength reinforced concrete.
“On top of that, we have a sort of steel sandwich, which is basically two thick steel plates welded together, with channels (with) perforations running down the top, so there’s actually a lot of water splashing out,” he said.
“Think of it like a gigantic shower head turned upside down. It will basically blow water up while the rocket is over the pad to counter the tremendous amount of heat from the booster. The Booster is basically like the largest cutting torch in the world with a massive amount of… heat, but also a massive amount of power.
He said the modifications were “overkill” and should result in “the base of the pad being in much better shape than last time.” In addition, the rocket launches with a higher throttle setting to get the vehicle off the ground faster.
One issue not raised in Saturday’s discussion was the Super Heavy/Starship’s self-destruct system, which took much longer than expected to activate after the missile went out of control in April.
The FAA must approve this system and any other safety-related upgrades before a launch license is granted.
When asked how much SpaceX has invested in the Super Heavy/Starship program so far, Musk said he doesn’t know the exact amount, “but it’s over $2 billion” and could be close to $3 billion by the end of this year -dollars.
When asked what he thinks is the biggest challenge for the Super Heavy/Starship in terms of making a commercially viable rocket, Musk said he doesn’t know yet “because we haven’t reached orbit yet.”
“If we knew what it was, we would actually fix it before launch,” he said. “So at launch you’re trying to resolve the unknowns that you may not know before launch, or at least we’re not smart enough to know. As I said, the biggest risk right now seems to be stage separation.”
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