SpaceX Moves One Step Closer to IFT2

Granted, I don't know how many steps there are before the second Integrated Flight Test, after the April 20th 1st test, but five days after last Wednesday's cryo testing, yesterday was an important milestone: a six engine, six second static firing of Ship 25.  Endless video loop here.  What appears to be moments before the start is here. (Six seconds is a SWAG - SiG)

Today, Ars Technica gave a bit of rundown on a few of the “well over a thousand” changes Elon Musk claims have been made to the Starship and Super Heavy itself as well as the Orbital Launch Mount or OLM.  We talked about one of the biggest changes, staging differently last week as well.  

SpaceX is adding an extension to the top of the Super Heavy booster with vents to allow super-hot gas from the upper stage engines to safely flow out of the rocket’s structure “and not just blow itself up,” Musk said. “This is the most risky thing, I think, for the next flight.”

Probably the next big change in this area is changing from the mechanical thrust vector control (TVC) of the older Raptors on the IFT1 to all of the Raptors on Booster 9 having the electrically driven TVC.  They've also added stronger shielding around each of B9’s 33 Raptor engines to protect them from explosions of nearby engines, a measure intended to reduce the chance of cascading failures. 

For the Starship’s second test flight, SpaceX teams are modifying manifolds on the Raptor engines that direct hot methane-rich gas toward each engine’s combustion chamber for mixing with oxygen-rich gas. The previous design was susceptible to leaks, where the hot gas could seep through bolt holes used to attach the manifold to the engine. Engineers will introduce an improved manifold design and add more torque to bolts to address the concern about leakage of super-heated gas.

Then there's the ground infrastructure, what Musk calls Stage Zero.  If you've watched any of the update videos, you've seen them adding many rebar cages for poured concreted deep under the OLM.  In addition, they've poured nearly 1,000 cubic meters of concrete underneath the launch pad’s pedestal, and over the steel-reinforcing cages.  

SpaceX will install two thick steel plates on top of the new layer of reinforced concrete, with channels routed through them to allow water to flow through and shoot out the top.

“Think of it like a gigantic upside-down shower head,” Musk said. “It’s basically going to blast water upwards while the rocket is over the pad to counteract the massive amount of heat from the booster.”

These few changes clearly aren't even 10% of the changes to the system if it's really over a thousand of them.  The big ones concern really understanding the rocket; “resolve the unknowns” that remain, many of which can’t be fixed until engineers gather data from an actual launch.  Reality brings that nagging reminder that they need to go through the process of getting FAA approval of their Flight Termination System again, since it took longer than expected to destroy the vehicle during the first IFT. The "longer than expected" time to work wasn't an issue since the vehicle was 24 miles above the Gulf of Mexico  and nowhere near a populated area.  That might not matter to the FAA at all. 

Musk acknowledged Saturday that it may not be up to SpaceX when the next Starship test launch happens. “There are a lot of variables here that are outside of our control.”