News Changes to the SpaceX BFR rocket.

GLS

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Lots of missing tiles...
media%2FF_OUsV6bgAEyA86.jpg
 

diogom

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Watch the launch video on post 315, it is very visible there.
Yep, it's engine chill most likely, not a concern.

Seems most of the problematic tiles are the glued-on ones along weld lines. They were going through S28 with a suction thingymajig a while back, so hopefully they're already on it. Didn't have high expectations for 25's after a tile fell off in the wind last week.

And there we go:
1700327967885.png
Wonder what flew off then.
 

Urwumpe

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At least the metal got pretty well heated, if you regard the discoloring.
 

diogom

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From the final Fish and Wildlife report, they claim up to 190 pounds of steel could be ablated in a launch, so it definitely got toasty. It's more apparent from this angle:
1700332775550.png
The spots under each engine have much higher water flow, the scorching really makes that pop.
 

Thunder Chicken

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Scott Manley's take:


Interesting diagnosis - he suggests that the thrust of the Starship during hot staging decelerated SuperHeavy, overwhelming the thrust of the remaining 3 Raptors and causing them to lose ullage. This caused loss of fuel pressure and caused the engine shutdowns, which he suggests may have caused some N-1 style sloshing and water hammer that smashed up pipes and caused the explosion.

He also points to some video and data that shows a large LOX leak in Starship coincident with a gas cloud being observed. He suggests that LOX depletion and early SECO triggered the AFTS as they didn't quite have enough velocity for orbit.
 

Thunder Chicken

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It seems like the dynamics of hot staging really weren't fully examined, and both stages were lost due to effects of that procedure. SH was decelerated by the thrust of Starship which set up a pogo oscillation in SH which starved the engines and either water-hammered it to death and/or lead to all engines shutting down and FTS triggering. Starship probably took a lot of damage in the aft skirt / engine bay during hot staging and ultimately lost LOX, causing early shutdown and FTS triggering of that stage.

Rapid iteration in design can be a great thing, but it seems like SpaceX excels at getting a good design built and polished, but then somebody swings in at the 11th hour and injects some major change that has to be hacked in and causes all sorts of unintended consequences because it couldn't be properly considered and integrated. Certainly there will always be unknowns that can only be understood by flight testing, but introducing "unknowns" that are only unknown because the organization creates them and can't stop to consider them is bad. That no one seemed to consider that the Starship thrusting on the top of SH applied a force in excess of the thrust of the three SH Raptors seems like the latter. This is an F=ma sort of calculation that really doesn't require a lot of exotic analysis, just someone with the ability to recognize the situation. That no one seemed to consider that firing all the Starship engines in a partially enclosed interstage could cause engine damage seems like an oversight. All of this is something that could have been examined with relatively simple and quick ground testing before integration into the stack. Putting a hot-staging interstage on a concrete pad, mocking up an Starship aft-skirt with some Raptors on top of it, and firing for a couple of seconds could have given them a lot of information about damage potential and the loads on SH without sacrificing a full stack.

On the scale of Blue Origin's "Gradatim Ferociter" philosophy where they never fly until everything is perfect (and nothing is ever perfect) to "F%*$ it, we're out of time. Send it and we'll patch it later", I wonder if SpaceX has their slider set a bit too far to the latter side of the scale. I worry when organizations are going faster than they can think.

I think they are going to struggle trying to get hot-staging to work and still maintain ullage in SH. Come to think of it, they may have ullage problems even without hot staging. Yes, other rockets have successfully used hot-staging, but those rockets were expending their first stages. SH will be relatively light compared to Starship (especially when it is flying payloads to full orbit) which means Starship will always have to have more much more thrust than the three Raptors on SH in order to effect separation. There will always be a net decelerating force on SH unless they decide to take the Starship engines and put them outside of the diameter of SH so the thrust does not impinge on it. If they put a long conical deflector on the top of the SH that might help, but that will increase the length and mass of the interstage, which rather defeats the performance benefits of hot staging. I think they may have to go back to the idea of serial staging unless they can find another means to maintain ullage, and even then it may still be a problem.
 
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Thunder Chicken

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Maybe somebody send this to SpaceX
5-076.jpg
Small external ullage motors on Starship would work for serial staging, but the idea of hot staging is that they minimize stage gravity losses by going full thrust at separation.

One thought would be to put some sort of deflector mechanism in the Starship aft skirt that would deflect the thrust at an angle out of the hot stage ring, but which could be retracted/jettisoned after SuperHeavy separated and turned away. That would impact performance somewhat, and would require more complicated hardware and moving bits to achieve which might negate any advantages.

Another hallucination thought would be some sort of temporary tether between StarShip and SH. As StarShip fired its engines, it would unreel this tether to provide just enough force to keep SH at a slightly positive acceleration. The problem with this is that it would act as a speed brake for Starship, again defeating the performance benefit of hot staging. And it couldn't begin to pitch around until the tether was separated.

I think that if they really want to hot stage, they are going to have to make StarShip look like the rocket in the TinTin comic with engines in the outriggers exhausting to the sides of SH:

The_Adventures_of_Tintin_-_16_-_Destination_Moon.jpg

I would be OK with the aesthetics of this design.
 
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Urwumpe

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They could just delay the reignition and the first maneuvers of the booster until the Starship is further away....
 

Thunder Chicken

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They could just delay the reignition and the first maneuvers of the booster until the Starship is further away....
Possibly, but they still need to ensure that the fuel is in the bottom of the tanks before reigniting the main engines. Perhaps they could do the pitch around maneuver with cold gas thrusters, then gimbal those thrusters to provide a linear ullage thrust. They don't need a lot of thrust - they just need to settle the fuel into the bottom of the tanks. They just have to accelerate the dry mass of the stage to slightly faster than the ballistic blobs of propellant.

If they could stay in the exhaust of Starship during the pitch around and do it relatively quickly, it might be possible that the exhaust of StarShip could assist maintaining ullage in SH. That may not be enough to do the job, but at least it wouldn't actively be wrecking the ullage state.
 

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Possibly, but they still need to ensure that the fuel is in the bottom of the tanks before reigniting the main engines.

That is what the header tanks in both Booster and Starship are for.
 

Thunder Chicken

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That is what the header tanks in both Booster and Starship are for.
I was not aware that the booster also had header tanks. If that is the case, then yes, it should just be a matter of waiting until Starship is clear and the hydrostatic pressure in the header tank and feedlines to stabilize.

If they were attempting to operate or relight engines while the booster was being decelerated by the thrust of Starship, the hydrostatic pressure gradient due to that deceleration would have been high in the header tanks and decreasing toward the engines engines, likely causing the turbopumps to cavitate. This is likely why one of the three engines that were burning through the separation cut out and why so many failed to light. If this is the case, they actually want to shut down all of the booster engines at separation, then relight them as necessary once the pitch around is complete and the pressure gradient is zero or positive toward the engines.
 

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Some incredible shots in these pages. Kind of hard to believe they're real and not concept art from the 60ies...
There's still a long way to go for starship, but it sure is a pretty sight!
 

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Some incredible shots in these pages. Kind of hard to believe they're real and not concept art from the 60ies...
There's still a long way to go for starship, but it sure is a pretty sight!

I can't wait to see and hear the booster landings😁
 
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